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PubMed2001

Sex chromosomes and sex-determining genes: insights from marsupials and monotremes.

Comparative studies of the genes involved in sex determination in the three extant classes of mammals, and other vertebrates, has allowed us to identify genes that are highly conserved in vertebrate sex determination and those that have recently evolved roles in one lineage. Analysis of the conservation and function of candidate sex determining genes in marsupials and monotremes has been crucial to our understanding of their function and positioning in a conserved mammalian sex-determining pathway, as well as their evolution. Here we review comparisons between genes in the sex-determining pathway in different vertebrates, and ask how these comparisons affect our views on the role of each gene in vertebrate sex determination.

Animals↗
PubMed1992

Late postnatal development and differentiation of the ductus epididymidis in a dasyurid marsupial (Antechinus stuartii).

The general histology and ultrastructural features of the developing ductus epididymidis were examined in the brown marsupial mouse, Antechinus stuartii, from April, when males were sexually immature, until August, when the adult males were involved in mating activities, just prior to the annual male die-off. Samples were also examined 3 and 6 months after the August die-off period in males kept in isolation from conspecifics during the prebreeding and breeding periods. In April, tubule diameter and epithelial height were largest in the caput and least in caudal segments but the reverse was observed thereafter. Epithelial height increased in caput segments in August and remained high in the post die-off samples. However, caput epithelial height and tubule diameters were low compared with the remainder of the duct from July until February. Luminal shape in caudal segments (10, 11 and 12) changed in June from circular to a narrow slit, and the epithelium became variable in height. The epididymal epithelium was undifferentiated with few cytoplasmic organelles in April. Differentiation occurred mostly from May to June in association with an increased abundance of cytoplasmic organelles, increasing prostatic weight and rising plasma androgen levels. Differentiated principal and basal cells were found in caput and corpus regions in May and in caudal segments in June in association with the de novo development of a brush border of microvilli. Few clear cells were seen in caput and corpus regions of the duct in May but they, and mitochondria-rich cells, were common throughout the duct from June. Development of the unusual structural features of the cauda epididymidis preceded the arrival of spermatozoa in June. The presence of degenerating spermatozoa and cytoplasmic droplets in the cauda at this time suggested that it was not yet capable of supporting sperm viability. There was no evidence to suggest that the presence of spermatozoa has a stimulatory effect on the epididymis. Intact sperm were observed throughout the duct from July. Free cytoplasmic droplets, which showed some evidence of degeneration, collected in large masses in the distal corpus/proximal cauda epididymidis of adult males between aggregates of spermatozoa. Epididymal differentiation appeared complete by mid-July; few ultrastructural changes occurred after this time. Recruitment of spermatozoa into the epididymis ceased by August and was associated with a rapid decline in sperm content in the proximal caput segments. In the November and February samples, spermatozoa were present only in distal corpus and proximal cauda segments.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

The evolution of protamine P1 genes in dasyurid marsupials.

We report the complete DNA sequences of the protamine P1 gene and flanking regions for 13 species of the marsupial family Dasyuridae. The structure of the protamine locus is conserved in dasyurids and consists of two exons (of lengths 142-151 and 47 bp) separated by an intron (208-240 bp). A key feature of the dasyurid intron is a 38-40 bp duplication found in all species examined to date. This duplication apparently predates the radiation of modern dasyurid lineages and may be homologous to a similar feature in the marsupial mole (Notoryctes). Sequences from a species of Planigale demonstrate that this genus is unique among marsupials in possessing cysteine residues in its protamine P1 molecules. Cysteines may provide enhanced chemical stability for condensed sperm nuclei, a physiological feature that would converge on the common eutherian pattern. Phylogenetic analysis of the protamine genes yields a tree that is largely congruent with previous molecular systematic studies in two areas: (1) There are three main dasyurid lineages corresponding to the Sminthopsinae. Dasyurinae, and Phascogalinae; (2) Dasyurinae and Phascogalinae are sister groups. This study is the first estimate of dasyurid relationships based on a nuclear DNA sequence.

