An ascidian homologue of vertebrate BMPs-5–8 is expressed in the midline of the anterior neuroectoderm and in the midline of the ventral epidermis of the embryo

Abstract

The ascidian tadpole larva is thought to be the prototype for the ancestral chordate. Although ascidians show a highly determinate mode of development, recent studies suggest significant roles of cell-cell interaction during embryogenesis. To elucidate the signaling molecules responsible for the cellular interaction, we investigated an ascidian homologue of the transforming growth factor beta (TGF-beta) superfamily. HrBMPa is an ascidian member of the 60A subclass of the BMP subfamily. Molecular phylogenetic analysis suggested that HrBMPa branched prior to further divergence of vertebrate BMPs-5-8. The zygotic expression of HrBMPa was initiated around gastrulation. HrBMPa transcripts were first evident in precursor cells of the spinal cord, notochord, epidermis and nervous system, although signals in the first two regions quickly disappeared. In neurulae and early tailbud embryos, transcripts were evident in the adhesive organ, midline of the anterior dorsal neuroectoderm and midline of both ventral and dorsal ectoderm, suggesting that HrBMPa plays a major role in neuroectodermal cell differentiation during embryogenesis. This HrBMPa expression profile resembled that of Xenopus BMP-7, implying a primordial function of BMP-7 among vertebrate BMPs-5-8.

Nodal signaling regulates specification of ascidian peripheral neurons through control of the BMP signal

“…This difference may result from the distinct expression of BMP ligands between Halocynthia and Ciona. In Halocynthia, HrBMPa and HrBMPb are expressed in the dorsal and ventral midline of tailbud embryos (Miya et al, 1997(Miya et al, , 1996, but their Ciona orthologs, Ci-BMP2/4 and Ci-BMP5/7-like, are not (Imai et al, 2004). Here, we suggest that FGF/Nodal and BMP signals coordinate to induce caudal ESN formation in Halocynthia but do so independently in Ciona.…”

“…Two BMP genes, HrBMPa and HrBMPb, have been isolated from Halocynthia (Miya et al, 1997(Miya et al, , 1996. We injected HrBMPaMO, HrBMPbMO or a negative control MO (StdMO) into fertilized eggs.…”

“…7C,D). HrBMPa is normally expressed in lateral A-line neural plate cells (A9.29, A9.30, A9.31 and A9.32) and a-line neural plate cells, except for a9.34 and a9.38 (Miya et al, 1996; Fig. 7E,H).…”

“…Immunostaining for gelsolin, an ESN marker, was carried out using the AS23 monoclonal antibody. DIG-labeled RNA probes for gelsolin (Ohtsuka et al, 2001a), HrBMPa (Miya et al, 1996), HrBMPb (Miya et al, 1997), HrChordin (Darras and Nishida, 2001), HrPax-37 (Wada et al, 1997), HrEpiC (Ueki et al, 1991) and HrETR-1 (Yagi and Makabe, 2001) were synthesized using a DIG RNA-labeling Kit (Roche). The signal was detected by staining with NBT/BCIP or Fast Red (Roche).…”

Expression Patterns of Smad Family Members during Embryogenesis of the Ascidian Halocynthia roretzi

“…Endogenous FGF in the ascidian is not reported, while an FGF receptor-encoding cDNA is isolated (Kamei et al, 2000). On the other hand, molecular biological study on BMP signaling in the ascidian embryo has revealed that HrBMPa (BMPs 5-8 homolog) is expressed in presumptive epidermis (Miya et al, 1996), while HrBMPb (BMPs 2/4 homolog) is expressed only in the vegetal hemisphere in the gastrula (Miya et al, 1997). Overexpression of the BMPs in the whole embryo by injecting the synthetic RNA results in the neural-to-epidermal transformation in the anterior-most region of the tailbud embryo (Miya et al, 1997).…”