Evolution of the concepts of vitellogenesis in Polychaete Annelids

Summary In polychaete annelids, two types of vitellogenesis have been described: a heterosynthetic mechanism (in a number of different of worms) and an autosynthetic process (other including Nereis). Recent biochemical results suggest that the heterosynthetic mechanism is more general than previously thought. In Nereis, the vitellogenin (the precursor) is synthesized in coelomocytes and after transfer through coelomic fluid incorporated into oocytes. In germinal cells, a conversion process, involving proteolytic cleavages of vitellogenin, produces mature vitellins which are accumulated in yolk granules. The neurohormones identified so far are not essential for vitellogenin synthesis. It is possible that these neurohormones regutate enzymatic activities in the oocytes.