Search

It is possible that the reproductive strategy of the short-beaked echidna is related to seasonal changes in fat deposition and energy availability, regulated by seasonal changes in endocrine function. We predicted that circulating leptin levels would be directly proportional to adiposity during most of the year, but that a change in this relationship would occur during the pre-breeding season to allow increased fat deposition. To test this hypothesis, we made use of a captive colony of echidnas to describe and quantify changes in fat distribution and the adipostatic hormone leptin. First we assessed seasonal changes in circulating leptin levels, body mass and adiposity for three male and three female adult echidnas maintained on a standard diet. Second, we explored the relationship between circulating leptin levels and increased caloric intake for an additional five adult female echidnas that were provided with supplemented nutrition. Third we visualised fat distribution in male and female adult echidnas using magnetic resonance imaging (MRI) before and after the breeding season, to determine where fat is deposited in this species. For echidnas maintained on the standard diet, there were no seasonal changes in body mass, body fat or plasma leptin levels. However, female echidnas provided with supplemented nutrition had significantly elevated plasma leptin levels during the breeding season, compared to the pre-and post- breeding periods. MRI showed substantial subcutaneous fat depots extending dorso-laterally from the base of the skull to the base of the tail, in both sexes. Pre-breeding season, both sexes had considerable fat deposition in the pelvic/rump region, whilst the female echidna accumulated most fat in the abdominal region. This study shows that male and female echidnas accumulate body fat in the pelvic/rump and the abdominal regions, respectively and that circulating leptin may promote fattening in female echidnas during the breeding season by means of leptin resistance. However, further research is required to evaluate the precise relationship between seasonal changes in leptin and adiposity. [ABSTRACT FROM AUTHOR]

Monotremes (echidnas and platypus) possess five X and four or five Y sex chromosomes, respectively, that evolved independently from the sex chromosomes found in therian mammals. While the platypus has obvious venomous spurs in the male, the short-beaked echidna (Tachyglossus aculeatus) lacks easily identifiable sexually dimorphic characteristics, making it difficult to sex adults out of the breeding season and almost impossible to sex juveniles or embryonic material. Here, we used restriction-site associated DNA sequencing (RADseq) to identify novel sex-specific markers in the short-beaked echidna. We identified and validated a subset of male-specific markers that can be used as a non-invasive genetic sex test for the short-beaked echidna. We also assessed how laboratory conditions, including DNA extraction protocol and number of PCR cycles, can influence the outcome of genetic sex tests. The combined use of these markers will provide a valuable toolkit for researchers, conservationists, and zoo-keepers to reliably and non-invasively determine sex in the short-beaked echidna. [ABSTRACT FROM AUTHOR]

The composition of milk includes factors required to provide appropriate nutrition for the growth of the neonate. However, it is now clear that milk has many functions and comprises bioactive molecules that play a central role in regulating developmental processes in the young while providing a protective function for both the suckled young and the mammary gland during the lactation cycle. Identifying these bioactives and their physiological function in eutherians can be difficult and requires extensive screening of milk components that may function to improve well-being and options for prevention and treatment of disease. New animal models with unique reproductive strategies are now becoming increasingly relevant to search for these factors. [ABSTRACT FROM AUTHOR]

The article presents information on the function of milk in the mammalian species with respect to the monotremes and marsupial species. It mentions the process of milk secretion in the mammals and highlights the role of milk in different physiological functions inside the body including organs development, mammary gland proliferation or apoptosis, and antimicrobials protection to the young infants. It mentions the lactation process in the animals with respect to the reproductive adaptations.

Natural killer (NK) cells affect a form of innate immunity that recognizes and eliminates cells that are infected with certain viruses or have undergone malignant transformation. In mammals, this recognition can be mediated through immunoglobulin- (Ig) and/or lectin-type NK receptors (NKRs). NKR genes in mammals range from minimally polymorphic single-copy genes to complex multigene families that exhibit high levels of haplotypic complexity and exhibit significant interspecific variation. Certain single-copy NKR genes that are present in one mammal are present as expanded multigene families in other mammals. These observations highlight NKRs as one of the most rapidly evolving eukaryotic gene families and likely reflect the influence of pathogens, especially viruses, on their evolution. Although well characterized in human and mice, cytotoxic cells that are functionally similar to NK cells have been identified in species ranging from birds to reptiles, amphibians and fish. Although numerous receptors have been identified in non-mammalian vertebrates that share structural relationships with mammalian NKRs, functionally defining these lower vertebrate molecules as NKRs is confounded by methodological and interpretive complexities. Nevertheless, several lines of evidence suggest that NK-type function or its equivalent has sustained a long evolutionary history throughout vertebrate species. [ABSTRACT FROM AUTHOR]

