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In the modern poultry industry, with increasing product demand, muscle growth rate and meat yield in chickens have tremendously changed. Understanding the regulation of muscle development is important to maintain efficient growth and development in meat-type chickens. 20(S)-hydroxycholesterol (20S) is known as one of the naturally occurring osteogenic cholesterol derivatives due to its ability to induce osteogenic differentiation; however, no studies have evaluated myogenic response to 20S in chicken muscle cells. To determine the use of 20S in vitro for the proliferation and differentiation of chicken satellite cells, satellite cells were isolated from pectoralis major muscle of 4-week-old Ross 708 male chickens and subjected to 0.25, 0.5, and 1.0 μmol of 20S during their proliferation and differentiation stages. Cell proliferation and differentiation were measured every 24 h for 72 h by determining DNA concentration, the activity of creatine kinase, and the expressions of myogenic regulatory transcription factors. Together these results suggested that a lower concentration of 20S did not affect myogenesis but a high concentration of 1.0 μmol 20S can negatively affect proliferation and differentiation in chicken satellite cells.

Summary Skeletal muscle is composed of post-mitotic myofibers that form a syncytium containing hundreds of myonuclei. Using a progressive exercise training model in the mouse and single nucleus RNA-sequencing (snRNA-seq) for high-resolution characterization of myonuclear transcription, we show myonuclear functional specialization in muscle. After 4 weeks of exercise training, snRNA-seq reveals that resident muscle stem cells, or satellite cells, are activated with acute exercise but demonstrate limited lineage progression while contributing to muscle adaptation. In the absence of satellite cells, a portion of nuclei demonstrates divergent transcriptional dynamics associated with mixed-fate identities compared with satellite cell replete muscles. These data provide a compendium of information about how satellite cells influence myonuclear transcription in response to exercise., Graphical abstract, Highlights • Single nucleus RNA-sequencing, trajectory inference, and entropy analyses • Genetic depletion of satellite cells before exercise training in adult mice • Dysregulated nuclei arise 24 h after last exercise bout when without satellite cells • Satellite cell depletion alters myonuclear transcription during growth and adaptation, Biological sciences; Stem cells research; Transcriptomics

Summary Regeneration and repair of skeletal muscle is driven by tissue-specific progenitor cells called satellite cells, which occupy a minority of the cells in the muscle. This protocol provides researchers with techniques to efficiently isolate and purify functional satellite cells from human muscle tissue. The proven techniques described here enable the preparation of purified and minimally altered satellite cells for in vitro and in vivo experimentation and for potential clinical applications. For complete details on the use and execution of this protocol, please refer to Barruet et al. (2020) and Garcia et al. (2018)., Graphical Abstract, Highlights • Techniques are described for efficient isolation of human satellite cells • Quiescent and activated satellite cells are purified using surface markers • Purification involves minimal alteration compared to culture or activation • Purified satellite cells faithfully represent the natural state for applications, Regeneration and repair of skeletal muscle is driven by tissue-specific progenitor cells called satellite cells, which occupy a minority of the cells in the muscle. This protocol provides researchers with techniques to efficiently isolate and purify functional satellite cells from human muscle tissue. The proven techniques described here enable the preparation of purified and minimally altered satellite cells for in vitro and in vivo experimentation and for potential clinical applications.

Summary Regeneration of skeletal muscle requires resident stem cells called satellite cells. Here, we report that the chromatin remodeler CHD4, a member of the nucleosome remodeling and deacetylase (NuRD) repressive complex, is essential for the expansion and regenerative functions of satellite cells. We show that conditional deletion of the Chd4 gene in satellite cells results in failure to regenerate muscle after injury. This defect is principally associated with increased stem cell plasticity and lineage infidelity during the expansion of satellite cells, caused by de-repression of non-muscle-cell lineage genes in the absence of Chd4. Thus, CHD4 ensures that a transcriptional program that safeguards satellite cell identity during muscle regeneration is maintained. Given the therapeutic potential of muscle stem cells in diverse neuromuscular pathologies, CHD4 constitutes an attractive target for satellite cell-based therapies., Graphical abstract, Highlights • CHD4/NuRD regulates satellite cell (SC) fate commitment • CHD4 deficiency blocks SC proliferation and disrupts skeletal muscle regeneration • CHD4/NuRD repress myogenic differentiation genes during SC proliferative expansion • CHD4/NuRD represses genes associated with other fates (brain, heart) in SCs, In this article, Sreenivasan and colleagues show that the chromatin-remodeling complex CHD4/NuRD is required to maintain muscle stem cell (satellite cell) identity. CHD4 represses the skeletal muscle differentiation gene program during satellite cell proliferation and maintains genes from other lineages (brain, heart) silent, being essential for proper skeletal muscle regeneration.

