The seasonal profile of proliferation and apoptosis in the prostate gland of the wild ground squirrel (Spermophilus dauricus)

Epithelial-mesenchymal transition during the growth and involution of the prostate gland in wild ground squirrels (Spermophilus dauricus)

The prostate glands of wild ground squirrels display enlarged volume during the breeding season and shrunk size during the nonbreeding season, which enables the wild ground squirrel to be an ideal animal model for studying the mechanisms of prostate growth and involution. To clarify the possible mechanism underlying seasonal morphological changes of the prostate in wild ground squirrels, epithelial-mesenchymal transitions (EMT) were focused, and the expression of EMT-related genes was investigated in the current study. Histological results showed that the epithelial lumen enlarged in the breeding season, and the stromal cells expanded during the non-breeding season. Transcriptomic analysis showed 132 EMT-related genes expressed differentially in the prostate during breeding versus non-breeding seasons, indicating EMT might occur during the morphological changes of the prostate. To further confirm the EMT process, the immunolocalizations of EMT markers were inspected, which showed the positive staining of E-cadherin, Claudin-1, ZO1, β-catenin, N-cadherin, VIMENTIN, SLUG, and ZEB1 were presented in epithelial and/or stromal cells. The expressions of Cdh1, Cldn, Tjp1, Ctnnb1, and Snai2 increased in the prostate of the breeding season, while the expressions of Cdh2, Vim, and Zeb1 reduced in the prostate of the breeding season. Moreover, the expression levels of the epithelial marker Cdh1 and the mesenchymal markers Cdh2 and Vim were found to be positively or negatively correlated with prostate weight, respectively. In conclusion, the current results suggested that the EMT might be responsible for prostate growth and involution in the wild ground squirrel.

The effects of low ambient temperature on steroidogenesis and mitochondrial functions in the testes of wild ground squirrels (Spermophilus dauricus)

Seasonal reproduction is a widely used breeding strategy in wildlife, especially vertebrates inhabiting temperate regions. Generally, ambient temperature is considered a significant factor influencing the reproductive status of animals. In the present study, wild ground squirrels (Spermophilus dauricus), typical seasonal breeders, were used as an animal model to investigate the mechanism behind the impact of low ambient temperature on testicular function. To simulate the winter environment of wild ground squirrels, we lowered the temperature gradient in the rearing environment to 4 °C. At sampling, the body surface temperature of the squirrels reared under normal ambient temperature (22 °C, NAT group) and the low ambient temperature (4 °C, LAT group) were 31.5 °C and 22.8 °C, respectively. Subsequently, we conducted immunohistochemical assays, qPCR, and enzyme-linked immunosorbent assays (ELISA) to examine the variations in testicular functions, as well as the dynamics and functions of mitochondria, in the squirrels of NAT and LAT groups. As a result, the levels of positive immunostaining for PCNA, P21, and P27 were significantly lower in the testes of LAT group, while the levels of immunostaining for Cleaved Caspase-3 and TUNEL were significantly higher. In addition, the low-temperature treatment reduced the expression level of steroidogenesis-related genes, including LHR, FSHR, GATA-4, P450scc, and P450arom, and decreased the testosterone concentration. Moreover, markers of mitochondrial fission and fusion, DRP1 and MFN2, respectively, were increased in the testes of LAT group. Additionally, the mRNA level of SOD1 was notably higher in the testes of LAT group. In conclusion, the low ambient temperature inhibited spermatogenesis, steroidogenesis, as well as mitochondrial dynamics and functions in the testes of wild ground squirrels.

Seasonal changes in endoplasmic reticulum stress and steroidogenesis in the ovary of the wild ground squirrels (Citellus dauricus Brandt)

