Meeting Abstract
Penaeid shrimp embryos develop by holoblastic cleavage to the 32-cell stage, when gastrulation is initiated by the ingression of two mesendoblasts, followed by invagination of nine naupliar mesoderm cells. The naupliar mesoderm cells give rise to the muscles of the first three pairs of head appendages – first and second antennae and mandibles. These dorsal and ventral appendage muscles produce the swimming movements of the nauplius larva. The ventral mesendoblast divides to produce the primordial mesoteloblast, which forms the posterior (teloblastic) mesoderm, and the primordial germ cell. The teloblastic mesoderm forms most of the mesoderm of the cephalothorax and abdomen. The muscles of the cephalothorax form during the late naupliar and protozoeal larval stages. A complex network of abdominal muscles develops through the third protozoeal and mysis larval stages to form the adult pattern in the postlarva. Two sets of developmental transcriptomes have recently been published, which have identified many developmental genes of interest in penaeid shrimp. Penaeid shrimp orthologs of genes hypothesized to be involved in mesoderm/muscle development (twist, snail, mef2, brachyury) and germ line (vasa, nanos, pumilio) were found. twist and snail are expressed from the limb bud stage embryo to the postlarva; mef2 is expressed from egg to postlarva, and brachyury is expressed only during gastrulation. A large RNA-rich granule is inherited by one of the mesendoblasts and may contain germ line determinants. By TEM, the granule contains smaller electron-dense granules, as well as mitochondria and multi-vesicular bodies. The function of selected mesoderm and germ line genes will be tested by RNA interference experiments. The results may yield insights into the evolution of development in decapod crustaceans and could be applied to shrimp aquaculture.
