1 ǀ INTRODUCTION
Orientation and connection of trophectoderm of the migrated blastocyst to the luminal epithelial surface of the uterus is the critical period to harmonize the implantation cascade1. In this period, embryo mortality is most prevalent in all domestic ruminants2,3 and may be due to deficiencies attributed to immune functions, uterine functions, inappropriate conceptus development, and implantation4,5. Mononuclear cells of trophoectoderm of a preimplant embryo produces and release interferon tau (IFNT) between 11 to 24 day of pregnancy in ruminants5,6. This IFNT binds to the Type-1 IFN receptor (IFNR) located on luminal epithelial cells of endometrium7 and exerts its anti-luteolytic activity by different mechanisms8. Interferon tau induces and up-regulates the expression of several genes in the endometrium during pregnancy including 2’-5’-oligoadenylate synthetase-1 (OAS1)9,10,11.
The mammalian 2’-5’ oligoadenylate synthetases (2’-5’OASs) are enzymes that play a crucial role in mediating resistance to virus infection, control of cell growth, differentiation, and apoptosis12,13,14. It binds to double-stranded RNA and catalyzes the polymerization of ATP into 2’-5’-linked oligoadenylates which activate a constitutively expressed latent endonuclease, RNase L, to block viral replication and initiate apoptosis in some cell types. The mammalian OAS genes have undergone multiple gene duplication events resulting in three size classes of enzymes: small (40/46-kDa isoforms), intermediate (69/71-kDa isoforms), and large (100-kDa)15,16,17,18,19. The biological significance of these multiple OAS forms is unknown, but each has distinct subcellular locations and functional differences in activation requirements and catalytic parameters17,20,21,22. This protein is associated with different subcellular fractions such as mitochondrial, nuclear, and rough/smooth microsomal fractions.
OAS1 is the novel and most abundant gene expressed in cyclic and increased the level during early pregnancy in the endometrium of bovine and ovine, and is regulated by IFNT and progesterone9,11,23. Its level increases in the endometrium during early pregnancy and plays an important role in antiviral responses, control of cellular growth and differentiation for successful implantation, and pregnancy establishment in bovine and ovine9,10,11. In addition, intrauterine administration of IFNT along with progesterone stimulates OAS expression in the cyclic endometrium of the animals and/or in-vitro culture endometrial cells10,11. Even though the OAS1 is involved in uterine receptivity, implantation, and survivability of the embryo, it has not yet been studied in goats (Capra hircus) except one predicted sequence is available in NCBI (GenBank Acc. No. XM_005691488).
Goat (Capra hircus ) being a multi-functional animal and commonly known as the poor man’s cow, acts as a source of crop insurance and supplementary income along with nutritional security for lower, poor and marginal farmers in South Asian countries, especially in India24. The goat sector contributes 8.4 % to India’s livestock gross domestic product (GDP) through meat, milk, skin and manure25. Considering the important role of OAS1 in uterine receptivity and embryonic survival, in addition to its antiviral function, the present work was undertaken to amplify, sequence, characterize, analyze the integrative bioinformatics and elucidate expression patterns in goat endometrium.