Amino Acid Sequence↗
PubMed1995

Molecular evolution of the mitochondrial 12S rRNA in Ungulata (mammalia).

The complete 12S rRNA gene has been sequenced in 4 Ungulata (hoofed eutherians) and 1 marsupial and compared to 38 available mammalian sequences in order to investigate the molecular evolution of the mitochondrial small-subunit ribosomal RNA molecule. Ungulata were represented by one artiodactyl (the collared peccary, Tayassu tajacu, suborder Suiformes), two perissodactyls (the Grevy's zebra, Equus grevyi, suborder Hippomorpha; the white rhinoceros, Ceratotherium simum, suborder Ceratomorpha), and one hyracoid (the tree hyrax, Dendrohyrax dorsalis). The fifth species was a marsupial, the eastern gray kangaroo (Macropus giganteus). Several transition/transversion biases characterized the pattern of changes between mammalian 12S rRNA molecules. A bias toward transitions was found among 12S rRNA sequences of Ungulata, illustrating the general bias exhibited by ribosomal and protein-encoding genes of the mitochondrial genome. The derivation of a mammalian 12S rRNA secondary structure model from the comparison of 43 eutherian and marsupial sequences evidenced a pronounced bias against transversions in stems. Moreover, transversional compensatory changes were rare events within double-stranded regions of the ribosomal RNA. Evolutionary characteristics of the 12S rRNA were compared with those of the nuclear 18S and 28S rRNAs. From a phylogenetic point of view, transitions, transversions and indels in stems as well as transversional and indels events in loops gave congruent results for comparisons within orders. Some compensatory changes in double-stranded regions and some indels in single-stranded regions also constituted diagnostic events. The 12S rRNA molecule confirmed the monophyly of infraorder Pecora and order Cetacea and demonstrated the monophyly of the suborder Ruminantia was not supported and the branching pattern between Cetacea and the artiodacytyl suborders Ruminantia and Suiformes was not established. The monophyly of the order Perissodactyla was evidenced, but the relationships between Artiodactyla, Cetacea, and Perissodactyla remained unresolved. Nevertheless, we found no support for a Perissodactyla + Hyracoidea clade, neither with distance approach, nor with parsimony reconstruction. The 12S rRNA was useful to solve intraordinal relationships among Ungulata, but it seemed to harbor too few informative positions to decipher the bushlike radiation of some Ungulata orders, an event which has most probably occurred in a short span of time between 55 and 70 MYA.

Animals↗
PubMed1992

Developmental staging in a marsupial Dasyurus hallucatus.

In a marsupial, Dasyurus hallucatus, pouch-young of various ages from newborn to 55 days were embedded in wax and serially sectioned. On the basis of the relative development of external and internal characteristics, they were placed in the Carnegie staging system developed by Streeter and elaborated by O'Rahilly and associates. Birth occurred at stage 15, and the end of embryogenesis (stage 23) was reached about day 33. Whereas stage 23 is characterised in all eutherians by the closure of the secondary palate, this occurs before stage 15 in D. hallucatus. Since most other characters of the newborn are at a stage 15 level of development, there has been a relative acceleration of development of the secondary palate (and forelimb) in D. hallucatus that allows it to suckle and breathe at the same time. Between D. hallucatus and eutherians, there is general agreement in the sequence of development and in the relative degree of most structures at each stage. Further marsupials should be examined to see if the minor differences noted are peculiar to D. hallucatus or apply to marsupials generally.

Animals↗
PubMed1983

Ultrastructure of the reactivated corpus luteum after embryonic diapause in the marsupial, Macropus rufogriseus banksianus.

