The ARID domain protein drill is necessary for TGFβ signaling in Xenopus embryos

ARID domain proteins are members of a highly conserved family involved in chromatin remodeling and cell-fate determination. Drill is the founding member of the ARID family and is involved in developmental processes in both Drosophila and Caenorhabditis elegans. We describe the first embryological characterization of this gene in chordates. Drill mRNA expression is spatiotemporally regulated and is detected in the involuting mesoderm during gastrulation. Inhibition of drill by either a morpholino or an engrailed repressor-drill DNA binding domain fusion construct inhibits gastrulation and perturbs induction of the zygotic mesodermal marker Xbra and the organizer markers chordin, noggin, and Xlim1. Xenopus tropicalis drill morphants also exhibit impaired gastrulation and axial deficiencies, which can be rescued by coinjection of Xenopus laevis drill mRNA. Loss of drill inhibits the response of animal caps to activin and secondary axis induction by smad2. Drill depletion in animal caps prevents both the smad2-mediated induction of dorsal mesodermal and endodermal markers and the induction of ventral mesoderm by smad1. Mesoderm induction by eFGF is uninhibited in drill morphant caps, reflecting pathway specificity for dril 1. These experiments identify dril I as a novel regulator of TGFbeta signaling and a vital component of mesodermal patterning and embryonic morphogenesis. (C) 2004 Elsevier Inc. All rights reserved.