Characteristics of seasonal spermatogenesis in the soft-shelled turtle

Seasonal modulation of the testis transcriptome reveals insights into hibernation and reproductive adaptation in Onychostoma macrolepis

The Onychostoma macrolepis have a unique survival strategy, overwintering in caves and returning to the river for reproduction in summer. The current knowledge on the developmental status of its testes during winter and summer is still undiscovered. We performed RNA-seq analysis on O. macrolepis testes between January and June, using the published genome (NCBI, ASM1243209v1). Through KEGG and GO enrichment analysis, we were able to identify 2111 differentially expressed genes (DEGs) and demonstrate their functions in signaling networks associated with the development of organism. At the genomic level, we found that during the overwintering phase, genes associated with cell proliferation (ccnb1, spag5, hdac7) were downregulated while genes linked to testicular fat metabolism (slc27a2, scd, pltp) were upregulated. This indicates suppression of both mitosis and meiosis, thereby inhibiting energy expenditure through genetic regulation of testicular degeneration. Furthermore, in January, we observed the regulation of autophagy and apoptosis (becn1, casp13), which may have the function of protecting reproductive organs and ensuring their maturity for the breeding season. The results provide a basis for the development of specialized feed formulations to regulate the expression of specific genes, or editing of genes during the fish egg stage, to ensure that the testes of O. macrolepis can mature more efficiently after overwintering, thereby enhancing reproductive performance.

Comparative genomic survey and functional analysis of DKKL1 during spermatogenesis in the Chinese soft-shelled turtle (Pelodiscus sinensis)

A feature of the Chinese soft-shelled turtle (Pelodiscus sinensis) is seasonal spermatogenesis; however, the underlying molecular mechanism is not well clarified. Here, we firstly cloned and characterized P. sinensis DKKL1, and then performed comparative genomic studies, expression analysis, and functional validation. P. sinensis DKKL1 had 2 putative N-glycosylation sites and 16 phosphorylation sites. DKKL1 also had classic transmembrane structures that were extracellularly localized. DKKL1's genetic distance was close to turtles, followed by amphibians and mammals, but its genetic distance was far from fishes. DKKL1 genes from different species shared distinct genomic characteristics. Meanwhile, they were also relatively conserved among themselves, at least from the perspective of classes. Notably, the transcription factors associated with spermatogenesis were also identified, containing CTCF, EWSR1, and FOXL2. DKKL1 exhibited sexually dimorphic expression only in adult gonads, which was significantly higher than that in other somatic tissues (P < 0.001), and was barely expressed in embryonic gonads. DKKL1 transcripts showed a strong signal in sperm, while faint signals were detected in other male germ cells. DKKL1 in adult testes progressively increased per month (P < 0.05), displaying a seasonal expression trait. DKKL1 was significantly downregulated in testes cells after the sex hormones (17β-estradiol and 17α-methyltestosterone) and Wnt/β-catenin inhibitor treatment (P < 0.05). Likewise, the Wnt/β-catenin inhibitor treatment dramatically repressed CTCF, EWSR1, and FOXL2 expression. Conversely, they were markedly upregulated after the 17β-estradiol and 17α-methyltestosterone treatment, suggesting that the three transcription factors might bind to different promoter regions, thereby negatively regulating DKKL1 transcription in response to the changes in the estrogen and androgen pathways, and positively controlling DKKL1 transcription in answer to the alterations in the Wnt/β-catenin pathway. Knockdown of DKKL1 significantly reduced the relative expression of HMGB2 and SPATS1 (P < 0.01), suggesting that it may be involved in seasonal spermatogenesis of P. sinensis through a positive regulatory interaction with these two genes. Overall, our findings provide novel insights into the genome evolution and potential functions of seasonal spermatogenesis of P. sinensis DKKL1.

HISTOLOGIC ANALYSIS OF TESTICULAR DEVELOPMENT AND SEXUAL MATURATION IN REHABILITATED NORTHERN SEA OTTERS (ENHYDRA LUTRIS KENYONI)

As part of routine captive management of the species, sea otter (Enhydra lutris) males are often castrated to prevent reproduction, to preserve limited spaces for future nonreleasable stranded individuals, and to minimize potential aggression among cohorts. To determine the relative stage of testicular development, testicles from 14 castrated, rehabilitated northern sea otters (Enhydra lutris kenyoni) were submitted for histologic examination. Eight of the otters (aged 201, 304, 344, 352, 360, 373, 401, and 1,423 d old) had evidence of varying degrees of sexual maturity. Histologic grading of maturity of individual testicles showed inactive testes, spermatocytes with some maturation of spermatogenic precursors, and fully active spermatogenesis. Spermatozoa were seen in the otters that were 401 and 1,423 d old (1.1 and 3.9 yr old). Sexual maturity for wild male sea otters in Alaska has been previously reported to occur from 3 to 5-6 yr. Social maturity, or the ability to breed and reproduce, may occur a few years later than the onset of physiologic maturity; age, weight, territory quality, and the length of time holding a territory may influence a male otter's mating success. Early testicular development in rehabilitated sea otters may be related to abundant resources, lack of competition, and decreased environmental pressures. Additionally, these findings have implications for husbandry and management practices in short- and long-term care facilities.

