Seasonally activated spermatogenesis is correlated with increased testicular production of testosterone and epidermal growth factor in mink (Mustela vison)

Spermatocytes are the terminals of germ cell differentiation in plateau zokor (Eospalax baileyi) during the non-breeding season

Plateau zokor (Eospalax baileyi) is a subterranean rodent and seasonal breeder. During the non-breeding season, the testicles regress, leading to the arrest of spermatogenesis and loss of fertility. The identification of the specific germ cell type at which spermatogenesis is arrested, as well as potential regulatory factors during the non-breeding season, is important for understanding seasonal spermatogenesis in subterranean species. This study analyzed genes in spermatocytes of plateau zokor by referring to single-cell RNA results in mice. We discovered that spermatogenesis is arrested at the spermatocyte during the non-breeding season, which was corroborated via immunofluorescence staining results. The analysis of gene expression during different stages of meiotic prophase I has revealed that germ cell development may be arrested, starting from zygonema, during the non-breeding season. Meanwhile, we discovered that the apoptosis genes were up-regulated, leading to apoptosis in spermatocytes. To confirm that the germ cell differentiation was blocked during the non-breeding season due to a decrease in the androgen level, we used androgen receptor antagonist (flutamide) to intervene in the breeding season and found that the inner diameter of the seminiferous tubules was significantly reduced, spermatogenesis was arrested, and spermatocytes underwent apoptosis. This study revealed that spermatocytes are the terminal of germ cell differentiation in plateau zokor during the non-breeding season and that the arrest of differentiation is attributed to a decline in androgen levels. Our results complement the theoretical basis of seasonal reproduction in plateau zokor.

Seasonal spermatogenesis in the red-eared slider (Trachemys scripta elegans): The roles of GnRH, actin cytoskeleton, and MAPK

Reproduction is the key to the ecological invasion of alien species. As an invasive species, the characteristic and regularity of red-eared slider (Trachemys scripta elegans) spermatogenesis is an index for evaluating reproduction and ecological adaptation. Here, we investigated the characteristics of spermatogenesis i.e., the gonadosomatic index (GSI), plasma reproductive hormone levels, and the histological structure of testes by HE and TUNEL staining, and then RNA-Seq in T. s. elegans. The histomorphological evidence confirmed that seasonal spermatogenesis in T. s. elegans has four successive phases: quiescence (December-May of the following year), early-stage (June-July), mid-stage (August-September), and late-stage (October-November). In contrast to 17β-estradiol, testosterone levels were higher during quiescence (breeding season) compared to mid-stage (non-breeding season). Based on RNA-seq transcriptional analysis, gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were used to analyze the testis in the quiescent and mid-stage. Our study found that circannual spermatogenesis is regulated by interactive networks including gonadotropin-releasing hormone (GnRH) secretion, regulation of actin cytoskeleton, and MAPK signaling pathways. Moreover, the number of genes associated with proliferation and differentiation (srf, nr4a1), cell cycle (ppard, ccnb2), and apoptosis (xiap) were up-regulated in the mid-stage. With the maximum energy saving, this seasonal pattern of T. s. elegans determines optimal reproductive success and thus adapts better to the environment. These results provide the basis for the invasion mechanism of T. s. elegans and lay the foundation for deeper insight into the molecular mechanism of seasonal spermatogenesis in reptiles.

Cell adhesion function was altered during the seasonal regression of the seminiferous epithelium in the mink species Neovison vison

Minks are seasonal breeders whose seminiferous epithelium undergoes regression through massive germ cell death, leaving only Sertoli cells and spermatogonial cells in the tubules. However, the molecular mechanisms that control this biological process remain largely unknown. This study describes a transcriptomic analysis of mink testes at various reproductive stages (active, regressing, and inactive). A comparison of seminiferous epithelium at different stages of reproduction shows that cell adhesion is altered during regression. In addition, genes and proteins involved in forming the blood-testis barrier (BTB) were examined in sexually active and inactive minks. The seminiferous epithelium in the testes of sexually inactive minks expressed occludin, but this expression was not discernibly observed in the testes of sexually active minks. There was no discernible expression of CX43 in the seminiferous epithelium in the testes of sexually inactive minks, but CX43 was expressed in the testes of sexually active minks. During the regression process, we observed a remarkable increase in the expression levels of Claudin-11, which is associated with Sertoli-germ cell junctions. In conclusion, these findings suggest a loss of Sertoli-germ cell adhesion, which may regulate postmeiotic cell shedding during testicular regression in mink.

Cellular Modifications in Spermatogenesis during Seasonal Testicular Regression: An Update Review in Mammals

Simple Summary

The most common form of reproduction in mammals is seasonal reproduction. This ensures that offspring are born at the most suitable time for survival, due to the abundance of food and the optimal temperatures for early postnatal development. In males, one way to achieve this is to decrease or lose fertility over a given period. This loss is associated with a greater or lesser degree of spermatogenesis modification that affects both germ and Sertoli cells. This paper reviews the different cellular mechanisms that have been postulated in recent years to explain how the activity of the seminiferous epithelium decreases during the non-reproductive period.

