Screening Of Differentially Expressed Genes In Ovary And Endocrine Study On Year-round Estrus In Sheep

Sheep are seasonal breeders. The breeding season begins at the end of summer or at the beginningof spring. This seasonal estrus limited the ewe productivity and leads to the seasonal lambing, so theprime lamb provided has the seasonal variations depend on the sheep seasonal estrus. Most of sheep areseasonal breeders in China, which limited the efficient and sustainable development of the sheepindustry. In order to change the seasonal estrus at the genetic level, the endocrine basis and the keygenes related to seasonal estrus should be understood firstly.The objective of this study is to analyze the seasonal changes of year-round and seasonal estrussheep.Melatonin, E2, P4, FSH and LH concentration in serum and the gene expression pattern of ovaryin different reproductive status were determined. Our results could provide theoretical basis forregulating the seasonal reproduction in sheep.Blood samples were collected from five Small Tail Han sheep and five Tan sheep in spring,summer, autumn and winter, respectively. The melatonin, E2, P4, FSH and LH in serum were measuredby radioimmunoassay. Ovaries were collected from Small Tail Han sheep in the different estrous periodincluding the end of dioestrus, proestrus and estrus, and Tan sheep during the anestrous in spring. TheRNA-Seq was used to screen the differently expressed genes in ovary. Our results were listed as follows:(1) Secretion pattern of Serum MLT. MLT level at night was significantly higher (P<0.05) than that inthe day. The increase and decrease of the speed was fastand normally completed in1hours.Then theMLT remained at either a high level or low level until sunrise or sunset. The MLT level of Small TailHan sheep showed no significant changes around the year. However, it was different in Tan sheep. MLTlevel in the autumnal equinox and winter solstice were significantly higher (P<0.05) than that in springequinox and summer solstice. The day and night MLT levels of Small Tail Han sheep showed nosignificant changes during four seasons. However, the night MLT level of Tan sheep showedsignificantly increased (P<0.05) in autum and winter. The results indicated that the night MLT levelplays an important role in seasonal reproduction regulation in sheep.(2) Secretion pattern of Serum reproductive hormone. The results showed that the concentrations ofthese four hormones in Small Tail Han sheep had no significant changes around the year. However, itwas different in Tan sheep. P4, FSH and LH concentration in estrous season were significantly higher(P<0.05) than those in anestrous season. According to the analysis between two breeds, E2level has nosignificant difference（P>0.05）around the year. The serum P4and FSH concentration in Small TailHan sheep were significantly higher (P<0.05) than in Tan sheep during spring and summer. The LHlevel in Small Tail Han sheep was higher than in Tan sheep, however, has no significantdifference(P>0.05) except in winter. These results indicated that a certain level of E2and P4wereneeded for sheep year-round estrous, and high level of FSH and LH were necessary for year-roundestrus or polyembryony in sheep.(3) RNA-Seq was used for determining the gene expression pattern in the different reproductive status.According to the hierachical clustering results of differentially expressed genes from the different reprodctive status. The results showed that the genes of anestrus and diestrus, proestrus and estrus wereclustered together firstly. These indicated that sheep in anestrus and diestrus, proestrus and estrus had asimilar gene expression pattern.(4) RNA-Seq analysis of differentially expressed genes generated a list of767genes with396as knownand371as unknown, and with702as up-regulated and65as down-regulated. The most significantlyoverrepresented GO terms are related to binding, organell, cell, cell part, cell process and metabolicprocess, etc. Moreover, KEGG pathway analysis revealed that many pathways such as TGFβ signalingpathway, Steriod biosynthesis, insulin signaling pathway, Notch signaling pathway, Flavone andflavonol biosynthesis as well as Progesterone-mediated oocyte maturation, etc. had been regulatedremarkably at the different reproductive status of sheep ovary. And FSTL3, SMAD1, SMAD4andTGFBRII and BAD gene may the important candidate gene for year-round estrus regulation.