Sertoli cell differentiation in rhesus monkey (Macaca mulatta) is an early event in puberty and precedes attainment of the adult complement of undifferentiated spermatogonia.

In primates, the time course of Sertoli cell proliferation and differentiation during puberty and its relationship with the expansion of undifferentiated type A spermatogonia that occurs at this critical stage of development are poorly defined. Mid and late juvenile and early and late pubertal male rhesus monkeys were studied. Testes were immersion fixed, embedded in paraffin, and sectioned at 5 µm. Sertoli cell number per testis, S-phase labeling (BrdU), and growth fraction (Ki67 labeling) were determined and correlated with corresponding parameters for undifferentiated type A spermatogonia (A dark and A pale). Dual fluorescence labeling was used in addition to histochemistry to monitor spermatogonial differentiation during the peripubertal period using GFRα-1 and cKIT as markers. While the adult complement of Sertoli cells/testis was attained in early pubertal monkeys after only a few weeks of exposure to the elevated gonadotropin secretion characteristic of this developmental stage, the number of undifferentiated type A spermatogonia several months later in mid pubertal monkeys was only 50% of that in adult testes. Both A dark and A pale spermatogonia exhibited high S-phase BrdU labeling at all stages of juvenile and pubertal development. Spermatogonial differentiation, as reflected histochemically and by relative changes in GFRα-1 and cKIT expression, was not observed until after the initiation of puberty. In the rhesus monkey and maybe in other higher primates including human, the pubertal proliferation of undifferentiated spermatogonia is insidious and proceeds in the wake of a surge in Sertoli cell proliferation following termination of the juvenile stage of development.

A re-examination of proliferation and differentiation of type A spermatogonia in the adult rhesus monkey (Macaca mulatta).

BACKGROUND: Companion studies using an experimental non-human primate paradigm known as a testicular clamp indicated that the behavior of undifferentiated type A spermatogonia did not conform fully to earlier classical models. This issue was therefore re-examined in normal monkeys. METHODS: Adult male rhesus monkeys (n = 4) received an i.v. bolus of 5-bromo-2'-deoxyuridine (BrdU): one testis (first) was removed 3 h later and the remaining testis (second) was removed after 11 days and 3 h. Tissue was fixed in Bouin's solution, and numbers of A dark (Ad), small A pale (Aps) and large A pale spermatogonia, differentiating B spermatogonia, S-phase-labeled and degenerating cells were enumerated. Data are given as mean +/- SEM. RESULTS: During the early stages of the seminiferous epithelial cycle in the first testis, Ap spermatogonia (1.3 cells/cross section) were predominantly Aps (nuclear dia., 7.1 +/- 0.1 microm). Aps were never S-phase labeled. Apl (nuclear dia., 8.8 +/- 0.5 microm) appeared in Stages IV-VI and were maximal in Stages VII-X when S-phase labeling of this phenotype at 3 h was greatest. The first generation of B spermatogonia appeared in Stages XI-XII (0.84 cells/cross section). Using cells/cross section, the ratio of Ap (Stages I-V):B1:B2:B3:B4:preleptotene spermatocyte was 1:0.7:1.4:2.8:5.6:11.2. In the second testis, labeled Aps (and Apl) were observed. Ad were not BrdU labeled, and degenerating cells were rarely observed. CONCLUSIONS: The results are not entirely consistent with earlier models of spermatogonial proliferation and differentiation in the monkey. Most notably, our findings suggest that in any one cycle of the seminiferous epithelium only a fraction of Ap spermatogonia is mitotically active.

A selective monotropic elevation of FSH, but not that of LH, amplifies the proliferation and differentiation of spermatogonia in the adult rhesus monkey (Macaca mulatta).

