Generation and sequence characterization of a normalized cDNA library from swine ovarian follicles

Ovulation rate is a major factor determining litter size in swine and is, therefore, a trait of economic importance to the pork industry. The dynamics of follicle development, which in turn are dictated by a balance between follicle recruitment, maturation, selection, and atresia, are a major determining factor of ovulation rate. The role of several genes expressed in the ovaries during these processes has been described, but studies utilizing large-scale genomic approaches have yet to be conducted to examine gene expression in this tissue more globally. We have developed a normalized cDNA library from swine ovarian follicles in various stages of development, ranging from 2.0 to 10.0 mm in diameter, collected from gilts from divergent genetic lines selected for high and low ovulation rates, during the 7 initial days of the follicular phase of the estrous cycle. EST sequences were obtained from 5231 distinct clones derived from this library. In total, 3479 unique sequence clusters were obtained, of which 2661 singletons (76.5%) were observed. BLASTN searches with the primary sequences from the clusters obtained resulted in 1037 sequences not matching (E <1.0(-06) any of the sequences in the nt database (29.8% novelty rate). This resource will facilitate the use of cDNA microarrays in functional genomics studies aiming at unraveling the genetic and physiological mechanisms underlying follicle maturation and ovulation rate in swine.