Differentiation of the rat testis between 20 and 120 days of age

Emerging connectivity of programmed cell death pathways and its physiological implications

The removal of functionally dispensable, infected or potentially neoplastic cells is driven by programmed cell death (PCD) pathways, highlighting their important roles in homeostasis, host defence against pathogens, cancer and a range of other pathologies. Several types of PCD pathways have been described, including apoptosis, necroptosis and pyroptosis; they employ distinct molecular and cellular processes and differ in their outcomes, such as the capacity to trigger inflammatory responses. Recent genetic and biochemical studies have revealed remarkable flexibility in the use of these PCD pathways and indicate a considerable degree of plasticity in their molecular regulation; for example, despite having a primary role in inducing pyroptosis, inflammatory caspases can also induce apoptosis, and conversely, apoptotic stimuli can trigger pyroptosis. Intriguingly, this flexibility is most pronounced in cellular responses to infection, while apoptosis is the dominant cell death process through which organisms prevent the development of cancer. In this Review, we summarize the mechanisms of the different types of PCD and describe the physiological and pathological processes that engage crosstalk between these pathways, focusing on infections and cancer. We discuss the intriguing notion that the different types of PCD could be seen as a single, coordinated cell death system, in which the individual pathways are highly interconnected and can flexibly compensate for one another.

Sertoli cells are capable of proliferation into adulthood in the transition region between the seminiferous tubules and the rete testis in Wistar rats

Sertoli cells (SCs) play a crucial role in testis differentiation, development and function, determining the magnitude of sperm production in sexually mature animals. For over 40 years, it has been considered that these key testis somatic cells stop dividing during early pre-pubertal phase, between around 10 to 20 days after birth respectively in mice and rats, being after that under physiological conditions a stable and terminally differentiated population. However, evidences from the literature are challenging this dogma. In the present study, using several important functional markers (Ki-67, BrdU, p27, GATA-4, Androgen Receptor), we investigated the SC differentiation status in 36 days old and adult Wistar rats, focusing mainly in the transition region (TR) between the seminiferous tubules (ST) and the rete testis. Our results showed that SCs in TR remain undifferentiated for a longer period and, although at a lesser degree, even in adult rats proliferating SCs were observed in this region. Therefore, these findings suggest that, different from the other ST regions investigated, SCs residing in the TR exhibit a distinct functional phenotype. These undifferentiated SCs may compose a subpopulation of SC progenitors that reside in a specific microenvironment capable of growing the ST length if needed from this particular testis region. Moreover, our findings demonstrate an important aspect of testis function in mammals and opens new venues for other experimental approaches to the investigation of SC physiology, spermatogenesis progression and testis growth. Besides that, the TR may represent an important site for pathophysiological investigations and cellular interactions in the testis.

Amifostine protective effect on cisplatin-treated rat testis

Cisplatin is a potent drug used in clinical oncology but causes spermatogenesis damage. Amifostine is a drug used against toxicity caused by ionizing irradiation and chemotherapeutic drugs. Since cisplatin provokes fertility and induces germ cell apoptosis and necrosis, we proposed to evaluate the amifostine cytoprotective action on testes of cisplatin-treated rats. Thirty-day-old prepubertal Wistar rats received a single cisplatin dose of 5 mg/kg and were killed after 3, 6, and 12 hr. The hematoxylin-eosin stained testicular sections were submitted to histological, morphometric, and stereological analysis. The terminal deoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick end-labeling (TUNEL) method was used to label apoptotic cells. TUNEL-positive and TUNEL-negative germ cells with abnormal nuclear morphology (ANM) were scored. Significant alterations of greater part of the parameters occurred in the cisplatin-treated group (CE) compared to the group that received amifostine before the cisplatin-treatment (ACE); however, testicular weight and volume did not vary between these groups. Tubular diameter was reduced in CE in comparison to ACE rats, while interstitial tissue and lymphatic space volume and volume density were significantly higher in CE rats; interstitial testicular edema probably occurred in cisplatin-treated rats. CE rats showed important histological alterations, which were more accentuated than in ACE rats. The numerical densities of apoptotic germ cells and TUNEL-negative cells with ANM were lower in ACE than in CE rats. In conclusion, the amifostine previously administered to prepubertal rats reduced the testicular damage caused by cisplatin. We conclude that amifostine partially protected the rat seminiferous epithelium against cisplatin toxicity.