Geminiviridae is one of the most important families in plant viruses with a single-stranded DNA genome comprises one or two genomes (DNA-A and DNA-B) of 2.5–5.2Kb. These viruses infect economically important food and fiber crops worldwide. Till to date nine genera (Mastrevirus, Curtovirus, Becurtovirus, Turncurtovirus, Begomovirus, Capulavirus, Topocuvirus, Eragrovirus, and Grablovirus) have been reported which are transmitted by four insect vectors (whiteflies, leafhoppers, aphids, and treehoppers). DNA-A encodes replication-associated protein, coat protein, replication enhancer protein, transcriptional activator protein, AV2, AC4, and AC5 while DNA-B encodes nuclear shuttle protein and movement protein. Satellite molecules have also been reported to be associated with the family Geminiviridae that includes alphasatellite, betasatellite which encode alpha rep and βC1 gene respectively. A non-coding deltasatellite has also been reported to be associated with geminivirus infections. Geminivirus encoded proteins interact with host proteins to perform a variety of functions which include reprogramming of cell cycle, inhibition of cell death pathways, transcriptional control of multiple genes, interference with cell signaling pathways and overcoming host defense response. Our current knowledge regarding interactions of geminivirus encoded proteins with the host has been described in the following chapter.

Skeletal muscle tissue-resident muscle stem cells, also called satellite cells, can undergo self-renewal and differentiation via adult myogenesis to generate muscle lineage through adult life. Satellite cells remain dormant in the quiescent state until the muscle suffers an injury. Upon damage to the muscle, the dormant satellite cells are activated, resulting in myogenesis mediated by its microenvironment. There is a progressive decline in the regenerative capacity of the muscles due to age-related impairment. Aging is negatively associated with satellite cell integrity because it loses its muscle cell microenvironment support during aging, which leads to cellular damage and results in impaired myogenesis and the accumulation of unrepaired muscle cells in aging tissue. About 40% of the human body mass is comprised of skeletal muscle, which indicates that the satellite cells contribute significantly to the total number of cells in humans. Hence, impaired satellite cell function due to the dysregulation of transcriptional and epigenetic activator effectors will have a major impact on the overall aging in humans because of the altered activities of extrinsic and intrinsic factors during muscle cell aging. However, results from studies regarding aged satellite cell function in a mimicked young environment are contentious, as interactive signaling pathways associated with both extrinsic and intrinsic factors are altered during aging. Therefore, a comprehensive understanding of all the extrinsic and intrinsic factors or mechanisms/pathways that are altered during muscle cell aging is required to enhance our knowledge on aging and develop potential novel therapeutics to slow the effects of aging. In this chapter, we focus our discussion on skeletal muscle and its satellite cell function, and the role played by extrinsic and intrinsic factors in the regulation of their gene expression, metabolism, signaling pathway or epigenetics, and their altered regulations during aging.

Begomoviruses belong to the family Geminiviridae are single-stranded circular DNA viruses with either monopartite (DNA-A genome of about 2.7 kb), encoding six open reading frames or bipartite genomes (DNA-A and DNA-B genomes of 2.5–2.6 kb) encapsulated in twinned particles. They are efficiently transmitted by the vector whitefly (Bemisia tabaci) to dicotyledonous plants. The DNA-A component of the bipartite begomoviruses is involved in replication and production of virions, but requires the DNA-B component for nuclear localization, systemic infection, host-range determination, and symptom expression. Begomoviruses are known to have satellite molecules known as betasatellites and alphasatellites. Plant virology in Saudi Arabia is in its infancy; very little information is available about the plant viruses causing diseases in important crops. This chapter summarizes the major developments and current status of begomovirus research and future prospects, especially in the area of begomovirus research, in Saudi Arabia.

