The normal fine structure of opossum testicular interstitial cells.
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The interstitial tissue of the opossum testis includes interstitial or Leydig cells, macrophages, and small cells which morphologically resemble mesenchymal cells. The latter are thought to give rise to mature interstitial cells. The most prominent feature of the interstitial cell cytoplasm is an exceedingly abundant agranular endoplasmic reticulum. This reticulum is generally in the form of a meshwork of interconnected tubules about 300 to 450 A in diameter, but occasionally it assumes the form of flattened, fenestrated cisternae resembling those of pancreatic acinar cells, except for the lack of ribonucleoprotein particles on the surface of the membranes. The interstitial cells vary considerably in their cytoplasmic density. The majority are quite light, but some appear extremely dense, and in addition usually have a more irregular cell surface, with numerous small pseudopodia. These differences may well reflect variations in physiological state. Cytoplasmic structures previously interpreted as "crystalloids" consist of long bundles of minute parallel tubules, each about 180 A in diameter, which seem to be local differentiations of the endoplasmic reticulum. The mitochondria are rod-shaped, and contain a moderately complex internal membrane structure, and also occasional large inclusions that are spherical and homogeneous. The prominent juxtanuclear Golgi complex contains closely packed flattened sacs and small vesicles. The results of the present study, coupled with biochemical evidence from other laboratories, make it seem highly probable that the agranular endoplasmic reticulum is involved in the synthesis of the steroid hormones produced by the interstitial cell. This finding therefore constitutes one of the first functions of the agranular reticulum for which there is good morphological and biochemical evidence. (+info)
Hair follicle differentiation: expression, structure and evolutionary conservation of the hair type II keratin intermediate filament gene family.
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During hair follicle development several cell streams are programmed to differentiate from the cell population of the follicle bulb. In the hair cells, a number of keratin gene families are transcriptionally activated. We describe the characterization of the type II keratin intermediate filament (IF) gene family which is expressed early in follicle differentiation. In sheep wool, four type II IF proteins are expressed. One gene has been completely sequenced and the expression of three of the genes examined in detail. The sequenced gene encodes a 55 x 10(3) Mr protein of the type II keratin IF protein family, designated KII-9 in the new nomenclature we have adopted and described in the Introduction. The gene has a similar exon/intron structure to the epidermal type II keratin IF genes. In situ hybridization experiments show that the genes are expressed in the hair cortical cells but not in the cells of the outer root sheath, inner root sheath or medulla. During hair keratinocyte differentiation the type II IF genes are sequentially activated and coexpressed in the same cells. Expression is first detected in cells in the middle of the follicle bulb located near the dermal papilla and, subsequently, two of the genes are transcriptionally activated in the differentiating keratinocytes as they migrate upwards, in the upper part of the bulb. A fourth type II IF gene is activated later. The genes with the same expression pattern are also closely related in sequence and a number of conserved elements are present in the promoters of those genes, including a novel element which is also found in the promoter of a coexpressed type I IF gene and three other hair keratin genes. (+info)
Steroid hormone content of the gonads of the tammar wallaby during sexual differentiation.
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The gonads of the tammar wallaby, Macropus eugenii, are sexually indifferent at birth (Day 0) despite the fact that phenotypic sexual differentiation has already commenced as evidenced by the presence of a scrotum in males and mammary anlagen in females. The seminiferous cords of the testis first become clearly recognizable on Day 2 of pouch life, and ovarian differentiation is recognizable by Day 10. To monitor the endocrine development of the gonads during sexual differentiation of the urogenital tract, we measured the steroid hormone content in 92 pools of gonads from male and female tammar pouch young from the day of birth to 206 days of pouch life. Progesterone, estradiol, and dihydrotestosterone concentrations were low (less than 0.05 ng/mg protein) in both ovaries and testes at all stages examined, and testosterone concentrations were uniformly low in ovaries. Testosterone concentrations in testes were low on Days 0-4, averaging about 0.2 ng/mg protein; they rose by Days 5-10 to an average of 0.9 ng/mg protein, remained elevated until about Day 40, and thereafter fell to values similar to those in the ovaries. The phallus and urogenital sinus were able to convert testosterone to dihydrotestosterone from the earliest stages examined (Days 10 and 11). Thus in the tammar wallaby, as in eutherian mammals, testosterone is the androgen secreted by the developing testis, and dihydrotestosterone is formed in certain androgen target tissues.(ABSTRACT TRUNCATED AT 250 WORDS) (+info)
The role of photoperiod on the initiation of the breeding season of the brushtail possum (Trichosurus vulpecula).