C-terminal phosphorylation of murine testis-specific histone H1t in elongating spermatids

Previous studies gave differing results as to whether the testis-specific histone H1t was phosphorylated during rodent spermatogenesis. We show here that histones extracted from germ cell populations enriched with spermatids at different stages of development in rat testes reveal an electrophoretic shift in the position of H1t to slower mobilities in elongating spermatids as compared to that from preceding stages. Alkaline phosphatase treatment and radioactive labeling with (32)P demonstrated that the electrophoretic shift is due to phosphorylation. Mass spectrometric analysis of histone H1t purified from sexually mature mice and rat testes confirmed the occurrence of singly, doubly, and triply phosphorylated species, with phosphorylation sites predominantly found at the C-terminal end of the molecule. Furthermore, using collision-activated dissociation (CAD) and electron transfer dissociation (ETD), we have been able to identify the major phosphorylation sites. These include a new, previously unidentified putative H1t-specific cdc2 phosphorylation site in linker histones. The presence of phosphorylation at the C-terminal end of H1t and the timing of its appearance suggest that this post-translational modification is involved in the reduction of H1t binding strength to DNA. It is proposed that this could participate in the opening of the chromatin fiber in preparation for histone displacement by transition proteins in the next phase of spermiogenesis.

Rat testis as a radiobiological in vivo model for radionuclides

The radiobiological effect of intracellularly localised radionuclides emitting low energy electrons (Auger electrons) has received much attention. Most in vivo studies reported have been performed in the mouse testis. We have investigated the rat testis as an in vivo radiobiological model, with sperm-head survival, testis weight loss and also alteration in the blood plasma hormone levels of FSH and LH as radiobiological endpoints. Validation of the rat testis model was evaluated by using mean absorbed doses of up to 10 Gy from intratesticularly (i.t.) injected (111)In oxine or local X-ray irradiation. Biokinetics of the i.t. injected radionuclide was analysed by scintillation camera imaging and used in the absorbed dose estimation. By the analysis of the autoradiographs, the activity distribution was revealed. Cell fractionation showed (111)In to be mainly associated with the cell nuclei. External irradiations were monitored by thermoluminescence dosimeters. The sperm-head survival was the most sensitive radiobiological parameter correlated to the mean absorbed dose, with a D(37) of 2.3 Gy for (111)In oxine and 1.3 Gy for X rays. The levels of plasma pituitary gonadal hormones FSH and LH were elevated for absorbed doses >7.7 Gy. This investigation shows that the radiobiological model based on the rat testis has several advantages compared with the previously commonly used mouse testis model. The model is appropriate for further investigations of basic phenomena such as radiation geometry, intracellular kinetics and heterogeneity, crucial for an understanding of the biological effect of low-energy electrons.

Apoptosis and testicular alterations in albino rats treated with etoposide during the prepubertal phase

Etoposide is a podophyllotoxin semiderivative that is used in a variety of chemotherapy treatments, including therapy for children tumors. This drug promotes the formation of a ternary DNA-topoisomerase II-etoposide complex that triggers apoptosis. The purpose of this work was to analyze the occurrence of apoptosis in the seminiferous epithelium of prepubertal, pubertal, and adult rats treated with 10, 20, and 40 mg/Kg of etoposide during the prepubertal phase, as well as the role of apoptosis in etoposide-induced testicular damage. The rat testes were fixed in Bouin's liquid, and the apoptotic cells were quantified by means of the hematoxylin and eosin (H&E) technique (all groups) and the terminal dUTP nick end labeling (TUNEL) method (prepubertal groups only). The results obtained from both the H&E and TUNEL methods showed an increased frequency of apoptosis in the seminiferous epithelium of treated animals, except for the subgroup that received the 10-mg/Kg dose and was sacrificed 12 hr after the treatment and for the etoposide-treated pubertal group, that did not show cells suggesting apoptosis during H&E analysis. The labeled cells were mainly primary spermatocytes and differentiated spermatogonia. The prepubertal rats showed an etoposide-dose-dependent diminution of differentiated spermatogonia. Etoposide treatment during the prepubertal phase increases the frequency of apoptosis in the seminiferous epithelium, and causes serious harm to male fertility. 2004.