SUN proteins participate in diverse cellular activities, many of which are connected to the nuclear envelope. Recently, the family member SUN1 has been linked to novel biological activities. These include the regulation of nucleoli, intranuclear compartments that assemble ribosomal subunits. We show that SUN1 associates with nucleoli in several mammalian epithelial cell lines. This nucleolar localization is not shared by all cell types, as SUN1 concentrates at the nuclear envelope in ganglionic neurons and non-neuronal satellite cells. Database analyses and Western blotting emphasize the complexity of SUN1 protein profiles in different mammalian cells. We constructed a STRING network which identifies SUN1-related proteins as part of a larger network that includes several nucleolar proteins. Taken together, the current data highlight the diversity of SUN1 proteins and emphasize the possible links between SUN1 and nucleoli. Keywords: Nucleus, Nucleolus, Nuclear envelope, SUN1

This paper provides in vitro phenotypical data to show that APOBEC2, a member of apoB mRNA editing enzyme, catalytic polypeptide-like family, may implicate in self-renewal functions of myogenic stem satellite cells, namely in the re-establishment of quiescent status after activation and proliferation of myoblasts in single-myofiber culture.

Satellite cells (SCs) form the resident stem cell population in the skeletal muscle tissue. While their function in mediating tissue regeneration after injury is well described, their role in the undamaged-, aging-, and exercising muscle is only starting to be unraveled. Although direct evidence linking the loss of SC function to the onset of age-related loss of muscle mass and function (i.e., sarcopenia) is currently lacking, satellite cells are increasingly seen as an important component for the decline of tissue function seen with aging. This is evident from the pertinent role of SCs in maintaining homeostasis, and in mediating remodeling- and repair-responses, in the skeletal muscle. This narrative review focuses on human studies, but includes cellular and animal models, to describe the role of SCs in different physiological scenarios relevant for human aging. The intrinsic and extrinsic mechanisms underlying age-induced alterations in the SC pool are discussed, with particular emphasis on the genomic modifications that accumulate in human SCs during a lifetime (i.e., somatic mutation-burden). Finally, the role of exercise as a potential countermeasure to age-induced SC alterations is explored in the different scenarios covered.

Adult skeletal muscle is endowed with regenerative potential through partially recapitulating the embryonic developmental program. Upon acute injury or in pathological conditions, quiescent muscle-resident stem cells, called satellite cells, become activated and give rise to myogenic progenitors that massively proliferate, differentiate, and fuse to form new myofibers and restore tissue functionality. In addition, a proportion of activated cells returns back to quiescence and replenish the pool of satellite cells in order to maintain the ability of skeletal muscle tissue to repair. Self-renewal is the process by which stem cells divide to make more stem cells to maintain the stem cell population throughout life. This process is controlled by cell-intrinsic transcription factors regulated by cell-extrinsic signals from the niche and the microenvironment. This chapter provides an overview about the general aspects of satellite cell biology and focuses on the cellular and molecular aspects of satellite cell self-renewal. To date, we are still far from understanding how a very small proportion of the satellite cell progeny maintain their stem cell identity when most of their siblings progress through the myogenic program to construct myofibers.

Our understanding of satellite cells, now known to be the obligate stem cells of skeletal muscle, has increased dramatically in recent years due to the introduction of new molecular, genetic, and technical resources. In addition to their role in acute repair of damaged muscle, satellite cells are of interest in the fields of aging, exercise, neuromuscular disease, and stem cell therapy, and all of these applications have driven a dramatic increase in our understanding of the activity and potential of satellite cells. However, many fundamental questions of satellite cell biology remain to be answered, including their emergence as a specific lineage, the degree and significance of heterogeneity within the satellite cell population, the roles of their interactions with other resident and infiltrating cell types during homeostasis and regeneration, and the relative roles of intrinsic vs extrinsic factors that may contribute to satellite cell dysfunction in the context of aging or disease. This review will address the current state of these open questions in satellite cell biology.

