How does organizer signaling influence the pattern of micromere fates?
After the 5th cleavage cycle, the D macromere cell (known as 3D) acts as an embryonic organizer to induce particular fates in the cells of the A, C and D lineages (Clement, 1962; Lambert and Nagy, 2001). We are testing candidate pathways that might mediate this signaling event, and looking at regulation of quartet-specific RNAs in response to organizer signaling. The mesendodermal blast cell 4d: a hallmark of spiralian development. One of the most striking commonalities shared by the diverse animal phyla that have spiralian development is the 4d cell (Lambert, 2008). In spiralians, this cell divides bilaterally to produce a pair of large mother cells that give rise to a stereotyped series of daughter cells. This lineage gives rise to the intestine, and most of the mesodermal organs like the retractor muscle and the heart. We have recently found that the IoNanos mRNA is required for multiple tissues derived from 4d. This result is surprising, since Nanos is not known to play roles in so