During embryonic diapause in the red-necked wallaby, M.r. banksianus, both the corpus luteum and uterine blastocyst remain dormant, and are reactivated following removal of the suckling pouch young (RPY). The morphology of dormant and reactivated corpora lutea has been studied throughout the 26.5 days of delayed gestation. Corpora lutea at 0, 2 1/2, 4, 9, 14, 21 and 25 days after RPY were fixed by perfusion. From day 4 to day 14 after RPY there was a progressive increase in the amount of smooth endoplasmic reticulum and the numbers of mitochondria. However there was a decrease in mitochondrial size from 1-2 microns in diameter (0 days after RPY) to 0.5-1 micron (14 days after RPY). Densely-staining granules (approximately 0.2 microns in diameter) were first observed in the luteal cells at 4 days after RPY. The maximum density of granules was observed at 21 days after RPY. Shortly before birth (25 days after RPY) the number of secretory granules had significantly decreased and the features of cellular regression were evident. As with the eutherian mammals, the wallaby luteal cells have all the structural organelles associated with steroid hormone production. The numbers of densely-staining granules are greatest at 21 days after RPY and may reflect the luteal progesterone content since similar granules in the sheep and cow have been shown to be associated with elevated levels of progesterone.

Animals↗
PubMed1982

Ultrastructure of the nongranulated cells and morphology of the extracellular spaces in the pars distalis of adult and pouch-young tammar wallabies (Macropus eugenii).

Differentiated nongranulated (folliculo-stellate) cells were observed in the centre and periphery of the cords of cells in the pars distalis of the adult tammar wallaby (Macropus eugenii). The nongranulated cells formed follicles containing a small lumen: the cell apices were joined by junctional complexes including zonulae adhaerentes and maculae adhaerentes (desmosomes). Follicles of granulated cells were also occasionally found. Follicles were rarely observed in the adult, but were numerous and generally larger in pouch-young wallabies. Moreover, whereas the involvement of granulated cells in the follicles of the adult was infrequent, they were common components of follicular structures in the pouch-young. The marginal cells at the periphery of the pars distalis in contact with the hypophysial cleft had many of the cytological characteristics of the nongranulated cells in the central pars distalis. In both adult and pouch-young wallabies, nongranulated cells at the periphery of the cell cords were juxtaposed such that they formed "sinusoid-like" spaces or lacunae, presumably as part of the extravascular channel system. The observations are discussed in light of the proposed phagocytotic, metabolite and/or hormone transport and "stem cell" roles attributed to these cells.

Aging↗
PubMed1986

Embryo implantation and proteinase activities in a marsupial (Macropus eugenii). Histochemical patterns of proteinases in various gestational stages.

Embryo implantation remains superficial (epithelio-chorial type) in most marsupials including the Macropodidae, but does involve formation of specialized contact zones of the trophoblast with the uterine epithelium. Since in eutherian mammals proteinases appear to play a central role in implantation-initiation mechanisms, a systematic histochemical investigation of proteinase patterns as related to implantation was performed in the tammar wallaby, Macropus eugenii (Macropodidae). Tammar uteri with embryos were collected at diapause and at days 7, 17, 18, 19, 20, 21 and 26 of the 27-day gestational period. Proteinase patterns were studied using a sensitive histochemical gelatin-substrate-film test previously optimized for the detection of trophoblast-dependent proteinase (blastolemmase) in the rabbit. Proteinase patterns were correlated with light-microscopical morphology of the processes of shedding of the extracellular embryo coverings (shell membrane) and attachment of the trophoblast to the uterine epithelium. At acid pH values an intracellular proteinase is detected in yolk sac endoderm and trophoblast as well as in endometrial glands and certain stromal cells. This enzyme is proposed to be a cathepsin indicating high catabolic activity connected particularly with protein transport from the endometrium into the yolk sac. Peak activity is found in the avascular (bilaminar) yolk sac at the phase when contact with the endometrium is being established. A particularly interesting proteinase active at alkaline pH values is detected in the trophoblast-endoderm complex. This enzyme appears to be extruded into the interface between trophoblast and uterine epithelium where it shows maximal activity for only approximately one day, around day (18-)19, exclusively in the bilaminar (avascular) yolk sac. The activity is correlated with the process of shedding of the extracellular embryo coverings (shell membrane) and of subsequent attachment of the trophoblast to the uterine epithelium, in the bilaminar but not the trilaminar (vascular) yolk-sac region. This is the first report on an extracellular (alkaline) proteinase activity possibly serving a specific function in embryo implantation in a marsupial.

