Molecular characterization of the major yolk protein of the Japanese common sea cucumber (Apostichopus japonicus) and its expression profile during ovarian development

The most abundant protein in the coelomic fluid of the Japanese common sea cucumber (Apostichopus japonicus) was purified through two steps of liquid chromatography. Subsequent peptide sequencing and cDNA cloning demonstrated that the purified fraction contained two similar but distinct proteins. Deduced amino acid sequences of these proteins revealed about 30% identity with those of sea urchin major yolk protein (MYP) and therefore they were designated AjMYP1 and AjMYP2. The full-length cDNAs for AjMYP1 and AjMYP2 consisted of 4600 and 4420 bp, with predicted protein lengths of 1365 and 1345 amino acid residues, respectively. RT-PCR detected transcripts for both types of AjMYPs in all the tissues and organs examined. The transcript levels of both AjMYPs in the ovary were apparently elevated at late stages of ovarian development whereas the MYP content of the ovary examined by SDS-PAGE remained stable throughout ovarian development.