taiman (tai), a gene encoding a steroid receptor coactivator-like protein, is required for border cell migration in Drosophila ovaries. J. Bai , Y. Uehara , D.J. Montell. Dept Biological Chemistry, Johns Hopkins Univ Sch Med, Baltimore, MD.

   Steroid hormones and steroid hormone receptors are well known to play important roles in cell fate determination, proliferation and metamorphosis.The function of mammalian steroid hormone receptors is regulated by ligand-dependent association with transcriptional coactivators. However, steroid hormone receptor coactivators have been thought to be absent in the invertebrates. Here, we report identification of the gene, named taiman (tai) which encodes a steroid receptor coactivator-like protein in Drosophila. The tai gene was identified in a screen for mutations that cause border cell migration defects in mosaic clones. The predicted TAI protein contains bHLH-PAS domains, LXXLL domains and glutamine rich domains. TAI proteins is localized in the nuclei of all follicle cells, and is required for border cell migration cell-autonomously. Our results indicate that steroid hormone signaling is not only required for cell fate determination, proliferation and metamorphosis, but is also involved in regulating cell motility after cell fate determination is complete. Furthermore, tai interacts dominantly with two other border cell migration mutants but does not affect expression of slbo (slow border cells) (Montell et al., 1992) or its targets. Therefore, we propose that border cell migration requires both hormone-dependent and slbo-dependent transcriptional regulatory pathways.