Fig. 7. The micromere-PMC gene regulatory network. The total developmental time represented in the diagram is from fertilization (top) to the blastula stage (bottom). Arrows and bars indicate positive and negative interactions, respectively. All genes shown encode transcription factors with the exception of Delta, which encodes a transmembrane protein. There is evidence for a direct interaction between Ets1 and sm50 (Kurokawa et al., 1999) but all other interactions may be indirect. ß-catenin and Otx are maternal proteins that become differentially enriched in micromere nuclei at the 16-cell stage (Chuang et al., 1996; Logan et al., 1999). These two proteins are required for the activation of pmar1, which is expressed only by the micromeres and their progeny (Oliveri et al., 2002). Pmar1 may block the expression of a putative repressor (Repressor X) specifically in the micromeres. This repressor (which may be several proteins) blocks PMC fate specification in all non-micromere lineages (Oliveri et al., 2002). Ets1, alx1 and delta are all regulated independently by pmar1 and the repressor. Ets1 regulates the tbr gene (Fuchikami et al., 2002) and Alx1 regulates dri (this study). Alx1, Ets1 and Tbr are all expressed only by the large micromeres and their progeny. Alx1 and Ets1 both regulate genes involved in ingression and skeletogenesis (Kurokawa et al., 1999; this paper). Delta signaling activates genes involved in SMC specification, including gcm (Ransick et al., 2002; Sweet et al., 2002). PMC signals feed into the network upstream of alx1 (this study); dashed bars and dashed arrow show possible inputs.

Return to article