Ovarian expression and localization of a low-density lipoprotein receptor related protein 13 (Lrp13) in orange-spotted grouper (Epinephelus coioides)

Abstract

Low-density lipoprotein receptor (LDLR) superfamily is an ancient gene family composed of different genes encoding membrane receptors involved in ligand binding and endocytosis. These receptors typically consist of class A ligand-binding repeats (LBRs), epidermal growth factor precursor-like (EGF) domain, class b YWXD motifs, transmembrane (TM) domain, and cytoplasmic (CP) domain. Low-density lipoprotein receptor related protein 13 (Lrp13), a vitellogenin receptor with a unique domain structure, belonging to the LDLR superfamily, would play an important role in vitellogenesis in teleosts. In this study, the full-length cDNA of Ec-lrp13 was isolated from the ovary of orange-spotted grouper (Epinephelus coioides), an economically important aquaculture species in China. The open reading frame (ORF) of Ec-lrp13 is 3831 bp in length, encoding 1276 amino acids. The Ec-Lrp13 includes several typical domains of the LDLR superfamily and contains the specific structure of the Lrp13 protein. Ec-lrp13 is predominantly expressed in ovary. During ovarian development, Ec-lrp13 was highly expressed in stage II and III ovaries but its mRNA level was significantly decreased in stage IV ovary. In situ hybridization (ISH) analysis revealed that Ec-lrp13 mRNA signals were obviously observed in the ooplasm of PG and EPV oocytes, but decreased in the LPV oocytes, and weakly found in the VG oocytes. Immunohistochemistry (IHC) detection showed that Ec-Lrp13 protein signals were only observed in the LPV and VG oocytes. Our data provides preliminary evidence that Lrp13 may be involved in the Vtg uptake during ovarian development of orange-spotted grouper.