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The role of photoperiod on the initiation of the breeding season of brushtail possums was investigated in possums housed in three light regimens: a short-day, a natural and a long-day photoperiod. Seven possums were housed in a natural photoperiod. Four possums were transferred to a short-day photoperiod (10 h light, 14 h dark) and eight possums to a long-day photoperiod (14 h light, 10 h dark) on 22 November, when the daylength was 13.34 h. The first rises in plasma progesterone concentrations were observed on 9 January +/- 9 days (n = 4), 11 March +/- 6 days (n = 7) and 6 May +/- 6 days (n = 8), for possums held in short-day, natural or long-day photoperiods respectively. Similarly, births were observed on 12 January and 14 February in the short-day group, from 3 March to 8 May for the natural photoperiod group, and from 5 May to 8 August for the long-day group. These results suggest that photoperiod is important in the timing of the breeding season. However, annual breeding will commence in a nonstimulatory long-day photoperiod. Thus a long-day photoperiod does not prevent breeding activity. (+info)
Evidence that cortical granule formation is a periovulatory event in marsupials.
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Formation of cortical granules was examined in superovulated oocytes from three marsupial species, brushtail possums (Trichosurus vulpecula) tammar wallabies (Macropus eugeniii) and grey short-tailed opossums (Monodelphis domestica) and in oocytes obtained during natural cycles in Macropus eugenii. Superovulation was induced by pregnant mares' serum gonadotrophin/gonadotrophin-releasing hormone (PMSG/GnRH) protocols and natural ovulation by removal of pouch young. Oocytes were collected after ovariectomy or by laparoscopically guided follicle aspiration into Hanks balanced salt solution (HBSS) supplemented with either 2.5% fetal calf serum (FCS) or 2.5% bovine serum albumin (BSA). Ovulated oocytes were collected by removing and flushing the oviducts with HBSS and fixed immediately for electron microscopy. There were no differences in the morphology or timing of formation of cortical granules between superovulated and naturally cycling animals. Cortical granules were absent from germinal vesicle (GV) stage follicular oocytes before the luteinizing hormone (LH) surge in all species. Dark cortical granules, similar in appearance to those seen in the oocytes of eutherian mammals, were found just beneath the plasma membrane (9 per 100 microns of plasma membrane) of preovulatory oocytes at germinal vesicle, metaphase 1 or anaphase 1 stages. In addition, they contained a number of less electron-dense cortical granules (12 per 100 microns plasma membrane). The cortical cytoplasm of preovulatory oocytes was rich in Golgi complexes actively involved in vesicle formation. Large numbers of dark cortical granules (90 per 100 microns plasma membrane) were found only in ovulated oocytes. A small number of cortical granules of lighter electron density were also present in ovulated oocytes. This suggests that the marsupial oocyte is following a very different timetable for cortical granule formation and accumulation from eutherian mammals and that oocytes of marsupials may not achieve cytoplasmic maturity until after ovulation. The significance of these events for fertilization and development remains to be established. (+info)
EFFECT OF ENVIRONMENTAL TEMPERATURES ON INFECTION WITH MYCOBACTERIUM MARINUM (BALNEI) OF MICE AND A NUMBER OF POIKILOTHERMIC SPECIES.
