Differential transcriptional activity associated with chromatin configuration in fully grown mouse germinal vesicle oocytes.
It was previously shown that fully grown ovarian germinal vesicle (GV) oocytes of adult mice exhibit several nuclear configurations that differ essentially by the presence or absence of a ring of condensed chromatin around the nucleolus. These configurations have been termed, respectively, SN (surrounded nucleolus) and NSN (nonsurrounded nucleolus). Work from our and other laboratories has revealed ultrastructural and functional differences between these two configurations. The aims of the present study were 1) to analyze the equilibrium between the SN and the NSN population as a function of the age of the mice and the time after hCG-induced ovulation and 2) to study the polymerase I (pol I)- and polymerase II (pol II)-dependent transcription in both types of oocytes through the detection of bromouridine incorporated into nascent RNA. We show 1) that ovarian GV oocytes exhibiting the SN-type configuration can be found as soon as 17 days after birth in the C57/CBA mouse strain and 2) that the SN:NSN ratio of ovarian GV oocytes is very low just after hCG-induced ovulation and then increases progressively with the time after ovulation. Furthermore, we demonstrate that the SN configuration correlates strictly with the arrest of both pol I- and pol II-dependent transcription in mice at any age. Finally, we show that ribosomal genes are located at the outer periphery of the nucleolus in the NSN configuration and that pol I-dependent perinucleolar transcription sites correspond to specific ultrastructural features of the nucleolus. Altogether, these results provide clear-cut criteria delineating transcriptionally active GV oocytes from those that are inactive, and confirm that the SN-type configuration is mostly present in preovulatory oocytes. (+info)
Precocious estrus and reproductive ability induced by PG 600 in prepuberal gilts.
A total of 29 SPF Large White prepuberal gilts (mean age 152 days at treatment) were examined for estrous and ovulatory responses after PG 600 treatment. After treatment, 85.2% of the gilts showed standing estrus within 6 days. Whereas the treatment-to-estrus interval and duration were 3.7 and 1.9 days respectively. As ovulation occurred on Day 5 to 6, appropriate timing of artificial insemination would be about 4 days after treatment. Fertility of gilts revealed to be excellent, giving rise to a high percentage of normal embryos, 85.3%. Meanwhile, development and growth of fetuses were mostly normal. Other reproductive performances recorded were: mean litter size 6.8; mean birth weight 1.26 kg; weaning-to-return estrus interval 5 to 8 days. In conclusion, PG 600 was found to be useful in inducing fertile estrus in prepuberal gilts, a result which will be of interest for commercial pig farms. (+info)
The degenerative fate of germ cells not conforming to stage in the pubertal golden hamster testis.
In the golden hamster (Mesocricetus auratus), pubertal establishment of spermatogenesis includes a defined period (d 26-30 of life) during which elongation of spermatids is selectively arrested. The resulting appearance of germ cell associations not conforming to stage and the phenomenon of desynchronisation-related germ cell degeneration are analysed both quantitatively and qualitatively by means of light and 'retrospective' electron microscopy. From d 26 onwards, the portion of tubules containing non-stage conforming germ cell associations gradually increases up to 37.5% of sectioned tubules on d 32. Concomitantly, the degree of desynchronisation rises to a maturational gap between spermatids and associated younger germ cells of 7 stages of the seminiferous epithelium cycle, i.e. of fully half a cycle. Beyond d 32, the frequency of desynchronised tubule segments decreases again. Some of the arrested round spermatids and, eventually, all belatedly elongating spermatids degenerate and are lost from the epithelium. Thus a regular maturation of advanced spermatids does not succeed under non-stage conforming conditions. Possibly it is not the desynchronisation between the associated germ cell generations and the spermatids by itself that impedes normal further development of the latter cells. Instead this may be due to the maturational delay of the stage-aberrant cells by several stages compared to the seminiferous epithelium as a whole and, especially, in relation to the stage-conditioned functional state of the neighbouring Sertoli cells. (+info)
Leptin and reproduction.
In the few years since leptin was identified as a satiety factor in rodents, it has been implicated in the regulation of various physiological processes. Leptin has been shown to promote sexual maturation in rodent species and a role in reproduction has been investigated at various sites within the hypothalamo-pituitary-gonadal axis. This review considers the evidence that leptin (or alteration in amount of body fat) can affect reproduction. There is evidence that leptin plays a permissive role in the onset of puberty, probably through action on the hypothalamus, where leptin receptors are found in cells that express appetite-regulating peptides. There is little evidence that leptin has a positive effect on the pituitary gonadotrophs and the gonads. There is also very little indication that leptin acts in an acute manner to regulate reproduction in the short term. It seems more likely that leptin is a 'barometer' of body condition that sends signals to the brain. Studies in vitro have shown negative effects on ovarian steroid production and there are no reports of effects on testicular function. Leptin concentrations in plasma increase in women during pregnancy, owing to production by the placenta but the functional significance of this is unknown. A number of factors that affect the production and action of leptin have yet to be studied in detail. (+info)
Effect of long-term food restriction on pituitary sensitivity to cLHRH-I in broiler breeder females.
