The Shroom Family Proteins Play Broad Roles in the Morphogenesis of Thickened Epithelial Sheets

Thickened epithelial sheets are found in a wide variety of organ systems and the mechanisms governing their morphogenesis remain poorly defined. We show here, through expression patterns and functional studies, that Shroom family proteins are broadly involved in generating thickened epithelial sheets. Through in situ hybridization, we report the temporal and spatial expression patterns of the four Shroom family members during early Xenopus development, from oocytes to tadpole stage embryos. Further, we show that Shroom1 and 2 mRNAs are maternally expressed, while Shroom3 and Shroom4 are zygotic transcripts. In addition, maternal Shroom1 and 2 mRNAs localize in the animal hemisphere of the Xenopus egg and early blastula. During later development, all four Shroom family proteins are broadly expressed in developing epithelial organs, and the epithelial cells that express Shrooms are elongated. Moreover, we show that ectopic expression of Shroom2, like Shroom3, is able to increase cell height and that loss of Shroom2 function results in a failure of cell elongation in the neural epithelium. Together, these data suggest that Shroom family proteins play an important role in the morphogenesis of several different epithelial tissues during development. Developmental Dynamics 238:1480-1491, 2009. (C) 2009 Wiley-Liss, Inc.