Seasonal expression of P450c17 and 5α-reductase-2 in the scented gland of male muskrats (Ondatra zibethicus)

Seasonal expressions of nerve growth factor (NGF), and its receptor TrkA and p75 in the scent glands of muskrats (Ondatra zibethicus)

NGF, also known as nerve growth factor, is crucial for the survival and differentiation of the nervous system, in addition to being involved in a number of non-neuronal systems. The aim of this work was to investigate the immunolocalization and expression patterns of NGF, its receptor, tyrosine kinase receptor A (TrkA), and p75 in the scent glands of muskrats (Ondatra zibethicus) throughout the breeding and non-breeding seasons. The scent gland mass showed considerable seasonal variations, with higher values during the breeding season and comparatively lower levels during the non-breeding season. While no immunostaining was observed in the interstitial cells, NGF, TrkA, and p75 were immunolocalized in the scent glandular cells and epithelial cells during both breeding and non-breeding seasons. NGF, TrkA, and p75 protein and mRNA expression levels were higher in the scent glands during breeding season compared to the non-breeding season. Circulating levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone (T), and T in the scent gland were all significantly higher throughout the breeding season. The relative levels of the hormones in the plasma and the scent glands as well as NGF, TrkA, and p75 were positively associated with each other. Additionally, transcriptome analysis of the scent glands revealed that differentially expressed genes may be linked to steroid biosynthesis, the estrogen signaling pathway, and neurotransmitter transmembrane transporter function. These results suggest a potential role for NGF, TrkA, and p75 in controlling seasonal variations in the muskrats' scent gland functioning.

Seasonal expressions of the translocator protein (18 kDa), voltage-dependent anion channel, and steroidogenic acute regulatory protein in the scent glands of muskrats (Ondatra zibethicus)

Steroidogenesis machinery involves the steroidogenic acute regulatory protein (StAR), which regulates cholesterol transfer within the mitochondria, and the transport of cholesterol via a channel composed of 18-kDa translocator protein (TSPO), the voltage-dependent anion channel (VDAC) plus some accessory proteins. In this study, we investigated the immunolocalizations and expressions of StAR, TSPO, VDAC and cytochrome P450 side chain cleavage enzyme (P450scc, CYP11A1) in the scent glands of muskrats (Ondatra zibethicus) during the breeding and non-breeding periods. StAR, TSPO, VDAC and CYP11A1 were immunolocalized in the scent glandular, interstitial and epithelial cells in both breeding and non-breeding seasons with stronger immunostaining in the breeding season. The mRNA expression levels of StAR, TSPO, VDAC and CYP11A1 were higher in the scent glands of the breeding season than those of the non-breeding season. The circulating follicle stimulating hormone (FSH), luteinizing hormone (LH) and testosterone (T) as well as scent glandular T and dihydrotestosterone (DHT) concentrations were also significantly higher in the breeding season. Additionally, the transcriptomic study in the scent glands identified that differentially expressed genes might be related to the lipid metabolic process, integral component of membrane, and steroid hormone receptor activity and hormone activity using GO analysis. Further in vitro study verified that StAR, TSPO, VDAC and CYP11A1 expression levels increased significantly after human chorionic gonadotropin, hCG/FSH treatment compared with the control group. The KEGG pathway enriched by differentially expressed genes detected to be involved in endocrine system or amino acid metabolism. These findings suggested that the scent glands of the muskrats have ability to synthesize steroids de novo, and that the steroid hormones may have an important regulatory role in the scent glandular function via an autocrine/paracrine pathway.

Seasonal change of circulating leptin associated with testicular activities of the wild ground squirrels (Citellus dauricus)

The purpose of this study was to explore the variations in the circulating leptin concentrations of the wild ground squirrels in relation to seasonal changes in testicular activities. Hematoxylin-eosin staining showed all types of elongated spermatids and spermatogenic cells existed in the testis in April, while the primary spermatocytes and spermatogonia were most advanced stages of germ cells in June. In addition, the primary spermatocytes, secondary spermatocytes, and spermatogonia were most advanced stages of germ cells in September. The highest circulating leptin concentration was consistent with the maximum body weight results from accumulation of adipose tissue in September. The mRNA expression level of leptin receptor (Ob-R) and STAT3 was lowest in June, raised in September, and remained increased in April. Ob-R and STAT3 were stronger staining in the Leydig cells in July. Moreover, the concentrations of testosterone (T) showed the maximum values in April, the minimum values in June, and significant increases in September. Furthermore, it is worth noting that the levels of T increased with the mRNA levels of Ob-R, STAT3, StAR, and testicular steroidogenic enzymes (3β-HSD, P450c17, and P450scc). Moreover, RNA-seq analyses of testis during the different periods showed that a total of 4209 genes were differentially expressed genes (DEGs); further analysis revealed that DEGs related with the Jak/STAT pathways and reproduction were altered. Taken together, the results suggested that the leptin regulated testicular function through the Jak/STAT pathways and testicular steroidogenic factor expressions.