Expression of germ cell nuclear factor (GCNF/RTR) during spermatogenesis

Germ cell nuclear factor (GCNF/RTR), a novel orphan receptor in the nuclear receptor superfamily of ligand-activated transcription factors, is expressed predominantly in developing germ cells. In several mammalian species two GCNF/RTR mRNAs are present in the testis, with the smaller 2.3-kb transcript generally expressed at higher levels than the larger 7.4- or 8.0-kb transcript. In both the mouse and rat, the 2.3- and 7.4-kb GCNF/RTR transcripts were detected in isolated spermatogenic cells, but not in Sertoli cells. Expression of these transcripts is differentially regulated, with the larger 7.4-kb mRNA appearing earlier during testicular development. The major 2.3-kb transcript is expressed predominantly in round spermatids in the mouse and rat. In situ hybridization studies in the rat demonstrated that GCNF/RTR transcripts reach maximal steady-state levels in round spermatids at stages VII and VIII of the spermatogenic cycle, and then decline abruptly as spermatids begin to elongate. RNase protection assays were used to predict the 3' termination site of the 2.3-kb transcript. An alternative polyadenylation signal (AGUAAA) was identified just upstream of this termination site. These studies suggest that GCNF/RTR may regulate transcription during spermatogenesis, particularly in round spermatids just prior to the initiation of nuclear elongation and condensation.

Ontogeny of rat testicular mitogenic activity studied with transformed and nontransformed mouse 3T3 fibroblasts

The ontogeny of the testicular mitogenic activity of Sprague Dawley rats was evaluated by stimulation in vitro of [3H]thymidine uptake and cell number in Swiss 3T3 and transformed NIH 3T3 fibroblasts. Addition of various amounts of testicular cytosolic protein resulted in a dose-dependent increase in cell number in both cell lines. The [3H]thymidine responses to testicular cytosolic proteins was also dose dependent but in a nonparametric manner. In addition, the responses of 3T3 cells to testicular cytosol was apparently dependent on the developmental stage of the testis, the time of stimulation, and the proliferative nature of the fibroblast cell line. These results suggest the presence of multiple forms of mitogenic substance in testicular cytosol and imply that the relative amounts of these substances may depend on the age of the donor animal. These substances may be important in the proliferation or differentiation of cell types at various stages of testicular development.

Effect of hexavalent chromium on testicular maturation in the rat

Daily intraperitoneal administration of hexavalent chromium (Cr6+; 1, 2, and 3 mg/kg intraperitoneally as potassium dichromate) in weaned rats for an entire duration of 55 and 90 days of age produced dose- and duration-dependent enzymatic and pathologic alterations. At 55 days, the pathologic changes were not seen in testes of Cr6+ treated rats, but the activities of sorbitol dehydrogenase, lactic dehydrogenase, gamma-glutamyl transpeptidase, and glucose-6-phosphate dehydrogenase were significantly altered. When the treatment was prolonged to sexual maturity, that is, 90 days of age, the alterations in enzyme activities were greater, and there were dose-dependent pathologic changes in the testes of Cr(6+)-treated rats. These alterations suggest a risk to growing testes if rats are exposed to Cr6+ during the prepubertal stage of development, which, in turn, may disturb normal testicular physiology at adulthood.

Restricted lesions after testicular biopsies in young and adult rats

In order to evaluate the possible harmful effects of surgical removal of a testicular biopsy, adult and immature rats were subjected to unilateral testicular biopsy and were studied 2-4 months later. One group of adult rats were sham-operated. Perfusion-fixed, plastic-embedded specimens of the testes were examined by light microscopy. No morphological differences were found between rats that were immature and those that were adult at the time of biopsy. The lesions observed were focal and occurred only in the vicinity of the site of biopsy. Only about 0.5% (range 0.01-4.5) of the testis was affected. No morphological signs of any immune reaction were observed. It is suggested that the lesions are caused mainly by interference with local blood flow, and to a minor extent by disruption of the flow of seminiferous tubule fluid.