Abstract

Testicular regression occurs during the non-breeding season in many mammals. This affects spermatogenesis, resulting in decreased or arrested activity. Both lead to a decrease or cessation in sperm production. In recent years, the cellular mechanisms that lead to infertility in males in non-reproductive periods have been studied in very different species of mammals. At the start of the present century, the main mechanism involved was considered as an increase in the apoptotic activity of germ cells during the regression period. The loss of spermatogonia and spermatocytes causes not only a decrease in spermatogenesis, but an arrest of the seminiferous epithelium activity at the end of regression. Recently, in some mammal species, it was found that apoptosis is the usual mechanism involved in epithelium activity arrest, although it is firstly atrophied by massive desquamation of the germ cells that are released from their binding with the Sertoli cells, and which are shed into the lumen of the seminiferous tubule. In other species, it has been shown that not only germ cell apoptosis, but also Sertoli cell apoptosis, including decreased proliferative activity, spermatophagy or autophagy, are involved in testicular regression. Furthermore, the most recent studies indicate that there are multiple patterns of seminiferous epithelium regression in seasonally breeding animals, which may not only be used by different species, but also by the same ones to reproduce in the best conditions, ensuring their survival. In conclusion, at this time, it is not possible to consider the existence of a paradigmatic cellular mechanism in the involution of the seminiferous epithelium applicable to all male mammals with seasonal reproduction, rather the existence of several mechanisms which participate to a greater or lesser extent in each of the species that have been studied to date.

Multiple types of genomic variation contribute to adaptive traits in the mustelid subfamily Guloninae

Species of the mustelid subfamily Guloninae inhabit diverse habitats on multiple continents, and occupy a variety of ecological niches. They differ in feeding ecologies, reproductive strategies and morphological adaptations. To identify candidate loci associated with adaptations to their respective environments, we generated a de novo assembly of the tayra (Eira barbara), the earliest diverging species in the subfamily, and compared this with the genomes available for the wolverine (Gulo gulo) and the sable (Martes zibellina). Our comparative genomic analyses included searching for signs of positive selection, examining changes in gene family sizes, as well as searching for species-specific structural variants (SVs). Among candidate loci associated with phenotypic traits, we observed many related to diet, body condition and reproduction. For example, for the tayra, which has an atypical gulonine reproductive strategy of aseasonal breeding, we observe species-specific changes in many pregnancy-related genes. For the wolverine, a circumpolar hypercarnivore that must cope with seasonal food scarcity, we observed many changes in genes associated with diet and body condition. All types of genomic variation examined (single nucleotide polymorphisms, gene family expansions, structural variants) contributed substantially to the identification of candidate loci. This strongly argues for consideration of variation other than single nucleotide polymorphisms in comparative genomics studies aiming to identify loci of adaptive significance.

Seasonal expressions of ERα, ERβ, EGF, EGFR, PI3K and Akt in the scent glands of the muskrats (Ondatra zibethicus)

Epidermal growth factor (EGF) is an important autocrine and/or paracrine mediator of steroid hormones to stimulate growth and differentiation in mammals. The aim of this study is to investigate seasonal expressions of estrogen receptor α (ERα), estrogen receptor β (ERβ), EGF, epidermal growth factor receptor (EGFR), phosphatidylinositol 3-kinase (PI3K) and protein kinase B (Akt) in the scent glands of the muskrats during the breeding and non-breeding seasons. Histologically, three types of cells including the glandular cells, interstitial cells and epithelial cells were identified in the scent glands in both seasons. Immunohistochemical results showed that ERα, ERβ, EGF, EGFR, PI3K and Akt were presented in the different types of cells of the scent glands during the breeding and non-breeding seasons. Transcriptome data of the scent glandular tissues from muskrats in the breeding and non-breeding seasons showed that differential seasonal changes might be related to the estrogen-EGFR signaling pathway. The gene expression levels of ERα, ERβ, EGF, EGFR, PI3K were increased, while the gene expression level of Akt were decreased in the breeding season than those in the non-breeding season. Besides, the concentrations of 17β-estradiol (E₂) in the serum and the scent glandular tissues were remarkably higher in the breeding season than those of the non-breeding season. Taken together, our results suggested that EGFR signaling pathway may coordinate with ERs signaling to regulate the seasonal changes of the scent glandular functions.

