Molecular Characterization, Tissue Distribution, and Expression Profiling of the CTSD Gene during Goose Ovarian Follicle Development

Cathepsin D (CTSD) is known to be crucial for the degradation and utilization of yolk precursors in ovarian follicles. However, little is known about its expression profiles and physiological actions in avian ovarian cells. In this study, the intact coding sequence of the CTSD gene in geese was cloned for the first time, with a length of 1197 bp. It encoded a polypeptide of 398 amino acids (AA) consisting of a signal peptide and two conserved functional domains (i.e., A1_Propeptide and Cathepsin_D2). The AA sequence of goose CTSD had > 96% similarities with the homologs of turkeys, chickens, and ducks. Results from real-time PCR showed that goose CTSD mRNA was present in all tissues examined, with higher levels in the adrenal gland, liver, heart, and reproductive organs. Furthermore, levels of CTSD mRNA were much higher in goose granulosa layers than in the theca layers in any follicular category. Significantly, its expression remained almost unchanged in the theca layers throughout follicle development, while it increased gradually in the granulosa layers from 2-4 mm to F5 follicles but declined there after. These results suggested that CTSD may regulate goose ovarian follicle development through its actions on both the degradation and absorption of yolk precursors and granulosa cell apoptosis.