Primate spermatogenesis: new insights into comparative testicular organisation, spermatogenic efficiency and endocrine control

Owing to the close phylogenetic relationship of Platyrrhini (New World monkeys) and Catarrhini (Old World monkeys) to man, nonhuman primates are often used as models for the study of male reproductive physiology and endocrinology. This review aims at providing new data and insights into comparative primate spermatogenesis, dealing specifically with quantitative aspects of germinal epithelial organisation and germ cell production, and with the roles of gonadotrophic hormones in this process. Typically, the seminiferous epithelium is composed of specific germ cell associations (spermatogenic stages). In rodents, prosimians and most Catarrhini, tubular cross sections contain a single spermatogenic stage whereas in Platyrrhini, great apes and man multi-stage tubules are present. Since Platyrrhini represent a more basal type of primate, this spermatogenic feature must have developed convergently. The primate multi-stage tubular arrangement was previously believed to be associated with low spermatogenic efficiency. However, recent studies using new methodological approaches and comparing primate species from all taxa have revealed that multistage organisation is compatible with highly efficient spermatogenesis. In fact, meta-analysis demonstrated that the efficiency of spermatogenesis in several nonhuman primate species is comparable to that of rodents which are considered as species with highly efficient germ cell production. The duration of the spermatogenic process was not related to organisation or efficiency of spermatogenesis. Sertoli cell work load was species-specific but had no impact on germ cell numbers and on the efficiency of spermatogenesis. The gonadotrophic hormones, luteinizing hormone (LH) and follicle stimulating hormone (FSH) are the primary regulators of primate testicular function. Recent studies revealed that in New World monkeys chorionic gonadotrophin (CG)--the primate pregnancy hormone--regulates testosterone production instead of LH. Receptor studies demonstrated a dual action of the closely related hormones LH and CG in primates. It is hypothesised that following the divergence of the Platyrrhini lineage from Catarrhini, the LH/CG system evolved independently with ancestral functions of the LH/CG system retained in the neotropical taxa. In summary, key spermatogenic features are preserved across all primate taxa whereas male reproductive endocrinology features appear substantially different in the neotropical primates compared to other primate lineages.     

Role of secreted proteins and gonadotrophins in promoting full maturation of porcine oocytes in vitro

Experiments were designed to identify the extent to which follicle cells and hormones contribute to the developmental competence of porcine oocytes matured in vitro. Oocyte-cumulus complexes were collected from ovaries by dissection and cultured in 2 ml of TCM199-based medium in 5% CO₂ in humidified air at 38.5°C. This basic maturation system was supplemented, for either the first 24 hr only or for the 48-hr culture period, with 1) everted follicle shell alone, 2) gonadotrophic hormones alone, or 3) both follicle shells and hormones. The effect of these treatments was evaluated on 1) meiotic maturation rates, 2) the capacity of matured eggs to undergo activation and early cleavage, and 3) changes to the profile of proteins secreted into the culture medium. The results showed that 1) supplementation with either follicle shell or hormones alone increased the rates of meiotic maturation over the nonsupplemented control group, and 2) combined follicle shell and hormonal supplementation yielded the highest rates for maturation, activation, and cleavage but only when hormonal supplementation was removed after the first 24 hr of culture. Proteins of 30, 37, 45, and 46 kD, but of unknown function, were secreted during the first 24 hr into the culture medium in groups supplemented with follicle shells. The addition of hormones did not affect this pattern of secreted proteins. It is possible that some secreted proteins may act to facilitate full maturation of pig oocytes. Mol. Reprod. Dev. 47:191–199, 1997. © 1997 Wiley-Liss, Inc.     

Follicle stimulating hormone and luteinizing hormone levels in buffalo seminal plasma

The levels of follicle stimulating hormone (FSH) and luteinizing hormone (LH) were determined in the buffalo bull seminal plasma by double-antibody radioimmunoassay. The mean levels of FSH and LH ranged from 8.98 ± 3.08 to 18.40 ± 2.19 ng/ml and from 0.598 ± 0.200 to 1.22 ± 0.334 ng/ml, respectively. FSH and LH concentration was positively correlated with mass motility and sperm concentration of buffalo semen samples. Concentration of hormones did not differ significantly among bulls.     

Effects of gonadotrophins, growth hormone, and activin A on enzymatically isolated follicle growth, oocyte chromatin organization, and steroid secretion

So far, standard follicle culture systems can produce blastocyst from less than 40% of the in vitro matured oocytes compared to over 70% in the in vivo counterpart. Because the capacity for embryonic development is strictly associated with the terminal stage of oocyte growth, the nuclear maturity status of the in vitro grown oocyte was the subject of this study. Mouse early preantral follicles (100-130 microm) and early antral follicles (170-200 microm) isolated enzymatically were cultured for 12 and 4 days, respectively, in a collagen-free dish. The serum-based media were supplemented with either 100 mIU/ml FSH (FSH only); 100 mIU/ml FSH + 10 mIU/ml LH (FSH-LH); 100 mIU/ml FSH + 1 mIU/ml GH (FSH-GH) or 100 mIU/ml FSH + 100 ng/ml activin A (FSH-AA). Follicle survival was highest in follicle stimulating hormone (FSH)-AA group in both cultured preantral (91.8%) and antral follicles (82.7%). Survival rates in the other groups ranged between 48% (FSH only, preantral follicle culture) and 78.7% (FSH only, antral follicle culture). Estradiol and progesterone were undetectable in medium lacking gonadotrophins while AA supplementation in synergy with FSH caused increased estradiol secretion and a simultaneously lowered progesterone secretion. Chromatin configuration of oocytes from surviving follicles at the end of culture revealed that there were twice more developmentally incompetent non-surrounded nucleolus (NSN) oocytes (>65%) than the competent surrounded nucleolus (SN) oocytes (<34%). We conclude that the present standard follicle culture system does not produce optimum proportion of developmentally competent oocytes.