Mass Spectrometry Imaging of Lipids in the Scent Glands of Muskrat (Ondatra zibethicus) in Different Reproductive Statuses

As a typical seasonal breeding animal, male muskrats have a pair of scent glands that can emit musky odor substances to attract females during the breeding period. The present study aimed to visualize the differences in the distribution of lipids in the scent glands of muskrats during their different reproductive statuses by imaging mass spectrometry and quantitative real-time PCR (qRT-PCR). The results revealed remarkable differences in the expression and spatial distribution of lipids detected in the scent glands of muskrats during the different reproductive statuses. In addition, the expression levels of lipid molecules PC (32:0) and LysoPC (16:0) were found to be significantly higher in the breeding season than in the non-breeding season. Moreover, the mRNA expression levels of lipid synthesis enzyme Pemt and Pla2g4b were higher in the breeding season than in the non-breeding season, and there were positive correlations between the expression intensities of lipid molecules and the expression levels of Pemt and Pla2g4b. The present study investigates the changes and distribution of the endogenous lipid in the scent glands of muskrats and elucidates that the seasonal changes in the lipid metabolism may affect the functions of the scent glands in muskrats.

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.

Characteristics of steroidogenesis-related factors in the musk gland of Chinese forest musk deer (Moschus berezovskii)

Musk secreted by Chinese forest musk deer (FMD; Moschus berezovskii) is a highly valuable ingredient in the fields of perfumery and medicine, and the main factor affecting the production of musk is the androgen level of male FMD. To clarify whether the musk gland of FMD can synthesize androgen, we compared and analyzed the expression patterns of steroid hormone biosynthesis-related genes in the musk gland and testis of FMD by RNA-seq and RT-qPCR. We obtained 33,308 and 38,602 unigenes from the musk gland and testis, respectively, and 26,780 co-expressed unigenes. Analysis of co-expressed genes revealed that 12,647 genes were annotated to 11,484 Gene Ontology terms and 10,941 genes were annotated to 6120 pathways, including several pathways important in metabolic and synthetic activity. Next, 21 steroid hormone synthesis-related genes were screened from the transcriptome of the musk gland of 4-month-old FMD. The expression levels of three key genes of steroid hormone biosynthesis (CYP11A1, CYP17A1, and HSD3B) in the musk gland differed from their expression levels in the testis based on RT-qPCR. Furthermore, immunohistochemistry indicated that CYP11A1, CYP17A1, and HSD3B were localized in the glandular tubular columnar cells of the musk gland. These results suggested that the musk gland of male FMD has the potential to locally synthesize steroid hormone and thus plays a critically important role in musk secretion.

Seasonal expressions of SF-1, StAR and P450scc in the scent glands of the muskrats (Ondatra zibethicus)

The steroidogenesis occurs in specific cells and tissues in the mammals which begins with the transfer and intracellular processing of cholesterol converted to pregnenolone. This study investigated the gene and protein expression levels of steroidogenic factor 1 (SF-1), steroidogenic acute regulatory protein (StAR) and cytochrome P450 cholesterol side-chain cleavage enzyme (P450scc) in the scent glands of the muskrats during the breeding and non-breeding seasons. The immunohistochemical localizations of StAR and P450scc were identified in the glandular cells and epithelial cells while SF-1 was only expressed in glandular cells during the breeding and non-breeding seasons. The gene and protein expression levels of SF-1, StAR and P450scc in the scent glands were remarkedly higher in the breeding season than those of the non-breeding season. The interaction of micro RNAs (miRNAs) and transcriptome results showed that miR-762 and miR-4454 might be the genes encoding (Nr5a1, Star and Cyp11a1) in key biological processes. Taken together, these results suggested that the scent glands of the muskrats potentially owned ability to synthesize steroid hormones de novo, and the steroid hormones might affect the scent glandular functions of the muskrats during the breeding and non-breeding seasons.

Consequences of steroid-5α-reductase deficiency and inhibition in vertebrates

In 1974, a lack of 5α-dihydrotestosterone (5α-DHT), the most potent androgen across species except for fish, was shown to be the origin of a type of pseudohermaphrodism in which boys have female-like external genitalia. This human intersex condition is linked to a mutation in the steroid-5α-reductase type 2 (SRD5α2) gene, which usually produces an important enzyme capable of reducing the Δ⁴-ene of steroid C-19 and C-21 into a 5α-stereoisomer. Seeing the potential of SRD5α2 as a target for androgen synthesis, pharmaceutical companies developed 5α-reductase inhibitors (5ARIs), such as finasteride (FIN) and dutasteride (DUT) to target SRD5α2 in benign prostatic hyperplasia and androgenic alopecia. In addition to human treatment, the development of 5ARIs also enabled further research of SRD5α functions. Therefore, this review details the morphological, physiological, and molecular effects of the lack of SRD5α activity induced by both SRD5α mutations and inhibitor exposures across species. More specifically, data highlights 1) the role of 5α-DHT in the development of male secondary sexual organs in vertebrates and sex determination in non-mammalian vertebrates, 2) the role of SRD5α1 in the synthesis of the neurosteroid allopregnanolone (ALLO) and 5α-androstane-3α,17β-diol (3α-diol), which are involved in anxiety and sexual behavior, respectively, and 3) the role of SRD5α3 in N-glycosylation. This review also features the lesser known functions of SRD5αs in steroid degradation in the uterus during pregnancy and glucocorticoid clearance in the liver. Additionally, the review describes the regulation of SRD5αs by the receptors of androgens, progesterone, estrogen, and thyroid hormones, as well as their differential DNA methylation. Factors known to be involved in their differential methylation are age, inflammation, and mental stimulation. Overall, this review helps shed light on the various essential functions of SRD5αs across species.

