Expression and translation of the egg-laying neuropeptide hormone genes during post-embryonic development of the pond snail Lymnaea stagnalis.

The neuroendocrine caudodorsal cells of Lymnaea stagnalis express two homologous genes, each encoding a polypeptide precursor. The precursors give rise to "cocktails" of neuropeptides that regulate egg-laying. The expression and translation of both egg-laying hormone genes during post-embryonic development were investigated by in situ hybridization and by electron-microscopic immunocytochemistry. Gene-II-specific transcripts and translation products were not found in caudodorsal cells in animals with shell heights smaller than 10 mm, in contrast to gene-I products that were present even at 3-mm shell height. The onset of expression of gene II coincides with the onset of release of products from the caudodorsal cells into the blood. Large electron-dense granules were found in caudodorsal cells of snails of all developmental stages investigated. These granules form part of the Golgi sorting and packaging pathway. Their presence suggests that differential sorting and packaging is possible during post-embryonic development, like in adults. The relationship of the differential expression of the two genes to the development of the caudodorsal cell system and its targets is discussed.