Construction of SMART cDNA Library of Sheep Ovary and Identification of Candidate Gene by Homologous Cloning

The cDNA library of an ovary from Small Tail Han sheep before estrus was constructed by switching mechanism at 5 end of RNA transcript (SMART) approach. This library had a plaque liter of 1 × 109 pfu mL−1 and a 96% recombinant ratio of which the fragment length of inserted average cDNA sequences was 1.0 kb. Based on bioinformatics analysis of the sequences, we obtained 338 expressed sequence tags (ESTs) from 380 cDNA clones which indicated 191 contigs. These contigs consist of 89 unmatched ESTs, 9 homologous known genes in sheep, and 93 homologous sequences in species of mouse, bovine, and human beings, including 19 sequences expressed in the ovary or follicle and 14 unknown sequences. Several candidate genes associated with sheep reproduction trait such as epidermal growth factor (EGF), estrogen receptor (ESR), Inhibin, follicle stimulating hormone receptor (FSHR), prostaglandin (PG), and transforming growth factor-β (TGF-β) were identified and the homologous were cloned from this library, which will contribute to compile expression profiles and find the major genes of prolificacy of Small Tail Han sheep.