Spatiotemporal expression pattern of gonad-stimulating substance-like peptide of the sea cucumber, Apostichopus japonicus.

The spatiotemporal expression pattern of gonad-stimulating substance-like peptide-containing polypeptide (GSSLP) in the sea cucumber Apostichopus japonicus was examined using immunochemistry. The GSSLP was detected in the gonads from shortly before the empirical breeding season (May and June) to July. On the basis of immunoblotting analysis, GSSLP showed considerable polymorphism among the organs examined in this study, particularly in the gonads, in which the polymorphism was associated with N-glycosylation and the formation of intra-molecular disulfide bonds. In the ovary, GSSLP was expressed from March to June and corresponded to two bands at 113 and 100 kDa under reducing conditions. In July, only the larger band weakly remained. In testis, GSSLP was detected first in April as two bands of 245 and 190 kDa under reducing conditions. The number of bands increased to five in June but decreased to three smeared bands in July. In the radial nerve and circumoral nerve ring, GSSLP corresponded to a single peptide of 170 kDa with little N-glycosylation and its expression level hardly changed throughout a year with no correlation with the breeding season. GSSLP was detected mainly in the morula cells in all the organs examined. In addition, GSSLP was detected in the follicle cells of the ovary and, for a brief period, in the jelly space, but never in the ooplasm. In testis, the morula cells were localized close to the invaginated inner epithelium, but never in the male gametes. In July animals, gonadal morula cells were rarely observed.