The development of the follicle is accompanied by steroidogenesis and secretion, the endoplasmic reticulum (ER) requires significant synthesis of relevant proteins to support changes in the follicular microenvironment. The aim of this study was to investigate whether seasonal changes in gonadotropins and ovarian steroid hormones in the wild ground squirrels induce endoplasmic reticulum stress (ERS) and changes in ERS-mediated unfolded protein response (UPR) signaling. There were significant seasonal differences in ovarian mass, with values higher in the breeding season and relatively low in the non-breeding season. Histological observations revealed that ovaries in the breeding season had germ cells including primordial follicles, primary follicles, secondary follicles, tertiary follicles, and the corpus luteal, whereas ovaries consisted mainly of primary and secondary follicles in the non-breeding season. Analysis of ovarian transcriptome data showed that 1298 genes were up-regulated in expression and 1432 genes were down-regulated in expression during both periods. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis indicated that these genes were mainly enriched in estrogen signaling pathways, ovarian steroidogenesis and endoplasmic reticulum protein processing pathways. The expression levels of steroidogenic enzymes (P450scc, P450c17, 3β-HSD, and P450arom) and gonadotropin receptor (FSHR and LHR) were significantly increased during the breeding season compared to the non-breeding season. GRP78 and UPR signaling factors (ATF4, ATF6, XBP1s) associated with ERS were expressed in both seasons. The mRNA expressions of Atf6 and Xbp1s were higher in the breeding season than those of the non-breeding season. Conversely, Atf4 and its downstream homologous protein (Chop) exhibited higher expression during the non-breeding season. In addition, follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol-17β, and progesterone of serum were significantly higher in the breeding season than those of the non-breeding season. These results suggested that UPR signaling, associated with seasonal changes in ovarian steroidogenesis, was activated during the breeding season and that ERS might be involved in regulating seasonal changes in ovarian steroidogenesis in the wild ground squirrels.

Seasonal Change in Adiponectin Associated with Ovarian Morphology and Function in Wild Ground Squirrels (Citellus dauricus Brandt)

The goal of this study is to explore the relationship between altered circulating adiponectin concentration, ovarian tissue morphology, ovarian steroidogenesis, and sex hormone production in ovaries of wild ground squirrels. The ovarian mass differed significantly during the breeding and non-breeding seasons, and the circulating estradiol and progesterone concentrations were significantly higher in the breeding season, while the circulating adiponectin level was significantly lower. The expression levels of gonadotropin receptors (FSHR and LHR) and steroidogenic enzymes (StAR, P450scc, P450arom, and 3β-HSD) were significantly higher during the breeding season. Comparing the ovarian transcriptome data of wild ground squirrels between the two periods, we found that some differentially expressed genes were enriched for ovarian steroidogenesis and the adipocytokine signaling pathway, which correlated with our present results. Notably, the MAPK signaling pathway was also enriched and its related genes (Erk1, p38 Mapk, Jnk) were up-regulated by qPCR during the non-breeding season. These findings suggested that adiponectin may be involved in the regulation of seasonal changes in the ovarian function of wild ground squirrels, possibly by acting on the MAPK signaling pathway to regulate sex steroidogenesis in the ovaries.

Estrogen signaling regulates seasonal changes of the prostate in wild ground squirrels (Spermophilus dauricus)

Previous studies found that testosterone was converted to dihydrotestosterone under the catalysis of 5α-reductase in the prostate of the wild ground squirrels. As a result, this study explored further whether testosterone could be converted to estrogen to affect the prostate gland function in wild ground squirrels. Histological observation showed that the area of epithelial cells and the prostatic secretory lumen were enlarged significantly during the breeding period. Transcriptome analysis revealed that the differentially expressed genes in the prostate were concentrated in the estrogen signaling pathway. Immunohistochemical analysis showed that the immunoreactivities of P450arom were detected in the stromal cells during the breeding and non-breeding periods, indicating the possible conversion of androgen into estrogen locally. Moreover, the immunolocalizations of ERα and ERβ were detected mainly in the epithelial or stromal cells. Additionally, qPCR analysis displayed that the mRNA expression level of P450arom in the prostate was significantly higher during the breeding period than that in the non-breeding period. Consistently, the concentration of 17β-estradiol (E₂) was higher in the prostate during the breeding period than the non-breeding period, which is positively correlated with the seasonal changes of prostatic weight. In conclusion, the present results indicated that estrogen produced by P450arom presented in stromal cells might regulate the growth and function of the prostate gland via the locally expressed estrogen receptors in wild ground squirrels. The results of this study were momentous for further uncovering the mechanism of the seasonal regulated by signal pathways in the prostate of wild ground squirrels.