A Stage-Specific Factor Confers Fab-7 Boundary Activity during Early Embryogenesis in Drosophila

Abstract

The Fab-7 boundary is required to ensure that the iab-6 and iab-7 cis-regulatory domains in the Drosophila Bithorax complex can function autonomously. Though Fab-7 functions as a boundary from early embryogenesis through to the adult stage, this constitutive boundary activity depends on subelements whose activity is developmentally restricted. In the studies reported here, we have identified a factor, called early boundary activity (Elba), that confers Fab-7 boundary activity during early embryogenesis. The Elba factor binds to a recognition sequence within a Fab-7 subelement that has enhancer-blocking activity during early embryogenesis, but not during mid-embryogenesis or in the adult. We found that the Elba factor is present in early embryos but largely disappears during mid-embryogenesis. We show that mutations in the Elba recognition sequence that eliminate Elba binding in nuclear extracts disrupt the early boundary activity of the Fab-7 subelement. Conversely, we find that early boundary activity can be reconstituted by multimerizing the Elba recognition site.

ACKNOWLEDGMENTS

We thank Greg Shanower, Daryl Gohl, Girish Deshpande, Gretchen Kappes, Jill Penn, and other members of our laboratory for helpful discussions, encouragement, and technical support during the course of these studies. We also thank Gordon Gray for providing fly food.

This work was supported by a National Institutes of Health grants to P.S. T.A. was supported by an Uehara Fellowship from the Uehara Memorial Foundation during 2001.