Complementary DNAs encoding immunoglobulin light chains were isolated from two monotreme species, Ornithorhynchus anatinus (duckbill platypus) and Tachyglossus aculeatus (echidna). The sequences of both the variable and constant regions of these clones had greater similarity to IGK than to other light chain classes and phylogenetic analyses place them squarely within the mammalian IGK group, establishing them as monotreme IGK homologues. The constant region sequences of all clones were essentially identical within each species and, along with Southern blot results, the data are consistent with a single IGKC in each species. The expressed IGKV repertoires from both platypus and echidna were randomly sampled and there appear to be at least four platypus and at least nine echidna IGKV subgroups. The IGKV subgroups are highly divergent within species, in some cases sharing as little as 57% nucleotide identity. Two of the IGKV subgroups are present in both species, so there is some degree of overlap in the germline repertoires of these two monotremes. Overall the complexity seen in platypus and echidna IGK light chains is comparable with that of other mammals considered to have high levels of germline diversity and is in contrast to what has been found so far for monotreme IGL. [ABSTRACT FROM AUTHOR]

Monotremes are an ancient mammalian lineage that last shared a common ancestor with the marsupial and eutherian (placental) mammals about 170 million years ago. Characterization of their immune genes is allowing us to gain insights into the evolutionary processes that lead to the ‘mammalian’ immune response. Here we describe the characterization of the first cDNA clones encoding T-cell receptors from a monotreme. Two TCR α-chain cDNAs (TCRA) from the short-beaked echidna, Tachyglossus aculeatus, containing complete variable, joining and constant regions were isolated. The echidna TCRA constant region shares approximately 37% amino acid identity with other mammalian TCRA constant region sequences. The two variable regions belong to the TCRAV group C, which also contains V genes from humans, mice, cattle and chickens. One echidna TCR β-chain cDNA (TCRB) containing the entire constant region was isolated and sequenced. It shares about 63% identity with other mammalian TCRB constant region sequences. The echidna TCRBV belongs to TCRBV group A, which also contains V genes from various eutherian species. Southern blot analysis indicates that, like in other mammalian species, there is only one TCRA constant region copy in the echidna genome, but at least two TCRB constant regions. [ABSTRACT FROM AUTHOR]

Extant mammals are composed of three lineages: the eutherians, the marsupials and the monotremes. The majority of the mammalian major histocompatibility complex (MHC) data is based on the eutherian mammals, which generally have three classical MHC class II β chain gene clusters — DRB, DQB and DPB, as well as the non-classical DMB and DOB. Marsupial DMB, DAB and DBB have been characterised. Confusion still surrounds the relationship of the marsupial DAB and DBB genes with the classical eutherian class II clusters. Here we present the first monotreme MHC class II β chain sequences. Four MHC class II β chain sequences were isolated from a spleen cDNA library from the short-beaked echidna , and one from a spleen cDNA library from platypus using a brushtail possum DAB probe. Given the non-orthologous relationship of the monotreme sequences with marsupial and eutherian β chain clusters, we recommend that the five new monotreme sequences be assigned the nomenclature 'DZB', signifying the description of a new mammalian β chain cluster. Our analysis suggests that all mammalian β chain sequences (except DMB) evolved from a common ancestor. Maximum likelihood analysis places the monotreme β chain sequences at the base of the mammalian clade, indicating their ancestral status. However, within the mammalian clade, monophyletic clades are not robust, and elucidation of the order of gene duplication that gave rise to the present-day gene clusters is not yet possible. [ABSTRACT FROM AUTHOR]

We report the isolation and characterization of cDNA clones of expressed, functional major histocompatibility complex class-I (Mhc-I) genes from two species of monotremes: the duck-billed platypus and the short-beaked echidna. The cDNA clones were isolated from libraries constructed from spleen RNA, clearly establishing their expression in at least this one peripheral lymphoid organ. From the presence of conserved amino acid residues, it appears the expressed sequences encode molecules that likely function as classical Mhc-I. These clones were isolated using monotreme Mhc-I processed pseudogenes as probes. These processed pseudogenes were isolated from genomic DNA and, based on their structure, are likely independently derived in the platypus and echidna. When all the monotreme sequences were included in phylogenetic analyses, we found no apparent orthologous relationships between the platypus and echidna Mhc-I. Analyses that included a large number of Mhc-I sequences from other taxa support a separate monotreme Mhc-I clade, basal to a therian Mhc-I clade that is comprised of sequences from marsupial and placental mammals. The phylogenies also support the hypothesis that Mhc-I genes of placental mammals, marsupials, and monotremes are derived from three separate lineages of Mhc-I genes, best explained by two rounds of duplications and deletions. The first round would have occurred prior to the divergence of monotremes and therians, and the second prior to the divergence of marsupials and placental mammals. The sequences described here represent the first reported functional monotreme Mhc-I, as well as the first processed pseudogenes of any type from monotremes. [ABSTRACT FROM AUTHOR]

