Biomedical subjects

G F Weinbauer

Publications and source records attributed to G F Weinbauer.

113 records · Page 7Linked to original sources

PubMedDate not supplied

Round spermatids show normal testis-specific H1t but reduced cAMP-responsive element modulator and transition protein 1 expression in men with round-spermatid maturation arrest.

During spermiogenesis, histones are replaced by transition proteins, which in turn are replaced by protamines. The TNP1 gene-encoding TP1 (transition protein 1) protein contains a cAMP-responsive element (CRE) that serves as binding site for the CRE modulator (CREM). To gain further insight into the complex regulation of nucleoprotein exchanges in haploid spermatids and its potential role for spermatogenic impairment, we studied the gene expression of testis-specific histone H1t, CREM, and TNP1 in testicular biopsies from men with normal spermatogenesis (n = 20) and with round spermatid maturation arrest (n = 16). During normal spermatogenesis, H1t messenger RNA (mRNA) was present in 86.2%+/-8.7% of pachytene spermatocytes (stages III-V), whereas H1t protein was synthesized in 83.5%+/-13.0% of pachytene spermatocytes (stages III-V) and persisted in 95.2%+/-3.1% of spermatids (steps 1-5). CREM mRNA was detectable in 74.2%+/-9.4% of pachytene spermatocytes (stages IV-V) and in 78.7%+/-10.0% of spermatids (steps 1-3). CREM protein was synthesized in 81.2%+/-14.2% of spermatids (steps 1-3). TNP1 mRNA was present in 80.0%+/-13.5% of spermatids (steps 2-4), whereas TP1 protein was synthesized in 89.7%+/-5.3% of spermatids (steps 3-4). In men with round spermatid maturation arrest, spermatids only develop to step 3 of differentiation. These spermatids were devoid of both CREM and TP1 but did contain H1t. These results indicate that TP1 is likely to be an important parameter in the histone-to-protamine exchange and in the initiation of spermatid elongation. CREM is involved in the regulation of TNP1 gene expression and consequently plays a vital role in the correct differentiation step from round spermatids to mature spermatozoa.

Chromosomal Proteins, Non-Histone↗

PubMedDate not supplied

The duration of the cycle of the seminiferous epithelium is altered by administration of 2,5-hexanedione in the adult Sprague-Dawley rat.

The duration of the cycle of the seminiferous epithelium is believed to be under genetic control rather than being influenced by other factors. However, the frequencies of certain spermatogenic stages--reflecting their relative durations--can be altered under various conditions including treatment with the n-hexane metabolite, 2,5-hexanedione (HD). To investigate whether HD administration alters the duration of the spermatogenic process, adult Sprague-Dawley rats were exposed to vehicle (n = 20) or 1% HD dissolved in the drinking water (n = 40) throughout a period of 29 days. On day 17, 100 mg/kg of 5-bromodeoxyuridine (BrdU) was given intraperitoneally; 3 hours later one testis was removed, and the remaining testis was excised 12 days later. BrdU was localized in Bouin's-fixed, Paraplast-embedded testes using immunogold-silver-staining, and sections were counterstained with periodic acid--Schiff and hematoxylin to permit identification of the spermatogenic stages. HD treatment reduced weights of body, testis, and epididymis (P < 0.05) but had no effects on serum levels of follicle-stimulating hormone or testosterone. The seminiferous epithelium was vacuolized, and spermatogenesis was affected to various degrees. HD significantly reduced the frequency of stage VII tubules (P < 0.01) and increased the frequency of stage IX and stage X tubules (P < 0.05). Furthermore, HD reduced the stage-dependent progression of BrdU-labeled germ cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

Appearance of alpha-smooth muscle actin in peritubular cells of monkey testes is induced by androgens, modulated by follicle-stimulating hormone, and maintained after hormonal withdrawal.

