Postnatal induction of ovogenesis in the rabbit (Oryctolagus cuniculus)

Primordial follicle activation and follicular development in the juvenile rabbit ovary

Of all the stages of mammalian folliculogenesis, the primordial to primary follicle transition is the least understood. In order to gain new insights into this process, we have conducted a comprehensive morphological, morphometric and molecular study of ovarian organisation and early follicle development in the rabbit. The structure of ovaries collected from rabbits aged from 2-12 weeks (a period encompassing primordial follicle formation, activation and the first wave of folliculogenesis in this species) has been analysed by light microscopy and the follicles present have been measured and scored for their developmental stage. To establish useful molecular markers of activation, we have further classified follicles according to their expression of the proliferative marker, proliferating cell nuclear antigen, and the zona pellucida protein, ZPB. The activation of primordial follicles is initiated immediately following their formation in the rabbit ovary and is characterised by oocyte growth, granulosa cell morphogenesis and increased granulosa cell mitosis. Enhanced ZPB protein expression at the oolemma is also associated with follicle activation and development. Few primordial follicles in the juvenile rabbit ovary are lost by atresia, as assessed by the TUNEL assay. The appearance of apoptotic granulosa cells is however coincident with the development of antral follicles. This study thus describes the temporal and spatial regulation of early follicular development in the post-natal rabbit ovary and, for the first time, shows that the primordial to primary transition in the juvenile rabbit is a highly ordered process occurring within quantifiable parameters.

Expression of RUSH transcription factors in developing and adult rabbit gonads

The RUSH transcription factors 1alpha and 1beta bind to the Rabbit Uteroglobin promoter and are members of the SWI/SNF complex that facilitates transcription by remodeling chromatin (Helicase). To characterize gonadal expression of RUSH, a cRNA probe that recognizes both isoforms was used for in situ hybridization studies. We found RUSH mRNA to be abundant in Sertoli cells from embryonic, neonatal, prepubertal, and pubertal rabbit testes. In adults, RUSH mRNA was detected in tubules with preleptotene spermatocytes and mature spermatids lining the lumen. However, RUSH was undetectable in tubules that contained leptotene spermatocytes and that lacked mature spermatids. In females, RUSH was expressed in presumptive granulosa cells of embryonic and neonatal ovaries before follicle organization. Abundant RUSH mRNA was detected in granulosa and theca cells surrounding preantral follicles of prepubertal and adult ovaries. Expression of RUSH remained high in granulosa cells of antral follicles in mature ovaries but was negligible in late-stage atretic follicles and in corpora lutea. Western blot analysis confirmed the RUSH-1alpha isoform predominated in both testicular and ovarian tissues. The expression pattern of RUSH indicates transcriptional activity in Sertoli cells and during multiple stages of differentiating granulosa cells, especially those of primordial follicles, which heretofore were considered to be dormant.

Oogenesis in lorises; Loris tardigradus lydekkerianus and Nycticebus coucang

A histological study of ovaries in three pairs of foetal and 67 pairs of postnatal slender lorises of different age groups ranging from suckling young to adults was made. Oogonia in interphase and mitosis, as well as non-follicular germ cells in various stages of meiotic prophase, were present in all the ovaries. Similar germ cells were also found in 12 pairs of postnatal slow loris ovaries. Aquantitative estimation of the primordial germ cell population was also made in the 67 pairs of postnatal slender loris ovaries. The total number of germ cells decreases with age from the time of birth until puberty. In the adults the primordial germ cell population varies in relation to the different phases of the reproductive cycle. This suggests that oogenesis in postnatal lorises may be under endocrine control. The number of germ cells increases progressively during pro-oestrus and oestrus and reaches a peak of ca . 171 000 cells during early pregnancy. Thereafter the number declines to a level of about 20 000 during lactation and drops to a level of ca . 10 000 during anoestrus. The fate of all the freshly formed germ cells during each oestrous cycle is not known. It is likely that most of them perish since the number of atretic cells is also high during phases of increased oogenetic activity. It remains to be shown whether any of the newly formed cells contribute to the definitive germ cell population.

Changes in 3 beta-hydroxysteroid dehydrogenase activity in the developing rabbit ovary

The presence of 3 beta-hydroxysteroid dehydrogenase in the maturing rabbit ovary was demonstrated biochemically and histochemically. Enzyme activity was negligible to absent in ovaries from rabbits less than 44 days old. The greatest activity was located in the microsomal fraction of ovaries from mature rabbits. The enzyme characteristics were: Vmax = 33.1 +/- 9.6 nmol/min/mg protein and Km = 2.16 +/- 0.28 microM. Ovaries from pregnant hyperglycemic rabbits had enzyme which showed a Vmax of 51.4 +/- 8.2 nmol/min/mg protein and Km = 2.41 +/- 0.31 microM. These results indicate that rabbit ovarian tissue becomes steroidogenically active at a time when gonadotropin levels are elevated.

Morphologically distinctive X chromosome in the female chromosome complement of the rabbit

Further evidence is provided to support the classification of the X chromosome of the domestic rabbit as one which is medium-sized with a sub-metacentric centromere. In female metaphase plates, one X chromosome may be easily identified by its striking heteropycnosis, smoothness of outline, thinner chromatid arms in relation to others in the complement, and peripheral or near-peripheral location. Occasionally a kink is seen midway along its long arm.

Dictyotene Stage of Meiosis in Mosses

The dictyotene stage of first meiotic prophase, characterized by an elongation of the paired chromosomes after diplotene, and known to occur during the growth period of the oocytes of many animals, has a morphologically analogous but relatively short-lived counterpart in the first meiotic prophase of representatives from three moss families.