Platelet-derived growth factor-BB and epidermal growth factor promote dairy goat spermatogonial stem cells proliferation via Ras/ERK1/2 signaling pathway

Spermatogonial stem cells (SSCs) have been used for the production of transgenic animals and for the recovery of male fertility. However, the proliferation of SSCs in vitro is still immature, and the mechanisms and pathways involved in the proliferation of SSCs are not clear. Here, the effects of platelet-derived growth factor-BB (PDGF-BB) and epidermal growth factor (EGF) on the proliferation of dairy goat SSCs in vitro were detected. The results showed that 20 ng/ml PDGF-BB or 25 ng/ml EGF was the optimum concentration, and that the BCL2 in the experimental groups was significantly higher than that in the control (P < 0.05), while BAX and BAD were dramatically downregulated (P < 0.05). The pERK1/2 in the experimental groups was about 3-5 times higher than that in the control. After the specific MEK1/2 inhibitor was added, BCL2 was reduced significantly (P < 0.001), while BAX and BAD were upregulated (P < 0.001). The expression of pERK1/2 decreased by 10%-30%. We speculated that these two growth factors may be mediated through the Ras/ERK1/2 signaling pathway to regulate the expression of pERK1/2 protein, and thus enhance the resistance of SSCs to apoptosis. However, further studies are needed to verify this hypothesis.

Noninvasive monitoring of female reproductive hormone metabolites in the endangered European mink (Mustela lutreola)

This study examined the reproductive physiology of female European mink (Mustela lutreola) to augment the available information on estrus, ovulation, and pregnancy with the long-term goal of supporting ex situ breeding management of this highly endangered species. Fecal reproductive hormone metabolites were measured using EIAs for estrogen and 20-oxo-pregnane metabolites. Seasonal hormone profiles were established. A comparison of hormone fluctuations in pregnant and nonpregnant females showed that both estrogen and 20-oxo-pregnane metabolites were significantly elevated during gestation, which is 42 days in length. Delayed implantation or embryonic diapause does not occur in this species. Litter size was correlated with 20-oxo-pregnane levels but not with estrogen concentrations. During lactation, 20-oxo-pregnane metabolite levels remained higher than in nonpregnant females. The breeding season was characterized by peaks in vaginal cornified cells and fecal estrogen metabolite levels. Up to four peaks in estrogen levels were identified and confirmed that European mink are seasonally polyestrous. The results of 20-oxo-pregnane measurements indicated that hCG can be applied to induce ovulation. With the establishment of this noninvasive method, we present a new tool to support population management of this species.

Expression profiles of relaxin family peptides and their receptors indicate their influence on spermatogenesis in the domestic cat (Felis catus)

Disturbed spermatogenesis is a common problem in felines. Studying spermatogenesis in the domestic cat can improve the understanding of the biological background and help to counteract fertility problems in other feline species. Here, we analyzed 3 relaxin family peptides (relaxin, relaxin-3, and INSL3) and their receptors (RXFP1, RXFP2, and RXFP3) as potential spermatogenic factors involving their expression in the testis at different stages of its development. It may be concluded from its stage-dependent expression that relaxin, together with RXFP1, appears to be involved in the first stage of spermatogenesis, whereas relaxin-3 via binding to RXFP3 influences spermiogenesis. Furthermore, correlations were observed between relaxin, relaxin-3, RXFP1, RXFP2 and RXFP3 messenger RNA expression, and the relative numbers of haploid cells in testes. The peptide INSL3 was highly expressed at all testis development stages. Because of the low and stage-independent expression of its receptor RXFP2, an auto- and/or paracrine function of INSL3 in spermatogenesis seems unlikely. In the adult testis, messenger RNA expression of relaxin, RXFP1, and RXFP3 predominantly occurs in the tubular testis compartment, whereas INLS3 is mainly expressed in the interstitium.

Epidermal growth factor mediates spermatogonial proliferation in newt testis

The complex processes of spermatogenesis are regulated by various factors. The aim of the current study is to determine the effect of epidermal growth factor (EGF) on spermatogonial proliferation and clarify the mechanism causing the proliferation in newt testis. In the organ culture, EGF stimulated spermatogonial proliferation, but not their differentiation into spermatocytes. cDNA cloning identified 3 members of the EGF receptors, ErbB1, ErbB2, and ErbB4, in the testis. RT-PCR showed that all the receptors cloned were expressed in both Sertoli and germ cells at the spermatogonial stage. In the organ cultures with inhibitors for the EGF receptors, mitogen-activated protein kinase (MAPK), and phosphoinositide 3-kinase (PI3K), the EGF-induced spermatogonial proliferation was suppressed. Furthermore, when the organ culture was exposed to EGF, the expressions of stem cell factor (SCF), immunoglobulin-like domain containing neuregulin1 (Ig-NRG1), and ErbB4 mRNA were increased. These results suggested that, since the spermatogonia are sequestered within cysts by the blood-testis barrier consisted of Sertoli cells, EGF possibly mediates spermatogonial proliferation in an endocrine manner through the receptors including ErbB1, ErbB2, and ErbB4 expressed on Sertoli cells via activation of MAPK cascade or/and PI3K cascade by elevating the expressions of SCF, Ig-NRG1, and ErbB4.