CHAN, S.-M.; GU, P.-L.: Molecular characterization of a cDNA encoding for a shrimp Cellular Retinoic Acid/Retinol Binding Protein

Members of the cellular retinoic acid binding protein (CRABP) family are small proteins involved in the metabolic pathways of retinoic acid (RA). Although there is report describing the cloning of a retinoic-X receptor, no report describes the presence of RA in crustacean. To determine whether RA is also involved in the regulation of development and whether CRABP is also involved in the metabolism of RA in crustacean, we attempt to clone the CRABP cDNAs from the shrimp using a combination of RT-PCR and library screening approach. Several identical cDNA clones encoding the putative MeCRABP were isolated. As confirmed by DNA sequence determination and RNA Northern blot analysis, the size of the CRABP mRNA is 0.9 kb. The cDNA is estimated to encode for a protein of 14 kDa. The size is close to that of the retinoic/fatty acid binding protein reported in the vertebrate and invertebrate. MeCRABP is expressed abundantly in the ovary and moderately in the eyestalk. Other tissues such as the muscles and testis also express these genes. Recombinant protein for the shrimp CRABP was produced in a pRSET bacteria expression system. Purified fusion protein was used to immunize rabbit to raise antibody. The fusion protein binds to both retinoic acid (RA) and retinol (RO) with similar affinity. Anti-rCRABP recognises cells of the eyestalk as well as maturing oocytes of shrimp contain CRABP. Supported by HKU CRCG.