The regenerative capacity of skeletal muscle is due to a population of satellite cells known as satellite stem cells. Owing to their ability to generate both stem cells and committed myogenic progenitors, satellite stem cells allow self-renewal of the satellite cell reservoir and provide myogenic progenitor cells to repair the muscle tissue. Increasing numbers of studies have highlighted the indispensable role of the niche in the regulation of the stem cell functions. The niche maintains the muscle stem cell in a quiescent state but in response to muscle injury, the niche actively generates signals for satellite cell activation, proliferation, and differentiation. The cross talk between the muscle stem cell and its niche is critical and alterations of the niche components result in defective regeneration and muscle pathologies. Here, we describe how the satellite cell niche regulates satellite cell functions, namely commitment and self-renewal, in resting, injured, and pathologic muscle.

Satellite viruses (SVs) are subviral pathogens that are entirely dependent upon the replication machinery of their helper viruses. There are only four known plant SVs: satellite tobacco necrosis virus, satellite tobacco mosaic virus, satellite panicum mosaic virus, and satellite maize white line mosaic virus. These SVs have positive-sense single-stranded RNA genomes of 800–1400 nt that are encapsidated within ~17-nm T =1 icosahedral virions. SVs, in contrast to satellite-RNA or -DNA, encode a capsid protein for independent genome packaging of the cognate SV RNA. The unusually small and compact nature of these subviral agents has resulted in their use as models for fundamental virology studies, including gene expression, genome packaging, and virion structure.

Sulf1A expression, which is a characteristic of embryonic muscle, is undetectable in mature muscle fibres and quiescent satellite cells, but is re-activated in vivo upon injury and in vitro following activation of satellite cells. Sulf1A is known to enhance canonical Wnt signalling, and its association with Wnt1-induced satellite cell proliferation in vitro in the present study further confirmed this. However, exogenous Wnt6 decreased satellite cell proliferation but promoted the adoption of a hyper-elongated cell morphology in myoblasts on isolated single fibres in culture. Such Wnt6-induced cellular hyper-elongation and inhibition of proliferation was found to be dependent upon Sulf1A, as treatment with Sulf1A neutralising antibodies abolished both these effects. This indicates that Sulf1A can regulate Wnt6 signalling and cellular differentiation in skeletal muscle., Highlights: ▸ Sulf1 regulates not only Wnt1 but also Wnt6 signalling. ▸ Wnt1 and Wnt6 play contrasting roles in skeletal muscle growth regulation. ▸ Reduction in Sulf1 activity level can reverse Wnt6-induced myogenic differentiation.

According to industry analysts, more than 4,500 satellites will be in orbit by the year 2016. The implications of the continuing boom in satellites are revolutionary for those who did not have access to secure encrypted data in remote locations around the world. This chapter discusses how encryption algorithms will play a key role in the next stage of development for advanced virtual satellite systems that promise to replace monolithic satellites with clusters of wirelessly-interconnectd satellite modules. In addition to satellite encryption use by commercial organizations and governments, this chapter presents the implementation of a secure encrypted wireless environment encompassing direct satellite communications and land-based communications links. An information assurance/cybersecurity architecture that supports the sharing of common resources across multiple payloads/users at multiple encryption levels is also covered. In addition, the following are also coverered: The role of satellite encryption technology trends with regards to the pace that the national cryptography policy must keep up with; the political environment; and, the significant changes in the post-Cold War environment that call attention to the need for and the impact a cryptography policy would have domestically and internationally. Furthermore, the book describes the instruments and goals of the current U.S. satellite encryption policy and some of the issues raised by current policy. In general, the chapter covers the development, implementation and management of advanced satellite encryption options and strategies that will forever change how organizations do business now and in the foreseeable future. Also, the chapter discusses the misuse of satellite encryption technology by the government; the international community; international and domestic terrorist organizations; and, domestic and international criminal organizations. The chapter further evaluates enlarging the space of possible satellite encryption policy options, and offers findings and recommendations. This chapter will leave little doubt that a new world infrastructure in the area of encrypted satellite communications is about to be constructed. The text will benefit organizations and governments, as well as their advanced citizens. For the disadvantaged regions of the world, however, advanced satellite encryption communications could be one of those rare technological events that enable traditional societies to leap ahead and long-dormant economies to flourish in security.

