The distribution of cells containing FMRFamide-related molecules in the embryonic development of Ophryotrocha labronica (Polychaeta: Dorvilleidae)

The neurotransmitters are considered to be involved in early developmental processes of both neural and non neural tissue in invertebrates and vertebrates. In this context the distribution of Phe-Met-Arg-Phe-NH2 (FMRFamide)-like molecules were studied during Ophryotrocha labronica embryogenesis. This species is a small marine gonochoristic polychaete with a short direct development and characterized by several embryos at the same stage included in an egg mass. The FMRFamide-like molecules were first found at the one cell stage, in cleaving embryos mainly localized in specific blastomeres and in gastrular embryos. In early organ formation stage, the immunoreactivity occurred by the beginning of the central nervous system development and the first positive cell was located in an anterior area where the brain will differentiate. As embryogenesis proceeded, the organization of ventral segmental ganglia was marked by single reactive cells associated to positive processes. Immunoreactive cells were also found in digestive tract morphogenesis. Before hatching (6 days after fertilization), an higher number of positive nerve cells and fibres had been progressively added in embryo brain and the pattern of gut cells with FMRFamide-like phenotype had been established. The early presence from one cell stage and the distribution pattern of immunoreactive cells suggest that FMRFamide-related molecules may be acting as pre-nervous and growth regulatory signals in O. labronica embryogenesis.