Seasonal expressions of androgen receptor, estrogen receptors, 5α-reductases and P450arom in the epididymis of the male muskrat (Ondatra zibethicus)

The steroid hormones not only exert various endocrine functions but also act as the autocrine or paracrine factors in different tissues of mammals. In the present study, the seasonal expressions of androgen receptor (AR), estrogen receptors alpha and beta (ERα and ERβ), aromatase cytochrome P450 (P450arom) and 5α-reductase 1, 2 were investigated in the epididymis of the muskrat. HE staining showed enlarged lumen and abundant sperm in the breeding season while reduced lumen with no sperm in the non-breeding season. The staining of AR was presented in nuclei of epithelial cells of the epididymis in both seasons. The immunostaining of ERα was localized in both nuclei and cytoplasm of epithelial cells of the epididymis during the breeding season, while the weak staining of ERα was only in the nuclei of epithelial cells during the non-breeding season. In contrast, ERβ signal was negative in the epididymis of the muskrat in both seasons. The positive signals for P450arom and 5α-reductase 1, 2 were found in the cytoplasm of epithelial and smooth muscle cells during both seasons. Moreover, the protein and mRNA expression levels of AR, ERα, P450arom and 5α-reductase 1, 2 were significantly higher in the epididymis during the breeding season than those of the non-breeding season, and the expression level of 5α-reductase 1 was higher when compared with 5α-reductase 2. In addition, the levels of testosterone (T) and dihydrotestosterone (DHT) in the epididymis and serum were remarkably higher during the breeding season. Taken together, these findings suggested androgen and estrogen might play an important endocrine or autocrine/paracrine role to regulate the epididymal functions of the muskrat.

Seasonal expressions of growth hormone receptor, insulin-like growth factor 1 and insulin-like growth factor 1 receptor in the scented glands of the muskrats (Ondatra zibethicus)

The growth hormone (GH)/insulin-like growth factor-1 (IGF-1) system plays an important role in regulating the cellular growth and organ development. The present study investigated the seasonal expressions of growth hormone receptor (GHR), IGF-1 and insulin-like growth factor 1 receptor (IGF-1R) in the scented glands of the muskrats. Morphological changes in the scented glands of the muskrats were observed significantly between the breeding and non-breeding seasons. Immunohistochemically, the expressions of GH, GHR, IGF-1 and IGF-1R were found in glandular cells and epithelial cells of the scented glands in both seasons. The protein and mRNA expression levels of GHR, IGF-1 and IGF-1R in the scented glands during the breeding season were noticeably higher than those of the non-breeding season. In parallel, the levels of GH and IGF-1 in the sera and scented glands were remarkably higher during the breeding season. In addition, small RNA sequencing showed that the predicted targets of the significantly changed hsa-miR-5100 and mmu-miR-6937-5p might regulate the expressions of Ghr, Igf-1 or Igf-1r. These results suggested that the morphological changes in the scented glands of the muskrats during the different seasons might be related to the expression levels of GHR, IGF-1 and IGF-1R. Meanwhile, GHR/IGF-1 system might regulate the scented glandular functions via endocrine or autocrine/paracrine manners.

Seasonal expressions of prolactin, prolactin receptor and STAT5 in the scented glands of the male muskrats (Ondatra zibethicus)

Prolactin (PRL) production in mammals has been demonstrated in extrapituitary gland, which can activate autocrine/ paracrine signaling pathways to regulate physiological activity. In the current study, we characterized the gene expression profiles of PRL, prolactin receptor (PRLR) and signal transducers and activators of transcription 5 (STAT5) in the scented glandular tissues of the muskrats, to further elucidate the relationship between PRL and the scented glandular functions of the muskrats. The weight and volume of the scented glands in the breeding season were significantly higher than those of the non-breeding season. Immunohistochemical data showed that PRL, PRLR and STAT5/phospho-STAT5 (pSTAT5) were found in the glandular and epithelial cells of the scented glands in both seasons. Furthermore, we found that PRL, PRLR and STAT5 had higher immunoreactivities in the scented glands during the breeding season when compared to those of the non-breeding season. In parallel, the gene expressions of PRL, PRLR and STAT5 were significantly higher in the scented glands during the breeding season than those of the non-breeding season. The concentrations of PRL in scented glandular tissues and sera were measured by enzymelinked immunosorbent assay (ELISA), and their levels were both notably higher in the breeding season than those of the nonbreeding season. These findings suggested that the scented glands of the muskrats were capable of extrapituitary synthesis of PRL, which might attribute PRL a specific function to an endocrine or autocrine/paracrine mediator.