We have cloned a putative ascidian glycine-rich RNA binding protein gene, CiGRP1. Its maternal transcript and protein are stored in the unfertilized egg. They are gradually decreased during the first few rounds of cleavage. The CiGRP1 zygotic transcript and protein start to accumulate at the gastrula stage. The CiGRP1 transcript is expressed in the brain precursor and mesenchyme precursor cells of the gastrula and the neurula stage, and the brain and mesenchyme cells of the tailbud stage embryo. The CiGRP1 protein is found in all nuclei and in the cytoplasm of brain and mesenchyme cells. Although many glycine-rich RNA binding protein homologs of plants and vertebrates are cold-inducible, CiGRP1 cannot be induced by cold shock or heat shock at the transcriptional and translational levels during embryogenesis. The temporal expression pattern and the tissue-restricted expression pattern of CiGRP1 suggest that it has important roles in the very early stage of development and in the brain and the mesenchyme tissue specification.