This chapter discusses satellite cyber attacks with regard to hacking, interference, and jamming. For the past several years, we have been notified that sunspot activity could disrupt Earth’s communications. In fact, there have been numerous cell phone outages owing to sunspots. This disruption has a significant impact on the daily life of humans on this planet. Nearly all disruptions we have experienced have been the result of natural acts. Imagine if someone had the capability to hack a satellite. This type of activity appears in movies: Hackers release malicious software installed on a system that modifies the geographic positioning system of oceangoing oil tankers. Although this potentiality may be unrealistic, if it occurred, the effect would be extremely high. Whether environmental disaster, total disruption of command-and-control of a military operation, or massive outages of satellite connectivity during the Super Bowl, the impacts would be significant relative to sunspots.

The molecular biology, epidemiology, and evolutionary dynamics of Pepino mosaic virus (PepMV) are much better understood than those of Tomato torrado virus (ToTV). The earliest descriptions of PepMV suggest a recent jump from nontomato species (e.g., pepino; Solanum muricatum) to tomato (Solanum lycopersicum). Its stability in contaminated plant tissues, its transmission through seeds, and the global trade of tomato seeds and fruits may have facilitated the global spread of PepMV. Stability and seed transmission also probably account for the devastating epidemics caused by already-established PepMV strains, although additional contributing factors may include the efficient transmission of PepMV by contact and the often-inconspicuous symptoms in vegetative tomato tissues. The genetic variability of PepMV is likely to have promoted the first phase of emergence (i.e., the species jump) and it continues to play an important role as the virus becomes more pervasive, progressing from regional outbreaks to pandemics. In contrast, the long-term progression of ToTV outbreaks is not yet clear and this may reflect factors such as the limited accumulation of the virus in infected plants, which has been shown to be approximately two orders of magnitude less than PepMV. The efficient dispersion of ToTV may therefore depend on dense populations of its principal vectors, Bemisia tabaci and Trialeurodes vaporariorum, as has been proposed for the necrogenic satellite RNA of Cucumber mosaic virus.

The L-A virus of Saccharomyces cerevisiae is a single-segment 4.6 kbp double-stranded (dsRNA) virus encoding only a major coat protein (‘Gag’, with an mRNA-decapping activity) and an RNA-dependent RNA polymerase (Pol), made as a Gag–Pol fusion protein using a –1 ribosomal frameshift mechanism. L-A has an entirely intracellular life cycle with a conservative replication mechanism. An internal RNA packaging site, and replication sites internal and at the 3′ end have been defined. L-A supports the replication of any of several satellite dsRNAs, called M1, M2, and M28, encoding secreted toxins (‘killer’ toxins). The icosahedral virions have 120 Gag molecules, arranged as 60 copies of an asymmetric dimer, and 2 Gag–Pol molecules. The outer virion surface includes an mRNA-decapping activity that transfers the 5′ cap structure of cellular mRNAs to His154 of Gag. This activity is required for normal expression of viral mRNAs which lack 5′ cap and 3′ polyA structures, probably by making decapped derivatives of cellular mRNAs to decoy the Xrn1 exoribonuclease that specifically degrades uncapped mRNAs. The cellular Ski proteins block translation of viral and other non-polyA mRNAs, and promote their degradation. Mak3p is a cellular N-acetyltransferase whose modification of Gag is necessary for viral assembly.

