Control of a genetic regulatory network by a selector gene

The formation of many complex structures is controlled by a special class of transcription factors encoded by selector genes. It is shown that SCALLOPED, the DNA binding component of the selector protein complex for the Drosophila wing field, binds to and directly regulates the cis-regulatory elements of many individual target genes within the genetic regulatory network controlling wing development. Furthermore, combinations of binding sites for SCALLOPED and transcriptional effectors of signaling pathways are necessary and sufficient to specify wing-specific responses to different signaling pathways. The obligate integration of selector and signaling protein inputs on cis-regulatory DNA may be a general mechanism by which selector proteins control extensive genetic regulatory networks during development.

Skeletal morphogenesis in the sea urchin embryo: regulation of primary mesenchyme gene expression and skeletal rod growth by ectoderm-derived cues

The skeleton of the sea urchin embryo is synthesized by the primary mesenchyme cells (PMCs). Previous studies have shown that local interactions between PMCs and the neighboring ectoderm regulate several aspects of skeletal morphogenesis, including PMC distribution in the blastocoel, the size of the skeleton and its branching pattern. In the present study, we have further examined the regulation of skeletogenesis by the ectoderm. We generated a ‘rate map’ of skeletal growth, which revealed stereotypical changes in the rates at which specific skeletal elements elongate during development. We showed that three transcripts encoding PMC-specific gene products known to be involved in the synthesis of the skeleton exhibited dynamic, spatially regulated patterns of expression within the PMC syncytium. All three gene products showed high levels of expression at sites of skeletal rod growth, although the specific patterns varied among the genes. We present direct evidence, based upon cell transplantation experiments, that the expression of one of these genes, SM30, is responsive to local, ectoderm-derived cues. Based upon our studies, we suggest that short-range signals from different ectodermal territories may regulate the expression of PMC-specific gene products that are rate-limiting in skeletal biosynthesis, thereby locally influencing skeletal rod growth.