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.

Seasonal spermatogenesis, epididymal storage, and creatine kinase expression in Pelodiscus sinensis

The soft-shelled turtle, Pelodiscus sinensis, is an important economic aquaculture species. Its reproduction exhibits seasonality; however, there is a lack of systematic studies focused on sperm maturation and epididymal storage. The testes and epididymides of P. sinensis were sampled from March to December. The seasonal reproduction and maturation of the spermatozoa were examined by anatomy, hematoxylin and eosin staining, AB-PAS staining, and immunohistochemistry. Spermatogenesis exhibited obvious seasonality in P. sinensis. It was found that the spermatogenic epithelium was most active during June to September, whereas the diameter of the epididymal tubules was smallest during June to October. As key enzymes of ATP metabolism, creatine kinases were highly expressed in the epididymal tubule epithelium during the breeding season, which may be important for the regulation of sperm maturation. In addition, the epididymal tubule epithelium changed with the season in June to September, the epididymal tubule epithelium proliferated to form villous structures, and secreted a large number of glycoproteins, which may be related to the rapid maturation of sperm during the breeding season. In conclusion, this study provided insights into the spermatogenesis of P. sinensis through histological analysis and enriched our understanding of reproduction in reptiles.

Proliferation and Apoptosis of Cat (Felis catus) Male Germ Cells during Breeding and Non-Breeding Seasons

Simple Summary

Spermatogenesis is a complex process through which male gametes, spermatozoa, are produced starting from stem germ cells called spermatogonia. The existing information on cat spermatogenesis is limited and somewhat contradictory. In fact, although this species is considered a long-day breeder with a reproduction period starting when the day length increases and ending in late autumn, spermatogenesis and sperm production occur throughout the year. In order to assess whether cat spermatogenesis is modulated according to a season pattern, we analyzed testes taken from feral cats orchiectomized during reproductive (February–July) and non-reproductive (November and December) periods. The results of the analyses carried out in the present study showed that spermatogonial proliferation was more intense during the reproductive period and germ cell death via apoptosis (a programmed form of cell death) increased during the non-reproductive period. Our results confirm the hypothesis that cat spermatogenesis is seasonally modulated through changes of germ cell proliferation and apoptosis, according to a common paradigm of seasonally breeding species.

Abstract

The domestic cat (Felis catus) is a seasonal-breeding species whose reproductive period starts when the day length increases. Since the existing information on cat spermatogenesis is limited and somewhat contradictory, in the present study, germ cell proliferation and apoptosis in feral adult tomcats orchiectomized during reproductive (reproductive group, RG; February–July) and non-reproductive (non-reproductive group, NRG; November and December) seasons were compared. Cross-sections taken from the middle third of the left testis were chemically fixed and embedded in paraffin wax. Histological sections were processed for the immunohistochemical detection of proliferating germ cells (PCNA) and for the identification of apoptotic cells (TUNEL method). The percentage of PCNA-positive spermatogonia was higher in the RG than in the NRG. On the contrary, germ cell apoptosis was higher in the NRG than in the RG. Our results confirm that cat spermatogenesis is modulated on a seasonal basis and suggests that spermatogenesis control involves changes in germ cell proliferation and apoptosis according to a common paradigm of seasonally breeding species.

Male reproductive cycle in a population of the endemic butterfly lizard, Leiolepis ocellata Peters, 1971 (Squamata: Agamidae) from northern Thailand

Background

Fundamental knowledge on the seasonal reproductive microanatomy and endocrinology of reptiles has been collected from several studies of various species. The present study was to determine annual changes in hormonal profiles, and detailed histomorphometric and histochemical characteristics of the entire male reproductive system of the tropical agamid lizard, Leiolepis ocellata.

Results

Male L. ocellata individuals (n = 75) collected from the territory of two provinces (Lampang and Tak) in northern Thailand exhibited annual variation in sex hormonal, histomorphometric, and histochemical characteristics of the male reproductive system. The reproductive cycle was subdivided into eight reproductive periods (early first active, first active, resting, second recrudescent, second active, regressive, quiescent, and first recrudescent), thus displaying a bimodal pattern with two actively reproductive periods. Circulating sex hormones (testosterone, estradiol, and progesterone) peaked in the first active (February) and the second active (June–July) periods. Likewise, gonadosomatic index (GSI) and histomorphometric variables of the testes and of the genital ducts (rete testis, ductuli efferentes, ductus epididymis, and ductus deferens) revealed their highest values in the first active period. Marked increase in protein and carbohydrate production was detectable in the ductuli efferentes during the active periods.

