Characterization of an ascidian DEAD-box gene, Ci-DEAD1: specific expression in the germ cells and its mRNA localization in the posterior-most blastomeres in early embryos

Abstract

We isolated DEAD-box genes from three ascidian species (Ciona intestinalis, Ciona savignyi, and Halocynthia roretzi) by polymerase chain reaction methods. We obtained two types from each of C. intestinalis and C. savignyi, and four types from H. roretzi. The first type (DEAD1) belonged to the vasa subfamily, the second type (DEAD2) to the PL10 subfamily, the third type (DEAD3) to the p68 subfamily, and the forth type (DEAD4) did not belong to any of the subfamilies. We further analyzed in detail the expression pattern of C. intestinalis vasa-type gene (Ci-DEAD1) by in situ hybridization. In sections of the ovary and testis, the Ci-DEAD1-specific probe reacted intensely to small germ cells, oogonium, and/or oocyte and spermatogonium and/or spermatocyte, respectively. In whole-mount specimens of juveniles this probe specifically reacted to the primordial germ cells in the gonad rudiment. These gonad-specific expressions were confirmed by reverse transcriptase polymerase chain reaction of RNA from various tissues. The transcript was present in unfertilized eggs and in the central cytoplasm of blastomeres until the two-cell stage. During the second cleavage a part of the transcripts moved to the posterior region of embryos and, during early embryogenesis, was localized in the posterior-most blastomeres. In the tailbud, one or two hybridization signals were detected in the caudal endodermal strand. Based on these observations, we propose precursors of primordial germ cells in ascidians.

Transient occurrence of vasa-expressing cells in nongenital segments during embryonic development in the oligochaete annelid Tubifex tubifex

“…In some organisms such as sea anemone, polychaete and medaka, maternally supplied vasa RNA is inherited by all of the early blastomeres and distributed evenly in each blastomere (Shinomiya et al 2000;Extavour et al 2005;Rebscher et al 2007). By contrast, at very early stages of development in red flour beetle, ascidians and some other teleosts (such as zebrafish, goldfish and loach), vasa RNA becomes localized into certain subcellular structures in early blastomeres (Yoon et al 1997;Braat et al 2000;Fujimura and Takamura 2000;Knaut et al 2000;Krφvel and Olsen 2002;Otani et al 2002;Fujimoto et al 2006;Schröder 2006;Shirae-Surabayashi et al 2006). In the oyster…”

Genetic Analysis of theCaenorhabditis elegansGLH Family of P-Granule Proteins

“…Perhaps the CCHC zinc fingers participate in RNA binding and compensate for the lack of an RGG domain in GLH family members. Interestingly, Ciona Vasa possesses a mix of FG and RG repeats, and the Vasa homologs in Ciona, Daphnia, Hydra, Artemia, and several other marine invertebrates contain CCHC zinc fingers (Fujimura and Takamura 2000;Sagawa et al 2005).…”

Repression of Zygotic Gene Expression in the Putative Germline Cells in Ascidian Embryos

“…Ultrastructural studies have shown that the CAB contains a matrix with high electron density, that resembles the germ plasm reported in other animals (Iseto and Nishida, 1999). Third, vasa mRNA and protein are characteristic of the germline cells of various animals (reviewed by Ikenishi, 1998), and maternal transcripts of Ci-DEAD1 , a vasa homolog in the ascidian, Ciona intestinalis , are concentrated in the posteriormost blastomeres (Fujimura and Takamura, 2000).…”