Sequence Analysis And Expression Profiling Of The Goose(Anser Cygnoide), Two Very Low Density Lipoprotein Receptors During Follicle Development

In this study, we analyzed the cDNA sequences of the two goose VLDLR gene isoforms and investigated their expression patterns during follicle development to provide new information on clarifying the mechanism controlling yolk lipid deposition in birds. Taking the maternal line of TianFu goose as the model, the full length cDNAs encoding two VLDLR subtypes were sequenced from the goose ovary, which displayed greater than89.5%identity with VLDLR sequences of other birds. The larger one (type I VLDLR) contains five conserved domains resembling other members of low density lipoprotein receptor (LDLR) superfamily, including the ligand binding domain (LBD), epidermal growth factor (EGF) precursor homology domain, O-linked sugar domain, transmembrane domain and extracellular containing NPxY motif domain from the N to C terminal, while the shorter one (type II VLDLR) lacks the O-linked sugar domain.The mRNA tissue distribution and expression profiling of geese two VLDLR subtypes during follicle development were analyzed by semi-quantitative RT-PCR. The results showed that two variants were differentially expressed in all tested tissues with higher expression of type Ⅱ VLDLR in reproduction-related organs (such as pituitary, ovary, oviduct, etc). Throughout follicular development, type I VLDLR was low-expressed in theca cells and undetectable in granulosa cells, where higher mRNA levels of type Ⅱ VLDLR were found. Expression of type Ⅱ VLDLR in both theca and granulosa cells decreased as follicular diameter increased. In addition, we also investigated the levels of yolk triglycerides, total cholesterol and very low density lipoprotein with growing follicular diameter and analyzed the correlation between expression of two VLDLR subtypes and yolk lipid components. The results showed that: yolk TG and TC contents showed a growing trend with the growth of follicle diameter, while yolk VLDL contents showed a reverse trend. The yolk VLDL content in small follicles were significantly higher than that in large follicles (p<0.05). The correlation analysis found that expression of type Ⅱ VLDLR in both the theca and granulosa cells showed a significant correlation with yolk lipid components (p<0.01), indicating that type Ⅱ VLDLR may play a major role in the process of yolk lipid deposition.We also revealed the effects of cholesterol,25-hydroxycholesterol and mevinolin (HMG-CoA reductase inhibitors) on transcripts of VLDLR in both prehierarchical and preovulatory granulosa cells. The results showed that type I VLDLR was devoid in all cultured cells, however, steroids treatment contributed to different expression patterns of type Ⅱ VLDLR between prehierarchical and preovulatory granulosa cells, indicating its possible role in promoting granulosa cell differentiation by affecting the steroid biosynthesis. These findings suggest that type Ⅱ VLDLR is ovary-specific receptor that mediates the lipoproteins into the follicles, and provide new evidence about the influence of steroids in modulating expression of VLDLR in ovarian cells.