Molecular characterization, tissue distribution, and expression of two ovarian Dicer isoforms during follicle...

Dicer plays a key role in the biogenesis of microRNAs and small interfering RNAs, which control the coordinated expression of multiple of genes during follicle development. In this study, the cDNAs encoding two Dicer isoforms (gDicer-a and gDicer-b, respectively) were isolated and cloned from goose ovary using RT-PCR. This is the first time a new Dicer splice variant has been characterized at the molecular level in vertebrates. Sequence analysis indicated that both of the two isoforms consist of seven conserved functional domains, where gDicer-b lacks a linker sequence between DEAD box and helicase C domain composed of 158 amino acids. Each domain of gDicer-a/gDicer-b showed higher than 89.5% identity to corresponding domain of Dicers from chicken, human, and mouse. The ubiquity of transcripts of gDicer-a/gDicer-b was found in all tested tissues by real time PCR with the pituitary, oviduct, and hypothalamus being the predominant site of expression of gDicer-a. A similar expression profile of the gDicer-a/gDicer-b mRNAs was found during follicle development. The abrupt changes in transcripts of gDicer in 2-4mm, 9-10mm, F5, and F1 follicles support its participation in the process of follicle recruitment, selection, dominance, and ovulation. However, high mRNA levels of gDicer-b and caspase-3 were detectable in atretic and post-ovulatory follicles, where expression of gDicer-a was considerably low. These findings suggest that gDicer is required for follicle development, and structural differences in the helicase domain of two gDicer isoforms might contribute to their different roles in controlling granulosa cell apoptosis.