Developmental and mRNA transcript relative abundance pattern of vitellogenin receptors, LR8-/Lrp13, during ovarian development in the large yellow croaker (Larimichthys crocea)

Abstract

For vitellogenin (Vtg) absorption to occur, there needs to binding of the glycolipophosphoproteins to the oocyte membrane in oviparous species, including teleosts. The cDNAs encoding homologous Vtg receptors (VgRs) LR8- and Lrp13 were cloned from ovaries of the large yellow croaker (Larimichthys crocea), an economically important species in Chinese aquaculture. The full-length Lc-lr8-/lrp13 cDNAs contained 4266/3760 base pairs (bp) and the deduced Lc-LR8-/Lrp13 proteins had 844/1218 amino acids, respectively. The VgRs comprised a ligand-binding domain, an epidermal growth factor precursor homology domain, YWXD motifs forming a β-propeller structure, and transmembrane and cytoplasmic domains. There was a marked relative abundance of Lc-lr8-/lrp13 transcripts in the tissues that were evaluated, with the largest abundance in the ovaries at Stage II of development. Furthermore, there was a lesser relative abundance of Lc-lr8-/lrp13 mRNA transcript during ovarian development (Stages II to IV). In situ hybridization technology was used to analyze decreasing relative abundance pattern of Lc-lr8-/lrp13 mRNA transcript during oogenesis in Stage II to IV of ovarian development. By combining mRNA relative abundance with morphological results, a model was developed to explain the reduction in Lc-lr8-/lrp13 mRNA transcript relative abundance during ovarian development. During the early developmental stages, transcription, translation, and differential accumulation of VgRs in previtellogenic and vitellogenic oocytes may occur and result in Vtg absorption in teleost oocytes. Overall, there is preliminary evidence indicating that at least two VgRs (Lc-LR8-/Lrp13) are present in the large yellow croaker and may be important for Vtg transport from the blood into the oocyte during ovarian development.