[Isolation and expression of novel expressed sequence tags (ESTs) from ovarian follicles of Shaoxing ducks]

Three expressed sequence tags ( ESTs), SXDF0201 (271 bp), SXDF0202 (200 bp) and SXDF0203 (173 bp), were isolated from ovarian follicles of Shaoxing ducks by using silver staining mRNA differential display. GenBank/BLAST analysis revealed that SXDF0201 was not homologous to any of the published sequences from all species, indicating that it was a novel EST and was then registered in GenBank (GenBank Accession No.: CB072629), while SXDF0202 and SXDF0203 were found to be highly homologous to seven known chicken ESTs and chicken mRNA for gizzard smooth muscle myosin heavy chain. 5'-RACE was employed to extend the SXDF0201 to 544 bp which was confirmed as novel in BLAST search. The temporal and spatial expression of SXDF0201 and SXDF0202 were also investigated with semi-quantitative RT-PCR. The result showed that: both SXDF0201 and SXDF0202 were found to be expressed in hypothalamus, pituitary, muscle, liver, and fat tissues of Shaoxing ducks; SXDF0201 was expressed significantly higher in ovaries of 30-day-old Shaoxing ducks compared with that of 60-day-old (P < 0.05) and 90-day-old (P = 0.015), but the expression of SXDF0202 showed no difference throughout the ovarian development; granulose layers expressed higher SXDF0201 than theca layers in almost all hierarchical follicles, the expression of SXDF0202 in granulose layers increased along with follicular maturation (P < 0.01) from Fw to F3 follicles, but decreased dramatically to the lowest in F1 follicles (P < 0.01). In theca layers, the highest expression of SXDF0202 was found in Fw follicles (P < 0.01).