Viruses belonging to the family Partitiviridae usually cause cryptic infections in fungi and plants, and are classified into three genera, Partitivirus, Alphacryptovirus, and Betacryptovirus. The genus Partitivirus consists of viruses that infect filamentous fungi. The genera Alphacryptovirus and Betacryptovirus include viruses that are found in plants. Over 20 fungal virus (mycovirus) species have been identified or tentatively identified as members of the genus Partitivirus. The name Partitiviridae originates from the Latin partitus, which means ‘divided’ due to the fact that the genome of these viruses is bipartite (separately encapsidated) and consists of two linear monocistronic dsRNAs. Viruses of the genus Partitivirus have isometric particles with icosahedral symmetry ranging from 30 to 35 nm in diameter. The virion capsid is not enveloped and consists of 12 capsomers and 120 capsid protein (CP) subunits. The two genomic dsRNA components of partitiviruses are 1.5–2.4 kbp in size. Additional dsRNAs (satellite or defective) may be present in purified partitivirus particles. The larger dsRNA component encodes a virion-associated RNA-dependent RNA polymerase (size range 77–86 kDa), whereas the smaller dsRNA encodes the CP (size range 57–76 kDa).

Cucumber mosaic virus (CMV) is the type member of the genus Cucumovirus in the family Bromoviridae. CMV has a worldwide distribution and a host range of over 1300 plant species. The virus is transmitted by about 80 species of aphid in a nonpersistent manner. CMV is also transmitted through the seed with variable, but usually low, efficiencies. The CMV genome consists of three, single-stranded, positive-sense RNAs, encoding five proteins. The three genomic RNAs are packaged separately into isometric particles of 29 nm diameter (T = 3 symmetry), while RNA3 is co-packaged with subgenomic RNA4. The 1a and 2a proteins are involved primarily in virus replication occurring on tonoplast membranes, while the 2b, 3a, and 3b (capsid) proteins are involved in virus movement. The 2b protein is an inhibitor of plant defense responses. Different isolates of CMV induce a variety of disease responses, which are attenuated by a satellite RNA associated with some isolates of CMV, although some satellite RNAs can enhance pathogenicity. Control of CMV has been achieved to a limited extent by use of transgenic plants expressing viral sequences, but due to the considerable sequence diversity of this virus, natural resistance genes do not give broad-spectrum resistance.

Gene sequencing was invented in the 1980s, enabling the evolutionary relationships of organisms to be studied in detail. The ways in which these studies provide the intellectual framework for research into the life of viruses continues to expand. Plants, animals and other organisms present viruses with very different environments, both structurally and biochemically, and this may be the reason why so few virus groups span host kingdoms, but a few do, and studies of these reveal the shared and unique constraints and opportunities provided by different types of host, and also the diverse ways that viruses overcome the constraints. The RNA-silencing system seems to provide the primary plant defense against viruses, and although RNA-silencing mechanisms are present in all eukaryotes, they are most developed in plants where they also modulate the expression of plant genes. Plants have a rigid cellular structure with the cells connected by plasmodesmata too narrow for virions to pass through. This has required viruses to adopt specific mechanisms to aid their systemic spread within plants. The diverse measures adopted by viruses to suppress RNA silencing and to aid their spread through plants indicate that such mechanisms have evolved independently on several occasions. Likewise a great range of symbiotic, commensal, and satellite relationships are found among plant viruses, and again the diversity of the relationships, of the virus groups involved, and of the resulting phenotypes, emphasizes that viruses of plants are polyphyletic. Studies of mutations in model experimental systems, and of gene sequence variation in natural viral populations, are clarifying the mechanisms that produce “quasispecies,” even though the concept seems to be still largely misunderstood. The relative contribution of different evolutionary processes, including mutation, drift, recombination, and selection, to viral population change is becoming better understood. The taxonomies of tobamoviruses and of their principle hosts seem to be congruent, indicating that they have probably co-evolved, and hence may be of the same age, around 100 million years. However potyviruses and their hosts show no such relationships, indeed gene sequence differences in viral populations, of which the history is known, indicate that the genus Potyvirus may be only a few thousand years old. Our understanding of more distant relationships remains very speculative as it depends on comparisons of “molecular phenotypic” characters (e.g. structure and function) rather than of gene sequences. Viruses have been studied for more than a century, their molecules are well known, but our understanding of the molecular basis of plant virus biology is still in its infancy, and we have little idea of how viruses will respond to “climate change” and “transgene pollution.”

