Expression and role of melatonin membrane receptors in the hypothalamic-pituitary-testicular axis of Tibetan sheep in a plateau pastoral area

Abstract

MTNR1A and MTNR1B, two high-affinity MT membrane receptors found in mammals, mediate the activity of MT on the HPGA to regulate animal reproduction. Nevertheless, the expression patterns and function of the MTNR1A and MTNR1B genes in the HPTA of seasonal estrus sheep and perennial estrus sheep have not been elucidated. We studied the expression of MTNR1A and MTNR1B in the hypothalamic-pituitary-testicular axis (HPTA) of Tibetan sheep at different reproductive stages using histochemistry, enzyme linked immunosorbent assay (ELSIA), scanning electron microscopy, transmission electron microscopy, quantitative Real-time PCR (qRT-PCR), and Western blot (WB), and analyzed the relationship between their expression and reproductive hormone receptors. We also compared relevant characteristics between seasonal Tibetan sheep and non-seasonal Small Tail Han sheep in the same pastoral area. The results showed that MTNR1A and MTNR1B were expressed in all tissues of the Tibetan sheep HPTA, and both were co-expressed in the cytoplasm of epididymis basal and halo cells located at common sites of the epididymis basement membrane, forming an immune barrier. The qRT-PCR analysis showed that not only MTNR1A but also N-acetyltransferase (AANAT), hydroxyindole-oxygen- methyltransferase (HIOMT), androgen receptor (AR), and estrogen receptor α (ERα) mRNA expression was significantly upregulated in the testis and epididymis of Tibetan sheep during the breeding season, whereas no clear upregulation of these genes was observed in the tissues of Small Tail Han sheep. MTNR1A and MTNR1B are important regulators of the HPTA in sheep. MTNR1A mediates seasonal estrus regulation in Tibetan sheep. Both MTNR1A and MTNR1B may play important roles in formation of the blood-epididymal barrier. The results of this study should help advance research on the mechanism of reproductive regulation of the HPTA in male animals and provide reference data for improving the reproductive rate of seasonal breeding animals.

Cellular mechanism of gain-of-function mutation I173M in sheep MC4R gene identified in year-round and seasonal estrus breeds through whole-genome resequencing

“…This includes genes such as Clock, BMAL1, Per1, Per2, Cry1 and Cry2, which are believed to potentially affect seasonal estrus 10,11 . Transcriptomic sequencing has been employed to analyze tissues, for instance, the hypothalamus, pituitary, and ovary tissues of seasonal and non-seasonal reproductive sheep [12][13][14] , revealing candidate genes such as MTNR1A 15 , GNAQ 16 and SEMA7A 13 linked to sheep estrus. These genes may play crucial roles in regulating the seasonal reproductive processes in sheep, offering valuable clues for unraveling the mechanisms behind seasonal reproduction.…”

“…In sheep, breeds such as Hu sheep, Large Tail Han sheep, and Cele black exhibit year-round reproductive behaviors [17][18][19] . In contrast, Tibetan sheep and Tan sheep develop their gonads at speci c times of the year and demonstrate seasonal reproductive behaviors 5,15 . Therefore, using both year-round and seasonal estrus sheep breeds as models can facilitate a more comprehensive investigation into the molecular mechanisms underlying seasonal reproduction in sheep.…”