Molecular cloning and expression of FGF2 gene in pre-implantation developmental stages of in vitro-produced sheep embryos

Early embryonic mortality is one of the main sources of reproductive loss in domestic ruminants including sheep. Fibroblast growth factor-2 (FGF-2) is a member of FGFs family that mediates trophoblast activities and regulates embryonic development in various species. In this study, we have cloned, characterized sheep FGF2 cDNA (KU316368) and studied the expression in sheep embryos. Ovaries of non-pregnant sheep were collected from local abattoir and matured in culture medium at 38.5ºC, 5% CO₂ , 95% humidity for 22-24 hr. The matured oocytes were inseminated with capacitated spermatozoa in Brackett and Oliphant medium and resulted embryos were cultured in CO₂ incubator for 6-7 days to complete the developmental stages from two cells to blastocyst stage. Total RNA was extracted from immature oocytes (n = 100), mature oocytes (n = 100) and different stages of embryos such as 2 cell (n = 50), 4 cell (n = 25), 8 cell (n = 12), 16 cell (n = 6), morula (n = 5) and blastocyst (n = 3). The total RNA isolated from the oocytes and embryos was reverse transcribed and subjected to real-time polymerase chain reaction using sequence-specific primers and SYBR green as the DNA dye. On sequence analysis, the nucleotide sequence of sheep FGF2 exhibited highest sequence similarity with cattle (100%) and least with rat and mouse (69.2%). At the deduced amino acid level, a highest degree of similarity was noticed with cattle, buffalo, goat, pig, camel and horse (100%) and lowest degree of identity with rat, human and mouse (98.2%). The FGF2 mRNA expression was higher in immature and mature oocytes and gradually decreases from 2-cell stage of embryo to the blastocyst stage. More over a significant differences in FGF2 mRNA expression (p < .05) were observed between immature oocytes and all pre-implantation stages of embryo. It can be concluded that FGF-2 plays a significant role in pre-implantation and early development of embryos in sheep.