Banana bunchy top virus (BBTV, genus Babuvirus, family Nanoviridae) causes the most destructive viral disease of banana worldwide, but is restricted to some countries in Africa and the Asia-Pacific region. Hosts of the virus are found only in the plant family Musaceae, and it is transmitted through vegetative planting material and in a circulative, nonpropagative manner by its sole vector the banana aphid (Pentalonia nigronervosa). In banana, disease symptoms include stunting, leaf chlorosis, and rosetting, and a cessation of fruiting, and no natural source of immunity is known. Histological effects and virus replication are restricted to the phloem tissue. The virus has isometric virions, 18–20 nm in diameter, separately encapsidating each of the six integral circular single-stranded DNA (ssDNA) genome components. All components are monocistronic, except for DNA-R, which encodes the master replication initiation protein, and a smaller internal open reading frame (ORF) of unknown function. Replication is via a rolling-circle mechanism, and the genome components share two conserved areas in their respective untranslated regions; the stem loop common region that contains the origin of replication and the major common region which binds a heterogeneous population of DNA primers, around 80 nt in length, that prime complementary strand synthesis.

Bringing Discovery to Light — Proceedings of an official satellite symposium at the 13th European Cancer Conference (ECCO), Paris, 2005.-- Proceedings of an official satellite symposium at the 13th European Cancer Conference.-- Open Access.

Slender projections, similar to microvilli, are the main specialization of the perikaryal surface of sensory ganglion neurons. The extent of these projections correlates closely with the volume of the corresponding nerve cell body. It is likely that the role of perikaryal projections of sensory ganglion neurons, which lack dendrites, is to maintain the surface-to-volume ratio of the nerve cell body above some critical level for adequate metabolic exchange. Satellite cells probably have the ability to promote, or provide a permissive environment for, the outgrowth of these projections. It is not yet known whether the effect of satellite cells is mediated by molecules associated with their plasma membrane or by diffusible factors. Furthermore, receptor molecules for numerous chemical agonists are located on the nerve cell body surface, but it is not known whether certain molecules are located exclusively on perikaryal projections or are also present on the smooth surface between these projections. Further study of the nerve cell body surface and of the influence that satellite cells exert on it will improve our understanding of the interactions between sensory ganglion neurons and satellite neuroglial cells.

msDNAs are small, structurally unique satellite DNAs found in a number of Gram-negative bacteria. Composed of hundreds of copies of single-stranded DNA—hence the name multicopy single-stranded DNA—msDNA is actually a complex of DNA, RNA, and probably protein. These peculiar molecules are synthesized by a reverse transcription mechanism catalyzed by a reverse transcriptase (RT) that is evolutionarily related to the polymerase found in the HIV virus. The genes, including the RT gene, responsible for the synthesis of msDNA are encoded in a retron, a genetic element that is carried on the bacterial chromosome. The retron is, in fact, the first such retroelement to be discovered in prokaryotic cells. This report is a comprehensive review of the many interesting questions raised by this unique DNA and the fascinating answers it has revealed. We have learned a great deal about the structure of msDNA: how it is synthesized, the structure and functions of the RT protein required to make it, its effects on the host cell, the retron element that encodes it, its possible origins and evolution, and even its potential usefulness as a practical genetic tool. Despite the impressive gains in our understanding of the msDNAs, however, the simple, fundamental question of its natural function remains an enduring mystery. Thus, we have much more to learn about the msDNAs of bacteria.

International audience; The characteristics of fish satellite cells in situ and in vitro are described. The in situ proliferation of satellite cells appears to be very low and therefore not easy to quantify. Differences in the in vitro proliferation capacities of satellite cells have been observed between species, but a large part of these differences could be related to methodology. Most studies on fish satellite cells have been carried out on cyprinids and salmonids. The relationship between proliferation capacity and muscle growth is discussed in these fish. The differentiation of fish satellite cells is partially similar to that of myobJasts. However, there is a great heterogeneity in satellite cell differentiation that needs to be characterized.

