Expression patterns of smad family members during embryogenesis of the ascidian halocynthia roretzi

Abstract

The ascidian embryo has been long thought to show a mosaic mode of development. However, recent studies revealed significance of cell-cell communication during cleavage stages of embryogenesis. FGF and BMP signalings play critical roles in determination of cell types. Little is, however, known about regulation of competence of cells to the signals. Here we report the isolation of ascidian smad genes; Hrsmad4 which encodes a homolog of smad4 of vertebrates, Hrsmad6/7 which encodes a homologous gene of smad 6 and smad7 of vertebrates, and Hrsmad2/3 which encodes a homolog of smad2 and smad3 of vertebrates. The mRNAs of the isolated smad family genes were maternally inherited in egg and early embryos. While Hrsmad4 and Hrsmad6/7 RNAs distributed broadly in the early embryos, Hrsmad2/3 RNA was preferentially accumulated in the animal hemisphere.