Separable regulatory elements mediate the establishment and maintenance of cell states by the Drosophila segment-polarity gene gooseberry.

During Drosophila embryogenesis, position along the anteroposterior axis is specified within each segment by the products of the segment-polarity genes which include wingless (wg) and gooseberry (gsb). The striped expression of these genes in each segment is initially established by the pair-rule gene products during late blastoderm. This pattern is subsequently maintained after germ band extension by interaction among the segment-polarity genes themselves. Here we show that the maintenance of gsb, a PHox gene encoding a paired-domain and a homeodomain, is controlled by the wg signal, the homolog of the murine Wnt-1 protein. A control element responsible for wg-dependent maintenance of gsb expression, gsb-late element, is separable from an element required for the initial activation of gsb by pair-rule transcription factors, gsb-early element. The significance of such a regulatory strategy is discussed with respect to the establishment and maintenance of cell states within each segment by segment-polarity genes.