Seasonal Expression of Prolactin Receptor in the Scented Gland of Male Muskrat (Ondatra zibethicus)

Abstract

Prolactin (PRL) has numerous actions in mammalian biological systems including mammary development and biological processes. The aim of this study was to investigate the seasonal changes of prolactin receptor (PRLR) expression in the scented gland of muskrat during the breeding and nonbreeding seasons. Histologically, glandular cells, interstitial cells and excretory tubules were identified in the scented glands in both seasons, whereas epithelial cells were sparse in the nonbreeding season. PRLR was observed in glandular cells of scented glands during the breeding and nonbreeding seasons with stronger immunostaining during the breeding season. Consistent with the immunohistochemical results, both the mean of protein and mRNA levels of PRLR were higher in the scented glands of the breeding season, and relatively lower level in the nonbreeding season. In addition, differential seasonal changes were also detected in the expression profile of microRNAs (miRNAs) in the scented gland of muskrat. Besides, plasma PRL concentration was remarkably higher in the breeding season than that in the nonbreeding season. These results suggested that muskrat scented gland was the direct target organ of PRL, and stronger expression of PRLR in scented glands during the breeding season indicated that PRL may directly regulate scented glandular function of the muskrats.

Figure 1. Histological structure of the muskrat scented glands and testes, and immunolocalization for PRLR in scented glands of the muskrat.

(a) Hematoxylin-eosin (HE) staining of scented gland during the breeding season. (b) HE staining of scented gland during the nonbreeding season. (c) HE staining of testis during the nonbreeding season. (d) HE staining of testis during the breeding season. (e) Immunolocalization for PRLR in scented glands during the breeding season. (f) Immunolocalization for PRLR in scented glands during the nonbreeding season. (g) PRLR detected in the mammary of muskrat was used as a positive control. (e’–f’) No signal was detected in negative control sections in which the primary antibody was pre-absorbed by a respective antigen. (h) Negative control sections were also treated with normal rabbit serum instead of primary antisera. GC, glandular cells; EC, epithelial cells; IC, interstitial cells; ED, excretory ducts; LC, Leydig cell; Spg, spermatogonium; pSpc, primary spermatocyte; rSpd, round spermatid; eSpd, elongate spermatid. Scale bars represent 50 μm.

Figure 2. Protein and mRNA expression of PRLR in the scented gland and plasma level profile of prolactin.

The seasonal profiles of protein (a) and mRNA (b) expression of PRLR in the scented glands of the muskrat. Each bar represents the means ± standard deviation of 6 muskrats per group. Means within the two columns are significantly different from each other (p < 0.05). (c) The seasonal profiles of serum prolactin concentration. Bars represent means ± standard deviation for independent experiments. Asterisks denote statistically significant values (p < 0.01).

Figure 3. Sequence length distribution and annotation of unique small RNA (sRNA).

(a) Sequence length distribution of unique sRNA for SGB1; (b) Sequence length distribution of unique sRNA for SGNB2; (c) Annotation of unique sRNA for SGB1; (d) Annotation of unique sRNA for SGNB2.