BACKGROUND: Unilateral orchidectomy in monkeys increases spermatogenesis in the remaining testis in association with elevated follicle-stimulating hormone (FSH) secretion and testicular testosterone. The present study examined the relative importance of FSH and testosterone in driving the primate testis toward its spermatogenic ceiling. METHODS: Adult male rhesus monkeys were treated with a gonadotropin-releasing hormone receptor antagonist to inhibit endogenous FSH and luteinizing hormone (LH) secretion. The gonadotrophin drive to the testis was replaced with a pulsatile recombinant human FSH and LH infusion to maintain testicular volume and circulating testosterone and inhibin B at physiological levels. A selective monotropic elevation of FSH or LH that doubled the concentrations of inhibin B or testosterone, respectively, was then imposed for 4 weeks, each in a group of four monkeys. In a third group (n = 4), the gonadotrophin drive remained clamped at physiological levels. Bromo-deoxyuridine was administered 3 h prior to castration, and the effects of the monotropic hormone increments on germ cell number, S-phase labeling and degeneration were determined. RESULTS: Increased FSH, but not LH, produced increases in testicular volume (P < 0.05), the proportion of A pale spermatogonia entering the cell cycle and the numbers of differentiated spermatogonia and more advanced germ cells (P < 0.05). Indexes for spermatogonia labeling and germ cell degeneration were not affected. CONCLUSIONS: Under physiological conditions, circulating concentrations of FSH directly dictate sperm output of the primate testis by regulating the proportion of Ap spermatogonia in the growth fraction. An effect of FSH on survival of the first generation of differentiated B spermatogonia is not excluded.

Impaired germ cell development in the testes of immature rats with neonatal hypothyroidism.

The induction of neonatal hypothyroidism from day 1 to day 25 postpartum using 6-propyl-2-thiouracil (PTU) resulted in a 45% and 77% reduction of testis weight on days 20 and 30, respectively, and an increase in Sertoli cell number. The present study evaluated the effect of neonatal hypothyroidism on the developing germ cell population during the first 30 days postnatally. Qualitative and quantitative studies using the optical disector method were undertaken on the testes of control and hypothyroid rats, on days 10, 20, and 30 after birth. Germ cell development was obviously impaired in the hypothyroid rats, as shown by decreased primary spermatocyte and round spermatid numbers in day 20 and day 30 testes, and the persistence of gonocytes on days 10 and 20. These reductions obviously accounted for the reduced testis weight, absolute volume, and diameter of the seminiferous cords/tubules, especially on days 20 and 30. The failure to establish a seminiferous tubule lumen in hypothyroid rats probably reflects decreased fluid production and a functional immaturity of the Sertoli cells. The delay in germ cell maturation and increased degeneration may be because of the immature state of the Sertoli cell or result from the low follicle-stimulating hormone and thyroxine levels known to occur in the hypothyroid rats.

Increased numbers of Sertoli and germ cells in adult rat testes induced by synergistic action of transient neonatal hypothyroidism and neonatal hemicastration.

The combined effects of transient neonatal hypothyroidism and neonatal hemicastration were investigated to see whether they were additive. Hypothyroidism was induced in litters of ten male rats for 25 days from the day of birth by administration of 0.1% (w/v) 6-propyl-2-thiouracil in the mother's drinking water; hemicastration was performed on the day of birth. Controls included both normal and sham-operated animals. Numbers of Sertoli cells and round spermatids were quantified at age 135 days using stereological methods. Sham-operation had no effect on testis mass, or numbers of Sertoli or germ cells. Transient neonatal hypothyroidism resulted in an increase in testicular mass of 27% (P < 0.05), whereas neonatal hemicastration resulted in a 33% (P < 0.05) increase over control; the combination of the two procedures resulted in a 62% (P < 0.05) increase. There were corresponding significant increases in the number of Sertoli cells: 82% with hypothyroidism, 18% with hemicastration and 123% with the combination of the two procedures. Numbers of round spermatids showed similar increases: 59% with hypothyroidism, 45% with hemicastration and 95% with the combination of the two procedures. It is concluded that the effects of the combination of transient neonatal hypothyroidism and hemicastration are additive with respect to testicular mass, and numbers of Sertoli and germ cells.