Expression of hsp70-related gene in developing and degenerating rat testis

Rat testes contain highly elevated levels of 2.5 kb RNA transcribed from a heat shock (hsp70) related gene. In the present paper northern blot analysis was used to follow the changes in the 2.5 kb transcript level during the postnatal development of rat testis and during the degeneration of the seminiferous epithelium in adult rats caused by experimental cryptorchidism. The 2.5 kb transcript was undetectable in newborn rats until the 3rd week of life. The level of the transcript reached a maximum at the 4th week and remained unchanged from that point on. Two days after the surgical translocation of the testes from the scrotum into the abdominal cavity the level of 2.5 kb transcript rapidly declined. Presented results strongly suggest that the hsp 70-like gene coding for the 2.5 kb RNA is specifically expressed in germinal cells, most probably in the spermatocytes.

Purine phosphoribosyltransferase (EC 2.4.2.7 and 2.4.2.8) and purine de novo synthesis activity in rat testicular tissue at different stages of development, and their correlation with the circulating levels of gonadotrophins and testosterone, and with structural changes

The overall activity of the purine de novo synthesis pathway and the activities of purine phosphoribosyltransferase in the rat testis were measured at different ages and were correlated with histological observations. Similar studies of the concentration of circulating gonadotrophins and testosterone were performed. The purine phosphoribosyltransferase activities were between two and three orders of magnitude greater than purine de novo synthesis. The peak activity of the purine de novo synthesis pathway coincided with the first appearance of meiosis in the spermatocytes immediately before the luteinising hormone (LH) level rose to its peak. The highest activity of the hypoxanthine phosphoribosyltransferase (HPRT; EC 2.4.2.8) - catalysed purine salvage pathway coincided with the first appearance of mature spermatozoa in the tubules just after the occurrence of peak levels of follicle-stimulating hormone (FSH). These findings are linked to the development of testicular atrophy in cases of severe HPRT deficiency in man.

Kinetics of di-(2-ethylhexyl) phthalate in immature and mature rats and effect on testis

The testicular response of di-(2-ethylhexyl) phthalate (DEHP), as well as the kinetics of DEHP and its primary metabolite mono-(2-ethylhexyl) phthalate (MEHP), were studied in immature and mature rats. After 14 daily oral doses of 1.0 g DEHP/kg body weight to 25, 40 and 60-day-old rats, testicular damage was observed in the youngest age group only. DEHP was not found to any significant extent in the peripheral plasma after an oral dose of 1.0 g DEHP/kg body weight. High plasma levels of MEHP were found, with maximal plasma concentrations ranging from 48 to 152 micrograms/ml. The in vitro plasma protein binding of MEHP was extensive, approximately 98%, in all age groups and no age-related difference in the elimination half-life was observed. The amount of DEHP-derived material excreted in urine was twice as high in 25 as in 60-day-old rats. The mean area under the plasma concentration-time curve of MEHP was also significantly larger in 25 than in 40 and 60-day-old rats. These observations suggest that the extent of absorption, and hence total exposure to MEHP and its metabolites, is higher in young than in more mature rats after oral administration of DEHP. It seems probable that this finding is relevant to the age-related difference in the toxic effects on the testis.

Maturation of the juvenile rat testis after surgical treatment of cryptorchidism

Rats were made bilaterally cryptorchid at 17 days of age and bilateral orchidopexy performed at 34 days of age. The epididymal content of androgen binding protein (ABP), the weight and morphology of the testis, the cross-sectional area of seminiferous tubules and the testicular concentration of testosterone were then studied at 34, 42, 59 and 120 days of age. Cryptorchidism was followed rapidly by progressive inhibition of spermatogenesis and testicular growth as well as by decreased Sertoli cell secretion of ABP. Orchidopexy resulted in a gradual restoration of spermatogenesis, and all impaired parameters seemed to improve at the same, fairly slow rate. Restoration was not complete, but by 120 days of age the morphological appearance of the testis was compatible with recovery of normal fertility.