Animals↗
PubMed1983

Structure of the pars distalis in pouch-young tammar wallabies (Macropus eugenii).

The pars distalis of pouch-young wallabies (Macropus eugenii) aged 1 to 50 days was studied by means of light-microscopic immunohistochemistry and electron microscopy. In the pars distalis of these pouch-young presumptive somatotrops, which constituted up to 70% of the gland, and nongranulated cells were the most numerous cell types. Small numbers (together representing less than 30% of the pars distalis) of immunoreactive mammotrops, thyrotrops, gonadotrops and corticotrops were also found. The presumptive mammotrops, gonadotrops and thyrotrops increased in number and apparent activity between 1 and 50 days postpartum. Presumptive corticotrop cells in 25 to 30 day-old animals were relatively most numerous, and apparently more active than at any other stage of pouch life; these cells decreased in apparent activity and relative number in older animals. The changes in number and activity of cell types in the pars distalis correlated well with major developmental events such as the onset of adrenal activity, the rapid growth phase in the first 100 days postpartum, and the generally low thyroid activity in pouch-young of less than 50 days of age.

Age Factors↗
PubMed1988

The ultrastructure of the lung of two newborn marsupial species, the northern native cat, Dasyurus hallucatus, and the brushtail possum, Trichosurus vulpecula.

The lungs of newborn northern native cats, Dasyurus hallucatus and newborn brushtail possums, Trichosurus vulpecula were examined by both light and electron microscopy. The native cat has a birth weight of 18 mg after a gestation of about 21 days, whereas the brushtail possum weights 200 mg at birth and has a gestation period of 17.5 days. The lungs of the native cat are two large respiratory sacs, with a respiratory lining of squamous cells and surfactant-secreting cells. The capillaries are located within the connective tissue just below this respiratory epithelium. The visceral covering of the lung is formed by squamous cells. The lungs of the possum are composed of numerous large respiratory sacs which are separated by connective tissue septa in which the capillaries are located. The sacs, as in other species, are lined with squamous cells and surfactant-secreting cells. It is proposed that the structure of the lung of the newborn marsupial is related more to the size of the newborn rather than to the length of the gestation period.

Animals↗
PubMed1984

On the nature of the opaque and translucent enamel regions of some macropodinae (Macropus giganteus, Wallabia bicolor and Peradorcas concinna).

Teeth of three macropod species, M. giganteus, W. bicolor and P. concinna, have been studied using the techniques of light microscopy, scanning- and transmission-electron microscopy and hardness measurement. Light microscope observations showed that the teeth of these species had a translucent enamel region close to the dentine and an outer opaque enamel region at the tooth's surface. These regions were not related to the presence or absence of tubules which are a characteristic feature of marsupial enamel. Hardness tests showed that the opaque enamel was softer than the translucent enamel. Scanning electron microscope observations revealed that there was no correlation between any particular prism packing or orientation and the opaque and translucent enamel regions. Transmission electron microscope observations showed that the translucent enamel region consisted of well defined prisms and well packed, lath-like crystals, whereas the opaque enamel was disrupted by voids (which ranged in size from enlarged micropores to about 2 microns in diameter in extreme cases) between crystals and some randomly oriented, loosely packed crystals. This disruption within the opaque enamel region was more common at prism boundaries but pockets of disrupted enamel were also found within prisms and interprismatic regions. The opacity of the enamel was caused by scattering of light from the voids. The ultrastructure of the opaque enamel region indicated that this region was hypomineralized; hardness tests and polarized light microscope observations were consistent with these results.

Animals↗
PubMed1983

Structure of the pars distalis in the adult tammar wallaby (Macropus eugenii).

