MODRELL, M.S.*; PRICE, A.L; HANNIBAL, R.L.; PATEL, N.H.; Univ. of California, Berkeley; Univ. of Chicago; Univ. of California, Berkeley; Univ. of California, Berkeley: Regulation of early cell fates in the amphipod crustacean, Parhyale hawaiensis
Parhyale hawaiensis, an amphipod crustacean, displays total (holoblastic) cleavage during early embryogenesis, and we hope to determine how tightly cell lineage and cell fates are coupled in this species. In Parhyale, the first two divisions are radial, total, and slightly asymmetrical. The third division is highly asymmetric and produces an embryo that consists of four macromeres and four micromeres. Lineage studies performed at the eight-cell stage demonstrate that each cell normally contributes to only one of each of the germ layers (Gerberding et al, 2002). However, it is not known if these cells are specified or determined at this early stage. Cell ablations are a classical method for addressing how lineage is coupled to cell fate, and utilizing this approach at the eight cell stage, we find that there is much regulation which occurs between lineage restricted equivalency groups that give rise to the germline, mesoderm, and ectoderm. In addition, the molecular mechanisms involved in establishing the cell fate pattern in Parhyale are unknown. Therefore, we have taken a candidate gene approach to address this question. Armadillo/&beta-catenin is one such gene, as it is known to be involved in setting up cell fates in different organisms in a variety of cellular contexts. We have cloned the Parhyale ortholog of armadillo/&beta-catenin and examined its expression by in situ hybridization. Interestingly, at the earliest stages of development, maternally provided armadillo is present in what may be analogous to the �germplasm� or �nuage�, that then becomes restricted specifically to the germline. Additional ablation experiments, blastomere isolations, and mis-expression/knockdown experiments should further reveal the mechanisms behind asymmetric cell division and cell fates in Parhyale.
