Specialized features of Rhynchosciara americana embryogenesis

Insect embryo development is a complex process which requires nuclear and c ellular division, cell shape alteration, and cell movement. This process ne eds to be orchestrated in a specific spatial and temporal fashion. Differen t insect species, despite similarities, present distinct morphogenetic path ways. We used the dipteran R. americana as a comparative model for embryo m orphogenesis studies, following embryo development with different histochem ical and immunohistochemical procedures. Despite the phylogenetic proximity with D. melanogaster, R. americana presents a peculiar morphogenesis. We s how that at the initial phases of development, from egg fertilization to bl astoderm formation, R. americana is similar to Drosophila. The first cleava ges are nuclear and cellularization only begins after nuclei spread through out the egg's cortex. However after this stage a series of cell movements e stablishes a short compact germ band anlage, which gastrulates in a pattern quite different from Drosophila. After gastrulation the germ band elongate s anterior-posteriorly and segmentation occurs simultaneously along the emb ryo. Embryo development from egg fertilization to larva hatching takes abou t 12 days. Our results show that R. americana presents a different morphoge netic pathway which does not fit in the current short, intermediate or long germ band classification. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.