Publisher Summary This chapter focuses on the second viroid family, whose members are also referred to as hammerhead viroids, taking into account their most outstanding feature. If the word “small” is the first to come to mind when considering viroids, perhaps the second word is “hammerhead,” because this class of ribozymes, which because of its structural simplicity has an enormous biotechnological potential, is described in avocado sunblotch viroid (ASBVd) as well as in a viroid-like satellite RNA. The most outstanding feature of the Avsunviroidae members is their potential to adopt hammerhead structures in both polarity strands and to self-cleave in vitro accordingly. Viroids differ from viruses not only in their genome size but also in other fundamental aspects, prominent among which is the lack of messenger activity of both viroid RNAs and their complementary strands.

Publisher Summary This chapter focuses on the cause of rosette disease of groundnut in which the umbravirus groundnut rosette virus (GRV) depends on groundnut rosette assistor virus (GRAV) for transmission by Aphis craccivora . The GRV/GRAV complex is, especially interesting, because the main cause of rosette disease symptoms in groundnut is a third component, a satellite RNA, which depends on GRV for its replication but on GRAV for its encapsidation and transmission by aphids. There are two major symptom variants, chlorotic rosette and green rosette with considerable variation within each type. Both the chlorotic and green forms of the disease make plants severely stunted, with shortened internodes and reduced leaf size. In chlorotic rosette, the leaves are bright yellow, usually with a few green islands. The biological properties of GRAV, which replicates autonomously in plants, are typical of a luteovirus and GRAV is therefore classified within the family Luteoviridae .

Publisher Summary Much progress is made in all spheres of understanding of hepatitis B virus (HBV) and its associated diseases. This chapter takes a look at recent findings, which pave the way to future research into this medically important virus. Recent developments include the three-dimensional structure of core particles and further elucidation of the antigenic structure of hepatitis B surface antigen (HBsAg). Knowledge of the structure is important for the analysis of antigenic variants, which are found in a number of clinical situations. Hepatitis D virus is the only virus in the satellite family known to infect animal species. Recently, the world map of prevalence of HDV is modified, with decreasing prevalence in certain areas and some new foci of HDV endemicity. Cirrhosis is common in chronic HDV. Diagnosis is by detection of HDV antigens, antibodies, or RNA in serum. Although dot-blot hybridization is useful, the sensitivity of the polymerase chain reaction (PCR) is superior further, PCR correlated with intrahepatic HDAg detection.

Publisher Summary Skeletal muscle satellite cell culture techniques have provided a means for coupling muscle structural and physiological observations to cellular and molecular explanations. Intrinsic properties of these myogenic cells have been studied in vitro , and it has become apparent that the satellite cell has properties that are distinctly different from those of embryonic or fetal myogenic cells. This chapter describes two types of satellite cell culture procedures—(1) monolayer mass cultures of dissociated satellite cells and (2) single muscle fiber cultures with their associated satellite cells—and discusses their application. In both cases, cells and fibers are isolated directly from experimental subjects. The general cellular processes that have been studied in satellite cell culture systems include activation from the quiescent state, migration, proliferation, and differentiation or return to quiescence. There are advantages and disadvantages to each of the culture systems and one single culture system may not be adequate for addressing all experimental questions.

Satellite DNAs from normal mouse tissues and from Ehrlich ascites tumor cells (EAT) were compared with respect to: 1. Thermal stability of duplexes formed upon homologous (mousexmouse) and heterologous (mouse x EAT) reassociation of isolated heavy (H) and light (L) strands of the corresponding satellite DNAs. 2. Restriction pattern of the satellite DNAs treated with 10 different restriction endonucleases. No differences were found. The negative results indicate that the considerable evolution of the Ehrlich ascites tumor (both in biological properties and in karyotype) has not been accompanied by alterations in the satellite DNA which could be detected by the methods used. The relatively high conservatism of the satellite DNA during progression of transplantable tumors suggests that satellite DNA may play a vital role in some universal cellular functions, possibly connected with cell proliferation.