An immunohistochemical, light- and electron-microscopial study was made of the pars distalis in adult tammar wallabies (Macropus eugenii). The pars distalis of this marsupial mammal was divided into three regions, based on the distribution of cell types within the gland. Somatotropic, mammotropic, luteotropic, folliculotropic, corticotropic and thyrotropic cells were identified on the basis of their immunohistochemistry, cytology and ultrastructure. Non-granulated (folliculo-stellate) cells, identified in electron micrographs, were found throughout the pars distalis. Somatotropic cells were predominant in the posterior pars distalis in all animals examined. In the single male specimen and in the non-lactating females examined, small numbers of apparently inactive mammotropic cells were scattered throughout the pars distalis; the same cell type was apparently active and present in considerable numbers in lactating females. Only one morphological type of gonadotropic cell was evident; these cells were scattered throughout the pars distalis, but in largest numbers in the median region. Small numbers of thyrotropic cells were found, most commonly in the anterior pars distalis. Corticotrops were also observed in moderate numbers, predominantly in the anterior regions of the pars distalis.

Adrenocorticotropic Hormone↗
PubMed1986

Distribution of glomerular peripolar cells in different mammalian species.

Peripolar cells are granulated glomerular epithelial cells that form a cuff around the vascular pole of the glomerulus. Quantitation of these cells in 17 species of mammals (including man, several laboratory animals and a variety of other species) indicated that they were detectable by light microscopy in all but one of the mammals that were examined (the Australian hopping mouse). In adult mammals with detectable peripolar cells, the "peripolar cell index" (the percentage of randomly sectioned glomeruli that displayed peripolar cells in histological sections of kidney) ranged from 0.15 (for echidna) to 11.86 (for sheep). Newborn lambs and rats showed strikingly high values (23.30 and 10.76, respectively) compared with their adult counterparts. Using electron microscopy, peripolar cells were observed in all species that were examined, including the Australian hopping mouse. Morphologically, peripolar cells were similar in all species although their size and granule population varied. They showed a predominantly outer cortical glomerular distribution and a close anatomical relationship with the renin-containing myo-epithelioid cells. These findings indicate that peripolar cells are present in a wide variety of species and support the view that such cells may play a significant role in the regulation of normal renal function.

Aging↗
PubMed1992

Sex determination and sex reversal: genotype, phenotype, dogma and semantics.

The genetic terminology of sex determination and sex differentiation is examined in relation to its underlying biological basis. On the assumption that the function of the testis is to produce hormones and spermatozoa, the hypothesis of a single Y-chromosomal testis-determining gene with a dominant effect is shown to run counter to the following observed facts: a lowering in testosterone levels and an increase in the incidence of undescended testes, in addition to sterility, in males with multiple X chromosomes; abnormalities of the testes in autosomal trisomies; phenotypic abnormalities of XX males apparently increasing with decreasing amounts of Y-chromosomal material; the occurrence of patients with gonadal dysgenesis and XY males with ambiguous genitalia in the same sibship; the occurrence of identical SRY mutations in patients with gonadal dysgenesis and fertile males in the same pedigree; and the development of XY female and hermaphrodite mice having the same genetic constitution. The role of X inactivation in the production of males, females and hermaphrodites in T(X;16)16H mice has previously been suggested but not unequivocally demonstrated; moreover, X inactivation cannot account for the observed bilateral asymmetry of gonadal differentiation in XY hermaphrodites in humans and mice. There is evidence for a delay in development of the supporting cells in XY mice with ovarian formation. Once testicular differentiation and male hormone secretion have begun, other Y-chromosomal genes are required to maintain spermatogenesis and to complete spermiogenesis, but these genes do not function effectively in the presence of more than one X chromosome. The impairment of spermatogenesis by many other chromosome abnormalities seems to be more severe than that of oogenesis. It is concluded that the notion of a single testis-determining gene being responsible for male sex differentiation lacks biological validity, and that the genotype of a functional, i.e. fertile, male differs from that of a functional female by the presence of multiple Y-chromosomal genes in association with but a single X chromosome. Male sex differentiation in XY individuals can be further impaired by a euploid, but inappropriate, genetic background. The genes involved in testis development may function as growth regulators in the tissues in which they are active.

Animals↗
PubMed1989

Structural features of the epididymis in a dasyurid marsupial (Antechinus stuartii).

