Neurocalcin-like immunoreactivity in embryonic stages of the gastropod molluscs Aplysia californica and Lymnaea stagnalis

Neurocalcin is a calcium-binding protein that has been localized in neural and non-neural tissues of vertebrates, the arthropod Drosophila melanogaster, and in juveniles and adults of the mollusc Aplysia californica. We examine the distribution of neurocalcin in pre-hatching stages of the molluscs A. californica and Lymnaea stagnalis to elucidate where this calcium-binding protein functions in early development, as well as to localize novel neuronal populations in early stages of ontogeny. Aplysia neurocalcin (ApNc)-like immunoreactivity was localized in shell-secreting cells in embryonic stages of both A. californica and L. stagnalis. In A. californica, central and anterior regions of the embryo were diffusely labeled, as were a few identifiable neurons in veliger stages. On the other hand, in L. stagnalis, ApNc-like immunoreactivity was clearly detected in cells and fibers in the same locations as neuronal elements that have been previously identified very early in development and throughout the embryonic period using techniques to localize specific transmitters and peptides. Furthermore, additional neurons are also identified with anti-ApNc in this species. Establishing the distribution of neurocalcin-like proteins in embryonic stages of these two molluscs provides the first step to understanding the role of such proteins during development.