Conclusions

The male reproductive cycle of L. ocellata showed a biannual pattern of the hormonal profile, and detailed histomorphometric and histochemical characteristics of the entire reproductive system. Hence, the present study provides improved basic knowledge on the reptilian reproductive biology with comparative viewpoints to other reptiles.

Expression and Characterization of the Spats1 Gene and Its Response to E2/MT Treatment in the Chinese Soft-Shelled Turtle (Pelodiscus sinensis)

Spats1 (spermatogenesis-associated, serinerich 1) has been characterized as a male-biased gene which acts an important role in the germ cell differentiation of mammals. Nevertheless, the function of Spats1 in the Chinese soft-shelled turtle (P. sinensis) has not yet been reported. To initially explore the expression of Spats1 in P. sinensis and its response to sex steroid treatment, we cloned the CDS of Spats1 for the first time and analyzed its expression profile in different tissues, including the testes in different seasons. The Spats1 cDNA fragment is 1201 base pairs (bp) in length and contains an open reading frame (ORF) of 849 bp, which codes for 283 amino acids. Spats1 mRNA was highly expressed in the testes (p < 0.01) and barely detectable in other tissues. In P. sinensis, the relative expression of Spats1 also responsive to seasonal changes in testis development. In summer (July) and autumn (October), Spats1 gene expression was significantly higher in the testes than in other seasons (p < 0.05). Spats1 mRNA was found to be specifically expressed in germ cells by chemical in situ hybridization (CISH), and it was mainly located in primary spermatocytes (Sc1), secondary spermatocytes (Sc2) and spermatozoa (St). Spats1 expression in embryos was not significantly changed after 17α-methyltestosterone (MT)and 17β-estradiol (E2) treatment. In adults, MT significantly induced Spats1 expression in male P. sinensis. However, the expression of Spats1 in testes was not responsive to E2 treatment. In addition, the expression of Spats1 in females was not affected by either MT or E2 treatment. These results imply that Spats1 is a male-specific expressed gene that is mainly regulated by MT and is closely linked to spermatogenesis and release in P. sinensis.

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.

The Seasonal and Stage-Specific Expression Patterns of HMGB2 Suggest Its Key Role in Spermatogenesis in the Chinese Soft-Shelled Turtle (Pelodiscus sinensis)

HMGB2, a member of the high-mobility group (HMG) proteins, was identified as a male-biased gene and plays a crucial role in the germ cells differentiation of mammals. However, its role in spermatogenesis of turtle is still poorly understood. Here, we cloned the Pelodiscus sinensis HMGB2 and analyzed its expression profile in different tissues and in testis at different developmental ages. P. sinensis HMGB2 mRNA was highly expressed in the testis of 3-year-old turtles (P < 0.01), but was hardly detected in ovaries and other somatic tissues. The results of chemical in situ hybridization (CISH) showed that HMGB2 mRNA was specifically expressed in germ cells, where it was mainly distributed in round spermatids and sperm, but not detected in somatic cells, spermatogonia, primary spermatocytes, or secondary spermatocyte. The relative expression of HMGB2 also responded to seasonal changes in testis development in P. sinensis. In different seasons of the year, the relative expression of HMGB2 transcripts in the testis of 1 year and 2 year olds showed an overall upward trend, whereas, in the testis of 3 year old, it peaked in July and then declined in October. Moreover, in April and July, with an increase in ages, the expression of HMGB2 transcripts showed an upward trend. However, in January and October, there was a decline in expression in testis in 3-year-old turtles. These results showed that HMGB2 is closely related to spermatogenesis in P. sinensis.

Extracellular vesicles in the male reproductive tract of the softshell turtle

Extracellular vesicles (EVs) are a heterogeneous group of cell-derived membranous structures comprising exosomes and microvesicles that originate from the endosomal system or are shed from the plasma membrane respectively. As mediators of cell communication, EVs are present in biological fluids and are involved in many physiological and pathological processes. The role of EVs has been extensively investigated in the mammalian male reproductive tract, but the characteristics and identification of EVs in reptiles are still largely unknown. In this review we focus our attention on EVs and their distribution in the male reproductive tract of the Chinese softshell turtle Pelodiscus sinensis , mainly discussing the potential roles of EVs in intercellular communication during different phases of the reproductive process. In softshell turtles, Sertoli-germ cell communication via multivesicular bodies can serve as a source of EVs during spermatogenesis, and these EVs interact with epithelia of the ductuli efferentes and the principal cells of the epididymal epithelium. These EVs are involved in sperm maturation, transport and storage. EVs are also shed by telocytes, which contact and exchange information with other, as well as distant interstitial cells. Overall, EVs play an indispensable role in the normal reproductive function of P. sinensis and can be used as an excellent biomarker for understanding male fertility.