This study analyzed the hormonal requirements necessary for the development of primate testicular peritubular cells. Alpha-smooth muscle actin, as a specific differentiation marker for peritubular cells, was immunohistochemically detected in the testes of immature rhesus and adult rhesus and cynomolgus monkeys. Positive staining was localized in the wall of blood vessels and in peritubular myoid cells of adult animals. In the testis of vehicle-treated immature monkeys no positive staining could be detected in peritubular cells. Following follicle-stimulating hormone (FSH) or testosterone treatment, immunostaining for alpha-smooth muscle actin appeared in peritubular cells of immature animals. In comparison to FSH, testosterone was more effective in inducing the differentiation of peritubular cells. The most intense label for alpha-smooth muscle actin was, however, obtained after combined treatment with FSH and testosterone. A computer-assisted image analysis system was used to evaluate semiquantitative data for the alpha-smooth muscle actin positive area; this confirmed a significantly higher expression of alpha-smooth muscle actin in peritubular cells of immature monkeys after treatment with testosterone plus FSH in comparison to controls. These data present evidence that the differentiation of primate peritubular cells during pubertal sexual development is a hormone-dependent process, which may be predominantly regulated by androgens. FSH exerted additive effects on the androgen-induced differentiation of peritubular cells, suggesting that paracrine communication between peritubular cells and Sertoli cells existed. Maintenance of peritubular cell differentiation after withdrawal of hormonal stimuli in adult monkeys may be a possible explanation for different hormonal requirements during reinitiation of spermatogenesis after testicular involution.

Actins↗

PubMedDate not supplied

Maturation of monkey spermatozoa in the epididymis with respect to their ability to undergo the acrosome reaction.

Spermatozoa obtained along the length of the epididymides from five macaque monkeys (Macaca fascicularis) were examined for their ability to undergo the acrosome reaction under basal conditions and when stimulated with the calcium ionophore A23187. Under basal conditions (2.5 hours incubation in potentially capacitating medium) few epididymal sperm cells displayed the loss of acrosome as judged by staining with peanut agglutinin lectin that binds to the outer acrosomal membrane, regardless of the epididymal region from which they were retrieved. By contrast, there was a marked difference in response to short (0.5 hour) incubation with the calcium ionophore A23187, which induced acrosome reactions in the majority of caudal sperm: caput sperm failed to respond at all and corpus sperm were about 50% as responsive as caudal spermatozoa. There is thus a development of the ability to respond to the ionophore upon maturation. Ejaculated spermatozoa from the same monkeys displayed a higher rate of basal acrosomal loss but a slightly lower stimulated response than mature epididymal spermatozoa. With these maturational aspects, monkey epididymal sperm can serve as a model for the study of human sperm maturation.

Acrosome↗

PubMedDate not supplied

Quantification of apoptotic testicular germ cells in normal and methoxyacetic acid-treated mice as determined by flow cytometry.

Several studies have reported the occurrence and significance of programmed cell death (apoptosis) of testicular germ cells in mammals. In those studies, apoptotic germ cells were identified by morphological criteria or by in situ end labeling (TUNEL) and were enumerated from histological sections by semi-quantitative and time-consuming techniques. In the present study, we have established a flow cytometric technique for quantification of TUNEL-positive cells in the mouse testis. Groups of five adult mice each received 0, 650, or 1300 mg/kg (IP) of methoxyacetic acid (MAA), and testes were collected 24 hours later. MAA is known to induce germ cell apoptosis in rodent testes. MAA induced a significant (P < 0.01) dose-dependent decline in the percentage of pachytene spermatocytes (4C cells). DNA strand breaks generated by the activation of endogenous endonuclease in the apoptotic germ cells were detected by the in situ labeling of the 3'-OH termini with biotinylated dUTP in the presence of terminal deoxynucleotidyl transferase (TUNEL technique). Histologically, TUNEL-positive germ cells were observed in control testes, and the number of these cells was visibly increased following MAA exposure. As determined by flow cytometry, four cell populations contained TUNEL-positive cells: 1C cells (round spermatids), 2C cells (mainly spermatogonia), S-ph cells (spermatogonial cells and preleptotene spermatocytes synthesizing DNA [the S-phase]), and 4C cells (primary spermatocytes). Analysis of the percentages of TUNEL-positive cells within each population yielded values of 1.57+/-0.23% for 1C cells, 1.65+/-0.27% for 2C cells, 6.26+/-1.03% for S-ph cells, and 3.24+/-0.39% for 4C cells. Hence, a substantial proportion of proliferating cells are undergoing apoptosis during normal spermatogenesis. The overall incidence of apoptotic cells among all testicular cells was around 2%. At 650 mg per kilogram of body weight, MAA induced a fourfold to eightfold increase (P < 0.001) in the percentage of TUNEL-positive cells, compared with saline-treated controls, and, overall, 17% of testicular cells were apoptotic. This effect of MAA was most pronounced for S-ph and 4C cells, with 25-30% of cells being affected in each of those populations. At 1300 mg per kilogram of body weight, MAA had no further effect. These quantitative data demonstrate that 1) in the normal testis, it is mainly proliferating cells that undergo apoptosis, and 2) MAA induces primary spermatocyte loss by germ cell apoptosis.

Acetates↗