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Clark, H Fred (Communicable Disease Center, Atlanta, Ga.), and Charles C. Shepard. Effect of environmental temperatures on infection with Mycobacterium marinum (Balnei) of mice and a number of poikilothermic species. J. Bacteriol. 86:1057-1069. 1963.-An exploration was made of the effect of environmental temperature on infections with Mycobacterium marinum of mice, young opossums, and bats, and of 50 species of poikilothermic animals. In artificial medium (7H9 broth) M. marinum grew most rapidly from 25 to 35 C, with generation times of 4 to 6 hr. At 37 C, the generation time was 14 hr; at 20 C, 20 hr; and, at 15 C and lower, little growth was observed. In mice, deep body temperatures were found to be 36.5 to 37.3 C at environmental temperatures of 4 to 30 C. At an environmental temperature of 34 C, they averaged 39.1 C; at 37 C they averaged 40.2 C. Foot-pad temperatures were within a few degrees of ambient temperatures from 10 to 34 C. In mouse foot-pad infections, the optimal environmental temperature for infection was 20 C, and the generation time of the infecting bacilli at this environmental temperature was about 15 hr. Intravenously inoculated mice developed peripheral infections of nose, feet, and tail at environmental temperatures of 4 to 30 C. At these temperatures, they had severe pneumonic involvement, and the mice at lower temperatures tended to succumb most rapidly to systemic infection. At 34 C, the intravenously infected mice did not develop peripheral infections and there was no pulmonary involvement. Young opossums, whose deep body temperatures are only 34 to 36 C, were inoculated in the foot-pad and intravenously. Foot-pad infection developed without systemic involvement. Bats, which assume environmental temperature when at rest, were inoculated in the foot-pad. Foot-pad infections were observed but no systemic disease. The bats could be maintained for only short periods, however. Poikilothermic animals were studied. Deep body temperatures were found to be nearly identical with ambient temperature. A total of 50 species of reptiles, amphibians, and fish were infected intraperitoneally in a number of experiments, as animals were available. Susceptibility to M. marinum was found throughout these species. There was no tendency to peripheral involvement. In experiments to determine the optimal environmental temperature for infection, cricket frogs (Acris), American chameleons (Anolis), young garter snakes (Thamnophis), and the young of three species of turtles were inoculated intraperitoneally. The optimal temperature for infection was found to be 30 C in each case, and infections at 20 C were definitely slower. The generation time of M. marinum in American chameleons at 30 C was about 19 hr; at 20 C, it was about 46 hr; and, at 10 C, the bacilli did not apparently multiply. Transmission studies revealed instances where infected animals shed M. marinum into the waters in which they were kept, and where animals became infected from water containing M. marinum. (+info)
FINE STRUCTURE OF THE NEUROHYPOPHYSIS OF THE OPOSSUM (DIDELPHIS VIRGINIANA).
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The neurohypophysis of the opossum (Didelphis virginiana) was studied by electron microscopy in order to amplify Bodian's classic light microscopic observations in which he demonstrated a definite lobular pattern. The lobule of the opossum neurohypophysis is divided into three regions: a hilar, a palisade, and a septal zone. The hilar portion contains bundles of nerve fibers, the extensions of the hypothalamo-hypophyseal tract containing neurofilaments but few neurosecretory granules. In the opossum, pituicytes have a densely fibrillar cytoplasm. Herring bodies are prominent in the hilar region. They are large bodies packed with neurosecretory granules that have been described as end bulb formations of axons. From the hilar region, axons fan out into a palisade zone where the nerve terminals packed with neurosecretory granules, mitochondria, and microvesicles abut upon basement membranes. The neurosecretory granules are similar to those present in the neurohypophysis of other mammals, except for an occasional huge granule of distinctive type. Material morphologically and histochemically resembling glycogen occurs as scattered particles and as aggregates within nerve fibers. The septal zone, containing collagen, fibroblasts, and numerous small capillaries, is separated from the adjacent glandular tissue by a basement membrane. (+info)
Does female mortality drive male semelparity in dasyurid marsupials?
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In some members of the marsupial families Didelphidae and Dasyuridae, males are semelparous, that is, they live for only one mating season. Semelparity is proposed to be the result of the high energy demands of competing for matings with many females during a short breeding season. We argue that high adult female mortality rates between mating and weaning of the offspring selects for a 'bethedging' mating strategy in males. We tested this hypothesis in a well-studied field population of Antechinus agilis by estimating the number of females a male needs to mate with in order to have a high chance of siring at least one offspring that survives to the next breeding season. Our hypothesis predicts that species in which males are semelparous should have higher female mortality rates than species in which males are iteroparous. The limited available data for dasyurid marsupials support this prediction. (+info)