The effect of long-term food restriction on the sensitivity of the pituitary to exogenously administered chicken luteinizing hormone releasing hormone I (cLHRH-I) was investigated in three groups of broiler breeder females fed ad libitum, fed a restricted quantity of food or fed a restricted quantity of food to obtain an intermediate body weight between those of the first two groups. At 16 weeks of age, basal FSH release was higher in ad libitum fed birds, culminating in ovarian development and subsequent oestradiol production by the small follicles. At this age, LH secretion was independent of ovarian feedback factors. In all groups, cLHRH-I was most active in releasing LH in intact and ovariectomized animals and, to a lesser extent, in releasing FSH in ovariectomized birds. At 39 weeks of age, basal FSH concentrations were similar among intact animals of all groups, whereas LH concentrations differed among groups, with higher values in the restricted birds. This food effect was enhanced in ovariectomized birds. Furthermore, the high response to cLHRH-I in the ovariectomized, restricted birds compared with the ad libitum, ovariectomized group suggests an improved sensitivity of the hypothalamic-pituitary axis. In conclusion, birds fed ad libitum showed the highest responsiveness to ovarian factors and to cLHRH-I in releasing FSH in the period before sexual maturity. No effect of amount of feeding could be observed for LH. However, during the egg laying period, LH release by cLHRH-I was highly dependent on amount of feeding and on ovarian feedback regulation. This finding indicates that the amount of feeding can modify the sensitivity of the pituitary to cLHRH-I, and possibly to gonadal hormones, during the laying period. (+info)
Developmental changes in LH secretion by male pituitaries in vitro: from the infantile to adult period.
The secretion of LH from the anterior pituitary of male rats was studied at different periods of postnatal development. According to an established classification we used rats 14 (infantile), 23 (juvenile), 45 (pubertal) and 90 (adult) days old. By using an in vitro incubation system, both basal and stimulated LH secretion were studied in the same gland. Age-related differences were observed in basal LH secretion, with juvenile and pubertal pituitaries showing higher secretion compared with infantile and adult pituitaries. However, the GnRH-induced secretory response was significantly higher in the infantile rats than in other ages. LH secretion was also studied in primary cultures from infantile or adult pituitaries. In 24 and 48 h cultures, infantile cells showed a significantly larger response to GnRH than that of adult cells. In the infantile pituitary LH-immunopositive cells showed differences in size at different locations in the gland. At the periphery of the lobes the predominant cells were smaller and angular shaped, whereas in the center of the gland the majority of the cells were ovoid shaped. In the adult pituitary, the predominant LH-positive cells were ovoid in shape and larger in size. Furthermore, 10% more LH-positive cells were observed in infantile pituitaries. On the basis of these data we propose that at the infantile period the male rat pituitary has two populations of LH-secreting cells, one with adult secretory function and shape and a second with increased sensitivity to GnRH and with a morphology atypical of the adult cell. The results presented support the hypothesis that the infantile period is a transitional stage in the rat pituitary development. (+info)
Opposing changes in 3alpha-hydroxysteroid dehydrogenase oxidative and reductive activities in rat leydig cells during pubertal development.
The enzyme 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) has an important role in androgen metabolism, catalyzing the interconversion of dihydrotestosterone (DHT) and 5alpha-androstane-3alpha,17beta-diol (3alpha-DIOL). The net direction of this interconversion will affect the amount of biologically active ligand available for androgen receptor binding. We hypothesize that in Leydig cells, differential expression of 3alpha-HSD enzymes favoring one of the two directions is a mechanism by which DHT levels are controlled. In order to characterize 3alpha-HSD in rat Leydig cells, the following properties were analyzed: rates of oxidation (3alpha-DIOL to DHT) and reduction (DHT to 3alpha-DIOL) and preference for the cofactors NADP(H) and NAD(H) (i.e., the oxidized and reduced forms of both pyridine nucleotides) in Leydig cells isolated on Days 21, 35, and 90 postpartum. Levels of 3alpha-HSD protein were measured by immunoblotting using an antibody directed against the liver type of the enzyme. Levels of 3alpha-HSD protein and rates of reduction were highest on Day 21 and lowest on Day 90. The opposite was true for the rate of 3alpha-HSD oxidation, which was barely detectable on Day 21 and highest on Day 90 (59.08 +/- 6.35 pmol/min per 10(6) cells, mean +/- SE). Therefore, the level of 3alpha-HSD protein detectable by liver enzyme was consistent with reduction but not with oxidation. There was a clear partitioning of NADP(H)-dependent activity into the cytosolic fraction of Leydig cells, whereas on Days 35 and 90, Leydig cells also contained a microsomal NAD(H)-activated 3alpha-HSD. We conclude that 1) the cytosolic 3alpha-HSD in Leydig cells on Day 21 behaves as a unidirectional NADPH-dependent reductase; 2) by Day 35, a microsomal NAD(H)-dependent enzyme activity is present and may account for predominance of 3alpha-HSD oxidation over reduction and the resultant high capacity of Leydig cells on Day 90 to synthesize DHT from 3alpha-DIOL. (+info)
Disruption of estrogen signaling does not prevent progesterone action in the estrogen receptor alpha knockout mouse uterus.
Estrogen is known to increase progesterone receptor (PR) levels in the wild-type mouse uterus, and this estrogen induction was thought to be important for progesterone action through the PR. The estrogen receptor alpha knockout (ERKO) mouse uterus was observed to express PR mRNA that cannot be induced by estrogen. Progesterone action was characterized to determine whether it was diminished in ERKO mice. The PR protein is present in the ERKO uterus at 60% of the level measured in a wild-type uterus. The PR-A and PR-B isoforms are both detected on Western blot, and the ratio of isoforms is the same in both genotypes. Although the level of PR is reduced in the ERKO uterus, the receptor level is sufficient to induce genomic responses, since both calcitonin and amphiregulin mRNAs were increased after progesterone treatment. Finally, the ERKO uterus can be induced to undergo a progesterone-dependent decidual response. Surprisingly, the decidual response is estrogen independent in the ERKO, although it remains estrogen dependent in a wild type. These results indicate that estrogen receptor alpha modulation of PR levels is not necessary for expression of the PR or genomic and physiologic responses to progesterone in the ERKO uterus. (+info)