CHICKEN OOCYTE GROWTH IS MEDIATED BY AN 8 LIGAND-BINDING REPEAT MEMBER OF THE LDL RECEPTOR FAMILY

Deposition of the yolk mass components of chicken oocytes, very low de nsity lipoprotein (VLDL) and vitellogenin (VTG), is mediated by a 95 k Da plasma membrane protein, termed VLD/NTG receptor (VLDL/VTGR). Molec ular characterization of the VLDL/VTGR revealed that it is a member of the LDLR gene superfamily, and harbours eight complement-type, cystei ne-rich ligand binding repeats at the N-terminus. This ligand binding domain structure is the hallmark of the recently discovered mammalian so-called VLDLRs, whose true physiological function be elucidated. Nor thern blot analysis that this receptor is expressed almost exclusively in oocytes, with very much lower levels of hybridizing transcripts pr esent in heart and skeletal muscle. Heterologous expression of the clo ned receptor demonstrated its ability to bind both VLDL and VTG. The r eceptor gene is located on the avian sex chromesome Z, in agreement wi th the sex linkage of a single-gene defect in animals that fail to rep roduce because of the lack of expression of functional VLDL/VTGR. In s itu hybridization analysis of oocytes suggested that VLDL/VTGR mRNA ma y relocalize during oocyte growth. Thus, the current study has identif ied and characterized the first non-mammalian VLDLR. Its key role in a vian reproduction and extremely high evolutionary conservation shed ne w light on VLDLR function in mammals, which also express the gene in o varies.