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Maintenance of indeterminacy is fundamental to the generation of plant architecture and a central component of the plant life strategy. Indeterminacy in plants is a characteristic of shoot and root meristems, which must balance maintenance of indeterminacy with organogenesis. The Petunia hybrida HAIRY MERISTEM (HAM) gene, a member of the GRAS family of transcriptional regulators, promotes shoot indeterminacy by an undefined non-cell-autonomous signaling mechanism(s). Here, we report that Arabidopsis (Arabidopsis thaliana) mutants triply homozygous for knockout alleles in three Arabidopsis HAM orthologs (Atham1,2,3 mutants) exhibit loss of indeterminacy in both the shoot and root. In the shoot, the degree of penetrance of the loss-of-indeterminacy phenotype of Atham1,2,3 mutants varies among shoot systems, with arrest of the primary vegetative shoot meristem occurring rarely or never, secondary shoot meristems typically arresting prior to initiating organogenesis, and inflorescence and flower meristems exhibiting a phenotypic range extending from wild type (flowers) to meristem arrest preempting organogenesis (flowers and inflorescence). Atham1,2,3 mutants also exhibit aberrant shoot phyllotaxis, lateral organ abnormalities, and altered meristem morphology in functioning meristems of both rosette and inflorescence. Root meristems of Atham1,2,3 mutants are significantly smaller than in the wild type in both longitudinal and radial axes, a consequence of reduced rates of meristem cell division that culminate in root meristem arrest. Atham1,2,3 phenotypes are unlikely to reflect complete loss of HAM function, as a fourth, more distantly related Arabidopsis HAM homolog, AtHAM4, exhibits overlapping function with AtHAM1 and AtHAM2 in promoting shoot indeterminacy.

To date, the trout B-cell is poorly defined, as many essential molecular markers are not yet available for this species. In mammalian systems, the transcription factor Pax5, expressed from pre-B through plasmablast stages, provides an important marker for B-cell differentiation. In a previous study we showed that Pax5 is expressed in the trout. Here we identify trout B-cell populations that vary in expression of Pax5, membrane and secreted Ig. Immune tissues were separated based on concentration of surface IgM, and analyzed by qPCR and flow cytometry. Results suggest that spleen and PBL contain mostly resting B cells, which lack secreted Ig. While the great majority of splenic B cells become strongly activated upon LPS stimulation, PBLs do not. Additionally, anterior kidney contains both developing B and Ig-secreting B-cell populations, but few resting, mature B cells. Lastly, posterior kidney contains multiple B-cell populations in various states of activation. We conclude that trout immune tissues contain multiple, developmentally diverse and tissue-specific B-cell populations as defined by their relative expression of Pax5, surface IgM, and secreted IgM.

Restriction and modification (R-M) systems are generally thought to protect bacteria from invasion by foreign DNA. This paper proposes the existence of an alternative role for the phase-variable R-M systems encoded by the hsd loci of Mycoplasma pulmonis. Populations of M. pulmonis cells that arose during growth in different environments were compared with respect to R-M activity and surface antigen production. When M. pulmonis strain X1048 was propagated in laboratory culture medium, > 95% of colony-forming units (cfu) lacked R-M activity and produced the variable surface protein VsaA. Mycoplasmas isolated from the nose of experimentally infected rats also lacked R-M activity and produced VsaA. In contrast, the cell population of mycoplasmas isolated from the lower respiratory tract of the infected rats was more complex. The most dramatic results were obtained for mycoplasmas isolated from the trachea. At 14 days postinfection, 38% of mycoplasma isolates produced a Vsa protein other than VsaA, and 34% of isolates had active restriction systems. These data suggest that differences in selection pressures in animal tissues affect the surface proteins and the R-M activity of the mycoplasmal cell population. We propose that variations in the production of R-M activity and cell surface proteins are important for the survival of the mycoplasma within the host.

The vsa genes of Mycoplasma pulmonis encode the V-1 lipoproteins. Most V-1 proteins contain repetitive domains and are thought to be involved in mycoplasma-host cell interactions. Previously, we have reported the isolation and characterization of six vsa genes comprising a 10-kb region of the genome of M. pulmonis strain KD735-15. In the current study, vsa -specific probes were used to clone several fragments from a genomic library of KD735-15 DNA and assemble a single 20-kb contig containing 11 vsa genes. The middle region of the vsa locus contains a large open reading frame (ORF) that is not a vsa gene and has undergone an internal deletion in some strains. The ORF is predicted to encode a membrane protein that may have a role in disease pathogenesis. To examine vsa genes in a strain of M. pulmonis that is unrelated to KD735-15, strain CT was studied. Through Southern hybridization and genomic cloning analyses, CT was found to possess homologs of the KD735-15 vsaA , - C , - E , and - F genes and two unique genes ( vsaG and vsaH ) that were not found in KD735-15. High-frequency, site-specific DNA inversions serve to regulate the phase-variable production of individual V-1 proteins. As a result of the sequence analysis of vsa recombination products, a model in which DNA inversion arises from strand exchange involving at least six nucleotides of the vrs box is proposed.

Germline stem cells (GSCs) in Drosophila are descendants of primordial germ cells (PGCs) specified during embryogenesis. The precise timing of GSC establishment in the testis has not been determined, nor is it known whether mechanisms that control GSC maintenance in the adult are involved in GSC establishment. Here, we determine that PGCs in the developing male gonad first become GSCs at the embryo to larval transition. This coincides with formation of the embryonic hub; the critical signaling center that regulates adult GSC behavior within the stem cell microenvironment (niche). We find that the Jak–STAT signaling pathway is activated in a subset of PGCs that associate with the newly-formed embryonic hub. These PGCs express GSC markers and function like GSCs, while PGCs that do not associate with the hub begin to differentiate. In the absence of Jak–STAT activation, PGCs adjacent to the hub fail to exhibit the characteristics of GSCs, while ectopic activation of the Jak–STAT pathway prevents differentiation. These findings show that stem cell formation is closely linked to development of the stem cell niche, and suggest that Jak–STAT signaling is required for initial establishment of the GSC population in developing testes.

As the major excitatory neurotransmitter in the vertebrate nervous system, glutamate not only plays an essential role in adult neural signaling, but has also been implicated as a trophic factor in neuronal cell maturation, differentiation, and survival. An essential component of the glutamatergic neurotransmission system is the family of glutamate transporters, a multigene family that codes for plasma membrane-bound as well as vesicle-bound proteins responsible for the removal of glutamate from the cleft and its re-uptake into the synaptic vesicle. Here we describe the spatial and temporal expression of the vesicular glutamate transporter (xVGlut1) during the early developmental stages of the amphibian Xenopus laevis. RNAse protection analysis and in situ hybridization reveal that xVGlut1 is first expressed at late neurula stages in the developing spinal cord and trigeminal nerve. By tailbud stages xVGlut1 transcripts are detected in several of the cranial nerves, the pineal gland, and medial forebrain. By hatching stages xVGlut1 expression reappears in localized tracts within the spinal cord. Expression levels increase throughout development into adulthood.