Marsupial oocytes are larger and have a thinner zona than eutherian oocytes; and the ooplasm becomes almost completely filled with empty-looking vacuoles the contents of which have, so far, defied histochemical analysis. In the opossum, Monodelphis domestica, apart from orthodox mitochondria, a 'hooded' form is found occasionally in young primary oocytes, and a novel 'spiked' form-which is very elongate and has longitudinally-running filaments attached to the outer membrane--is found in mature oocytes. On the genesis of the ooplasmic vacuoles in mammals, information is available only for two marsupials. In Monodelphis, the vacuoles originate from endoplasmic, endocytotic and Golgi vesicles which generate multivesicular bodies; these give rise to the vacuoles. For the bandicoot, Isoodon macrourus, evidence is presented for the formation of the vacuoles from enlarged, transformed mitochondria which undergo a complex evolution during development. Primordial oocytes of Isoodon contain three ooplasmic localizations--a paranuclear complex, a vesicle microtubule complex and an aggregate of tubular cistenae-which have not been described for other mammalian oocytes. The origin, fate and function of these organelle localizations is unknown. In this paper, problems with respect to the definition of 'yolk' are described and the extent of our ignorance concerning oocyte organelles is discussed.
The first appearance of the mammary and scrotal primordia and the sexual differentiation of the gonads of the brushtail possum, Trichosurus vulpecula, are described. Primordial germ cells were first observed, in fetuses of 7.5 mm crown-rump length, in the gonadal ridges and migrating up the dorsal mesentery. Mammary primordia were first observed in fetuses of 11 mm, and scrotal primordia in those of 12 mm crown-rump length. These structures were diagnostic of female and male brushtail possums respectively. Processus vaginales and gubernacula showed sexual dimorphism, being better developed and appearing earlier in males than in females. Sexual differentiation of the gonads occurred after the appearance of mammary and scrotal primordia, the testes being first recognisable in a 14.5-mm fetus and the ovaries postnatally. Birth occurred between the stages of 14 and 15 mm crown-rump length. These observations appear to indicate that the development of mammary and scrotal primordia are not under gonadal hormonal control, but under direct genetic control, as suggested for the tammar wallaby by previous authors.
This study involved characterization of Leydig cells of the opossum Monodelphis domestica, functionally by immunocytochemical identification of the enzyme 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and by measurement of testosterone levels using RIA. Immunostaining for 3 beta-HSD was first detected in a few Leydig cells on Day 16, was increased by Day 24, reached a peak at 4 mo, and was present even in senescent (3 yr) animals. Plasma testosterone was first measurable (0.35 nM) at prepuberty (3.5 mo). Prior to that, plasma testosterone concentrations were uniformly below the level of detection (< 0.3 nM) in both sexes from Day 5 to 2.5 mo. By 4 mo (puberty), plasma testosterone levels in males had risen significantly to 1.53 +/- 0.35 nM, continuing to increase to 1.79 +/- 0.4 nM at 6 mo and peaking at 2.71 +/- 0.29 nM in the adult (1-2 yr). Ovarian testosterone concentrations were consistently lower than those in the testis, as were those of adrenals of both sexes. Thus the testis would appear to be the major source of androgen production throughout life in this species. Our immunocytochemical study suggests that in Monodelphis, puberty is reached at 4 mo, and this was further supported by a rise in circulating testosterone levels at this time.
(i) Nurse cells and oocytes in the telotrophic ovary of Tenebrio molitor L. (Insecta, Coleoptera-Polyphaga) are differentiated in the larval stadium. (ii) During pupation DNA synthesis occurs in the nurse cells and is probably associated with polyploidy; some of them become multinucleate. The functional significance of these events is interpreted as preparation for subsequent massive RNA synthesis. (iii) The oviducts incorporate [3H]thymidine and undergo elongation due to mitoses. This ceases at eclosion. (iv) RNA synthesis in the pupal ovary is low, but increases in the nurse cells and follicle cells just prior to eclosion. (v) In the adult ovary, once the growth phase has been initiated, a primary oocyte takes about six days to reach maturity. (vi) The nurse cells, though apparently lacking nucleoli, synthesize much stable RNA which reaches each oocyte via a trophic cord. (vii) The follicle cells undergo continuous DNA synthesis: some nuclei contain over 64 times the haploid amount of DNA. Replication is probably asynchronous within a nucleus: this may account for the phenomenon of simultaneous DNA and RNA synthesis in the follicle cells, which also lack nucleoli. (viii) Oogenesis has been divided into nine developmental stages, three of which are vitellogenic. (ix) The oocyte chromosomes are capable of RNA synthesis both when despiralized during early previtellogenesis and after karyosome formation, which occurs at stage 6. (x) The protein content of the oocyte appears to have a dual origin: at least part of the ooplasmic proteins form in situ; while yolk proteins are derived from the haemolymph. The extra-ovarian protein reaches the oocyte via spaces which develop between the follicle cells. (xi) The nucleoplasm becomes more heavily labelled with proteins than the ooplasm. With [3H]leucine, methionine and phenylalanine but not with tryptophane or arginine, there is an increased incorporation into the karyosome. It is suggested that this karyosome-associated protein may function in gene masking. (xii) The significance of these findings is discussed with reference to the literature.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.