Specialized features of Rhynchosciara americana embryogenesis

Abstract

Insect embryo development is a complex process which requires nuclear and cellular division, cell shape alteration, and cell movement. This process needs to be orchestrated in a specific spatial and temporal fashion. Different insect species, despite similarities, present distinct morphogenetic pathways. We used the dipteran R. americana as a comparative model for embryo morphogenesis studies, following embryo development with different histochemical and immunohistochemical procedures. Despite the phylogenetic proximity with D. melanogaster, R. americana presents a peculiar morphogenesis. We show that at the initial phases of development, from egg fertilization to blastoderm formation, R. americana is similar to Drosophila. The first cleavages are nuclear and cellularization only begins after nuclei spread throughout the egg’s cortex. However after this stage a series of cell movements establishes a short compact germ band anlage, which gastrulates in a pattern quite different from Drosophila. After gastrulation the germ band elongates anterior–posteriorly and segmentation occurs simultaneously along the embryo. Embryo development from egg fertilization to larva hatching takes about 12 days. Our results show that R. americana presents a different morphogenetic pathway which does not fit in the current short, intermediate or long germ band classification.