A full-length immunoglobulin gamma clone from the echidna (Tachyglossus aculeatus) was isolated from a spleen cDNA library. The clone was 1,664 base pairs long and encoded the entire open reading frame, incorporating the V, D, J and C regions. The echidna clone had approximately 41% identity and 67% similarity at the amino acid level with both marsupial and eutherian IgG molecules. The presence of IgG in the monotremes confirms that the appearance of IgG occurred prior to the separation of the three extant mammalian lineages, but after their separation from the reptilian lineage, pinpointing the date to between 310 and 170 million years ago. Phylogenetic analyses using the immunoglobulin sequence data strongly support the 'Theria' hypothesis, with the monotreme lineage diverging prior to the separation of the marsupial and eutherian lineages. [ABSTRACT FROM AUTHOR]

The vertebrate mitochondrial genome is highly conserved in size and gene content. Among the chordates there appears to be one basic gene arrangement, but rearrangements in the mitochondrial gene order of the avian lineages have indicated that the mitochondrial genome may be more variable than once thought. Different gene orders in marsupials and eutherian mammals leave the ancestral mammalian order in some doubt. We have investigated the mitochondrial gene order in the platypus ( Ornithorhynchus anatinus), a representative of the third major group of mammals, to determine which mitochondrial gene arrangement is ancestral in mammals. We have found that the platypus mtDNA conforms to the basic chordate gene arrangement, common to fish, amphibians, and eutherian mammals, indicating that this arrangement was the original mammalian arrangement, and that the unusual rearrangements observed in the avians and marsupials are probably lineage-specific. [ABSTRACT FROM AUTHOR]

The gross anatomy and nerve supply of the bill of echidna ( Tachyglossus aculeatus) is described in relation to its function as an outstanding sensory organ. The sensory innervation of the skin of the echidna snout was investigated by means of frontal serial sections, after decalcification of the specimens. A comprehensive light and electron microscopic description of the location and fine structure of cutaneous sensory receptors of the trigeminal system was made by this means. The encapsulated and non-encapsulated Ruffini receptors, the types of other free receptors in the connective tissue and the Merkel cell receptor do not differ morphologically from those of higher mammals, whereas the pacinian-like corpuscle shows a unique organization of its outer core. This is composed of large perineural cells containing a unique reticulum of parallel-orientated endoplasmic membranes. Lamellated corpuscles, seen in isolation or in association with push rods, are numerous in the snout and in the tip of the tongue of echidna. Push rod receptor organs occur in the hairless skin of the bill with a very dense array at its rostral end and in the pseudopalatal ridges. Gland duct receptors are restricted to the skin adjacent to the nostrils and the mouth opening, including the pseudopalatal plates. Only about one quarter of the total number of 400 seromucous glands receive a sensory innervation of their intraepidermal duct segment. Within each innervated gland two types of receptor terminals are identified. The distributions of the different receptor types are mapped for different regions of the skin, the mucous membrane of the nasal and oral vestibule and the tip of the tongue. The fine structure of nerve terminals is discussed from a comparative anatomical point of view, and some speculations are made about possible transduction processes that underlie the known electrophysiological properties. The sensory organs such as the 'push rod' and 'gland duct receptor', and most of their sensory terminals, are less differentiated in echidna snout than in the platypus ( Ornithorhynchus anatinus) bill. [ABSTRACT FROM AUTHOR]

The dentine and enamel of a newly discovered well-formed tooth of a Tertiary monotreme, Obdurodon sp., was examined for ultrastructural information relevant to the phylogenetic interpretation of monotremes. Obdurodon sp. presents a unique combination of mammalian structural features in the fractured enamel surfaces examined: tubules in great number; prisms of small diameter; a substantial and coherent interprismatic component and, in the middle third enamel, inter-row sheet; a simple non-decussating prism course; a predominantly pattern 1 prism packing in the innermost enamel; and a predominantly pattern 2 prism packing in the middle third enamel; and non-prismatic outer enamel. Although the particular combination of structural characteristics suggests that monotremes represent a possibly unique and relatively plesiomorphic group of mammals, many of the features are very similar to those seen in multituberculates. If multituberculates and monotremes are monophyletic, it would help to explain what has otherwise been a puzzling zoogeographic pattern in the distribution of each group. [ABSTRACT FROM AUTHOR]

Two diploid platypus cell lines, designated Oa-1F and Oa-2F, have been derived from the toe webs of two females. The development and growth characteristics of the lines are described and G-banded karyotypes presented (the first reported for the platypus). The availability of these lines will greatly facilitate chromosome and gene mapping studies of the platypus and permit the extension of comparative studies of mammalian chromosome and genome evolution to the monotremes. [ABSTRACT FROM AUTHOR]