The ductus epididymidis of the marsupial mouse Antechinus stuartii was divided into caput, corpus, and caudal regions using several constant morphological landmarks. Tubule diameter and epithelial height increased gradually from caput to cauda. In contrast, the surface area of the lumen of the ductus epididymidis increased to a maximum in the distal caput region, but decreased markedly in the distal cauda in association with characteristic changes in lumen shape (from circular to slit-shaped) and epithelial height. Epithelial cells of the ductus epididymidis were generally similar in structure to those described in other mammalian species. Principal and basal cells were common throughout the epithelium. Clear and mitochondria-rich cells were also identified, but occurred less frequently. Regional variations in cell ultrastructure were observed only in principal cells. Numerous vesicular inclusions occurred in the apical cytoplasm of cells in caput segments, membrane-bounded, electron-dense bodies were common in distal corpus regions, and a brush border of microvilli characterized the luminal surface of principal cells in caudal segments. Sperm index increased in the proximal caput, declined to basal levels in the distal caput and proximal corpus, and then increased to a maximum in segment 9 of the distal corpus and remained at about this level throughout the cauda epididymidis. Nuclear rotation, loss of cytoplasmic droplets, and other sperm maturational changes were observed along the epididymis. Discarded cytoplasmic droplets collected in large masses interspersed between aggregates of spermatozoa throughout the distal regions of the duct. There was no evidence of phagocytosis by principal cells of cytoplasmic droplets. The epididymis of A. stuartii differs from that of other mammals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Cell surface changes during mitosis and cytokinesis of epithelial cells.

PtK2 cells were studied with scanning electron microscopy to record changes on the cell surface during mitosis and cytokinesis. During prophase, prometaphase and metaphase, the cells remain very flat with few microvilli on their surfaces. In anaphase cells, there is a marked increase in the number of microvilli, most of which are clumped over the separating chromosomes and polar regions of the mitotic spindle leaving the surface of the interzonal spindle region relatively smooth. Microvilli appear over the interzonal spindle region in telophase and the cells also increase in height. At the beginning of cleavage, the distribution of microvilli is roughly uniform over the surface but it becomes asymmetric at the completion of cleavage when the daughter cells begin to spread. At this time most microvilli are over the daughter nuclei and the surfaces that border the former cleavage furrow. The regions of the daughter cells distal to the furrow are the first to spread and their surfaces have very few microvilli. When chromosome movement is inhibited by either Nocodazole or Taxol, microvilli formation is inhibited on the arrested cells. Nevertheless cell rounding still takes place in the normal time period. It is concluded from these observations that the signal for the onset of chromosome movement in anaphase is accompanied by a signal for the formation of microvilli. It is suggested that there is also a separate signal for the cell-rounding event in mitosis and that microvilli do not play a role in this contractile process.

Animals↗
PubMed1984

Ultrastructure of the epididymis of the tammar, Macropus eugenii, and its relationship to sperm maturation.

The ductus epididymidis of the tammar is lined by an epithelium composed of principal, mitochondria-rich, apical and basal cells, and intraepithelial leucocytes. The epithelium is structurally differentiated into 6 zones referred to as the initial segment, middle segment (3 subdivisions) and terminal segment (2 subdivisions). The occurrence of the initial, middle and terminal segments corresponds quite closely to the anatomical differentiation of the epididymis into a head, body and tail. The initial segment epithelium in the tammar is lower and has shorter and more slender stereocilia than in other mammals which have been described. Otherwise, the structure of the epithelium has similar characteristics in the tammar to that described in other mammals. Spermatozoa begin to develop the capacity for motility within the initial segment, but only show structural signs of maturation in the middle segment. The sperm head rotates through 90 degrees in the proximal subdivision of the middle segment. The cytoplasmic droplet is detached and spermatozoa develop the capacity for motility in the middle subdivision of the middle segment. The cytoplasmic droplets are phagocytosed by the epididymal epithelium of the middle segment. Sperm storage appears to be the main function of the terminal segment.

Animals↗