Abstract
ABSTRACTEpithelial invagination is a morphological process in which flat cell sheets transform into three-dimensional structures through bending of the tissue. It is accompanied by apical constriction, in which the apical cell surface is reduced in relation to the basal cell surface. Although much is known about the intra-cellular molecular machinery driving apical constriction and epithelial invagination, information of how extra-cellular signals affect these processes remains insufficient. In this study we have established several in vivo assays of placodal invagination to explore whether the external signal BMP regulates processes connected to epithelial invagination. By inhibiting BMP activity in prospective cranial placodes, we provide evidence that BMP signals are required for RhoA and F-actin rearrangements, apical constriction, cell elongation and epithelial invagination. The failure of placode invagination after BMP inhibition appears to be a direct consequence of disrupted apical accumulation of RhoA and F-actin, rather than changes in cell death or proliferation. In addition, our results show that epithelial invagination and acquisition of placode-specific identities are two distinct and separable developmental processes. In summary, our results provide evidence that BMP signals promote epithelial invagination by acting upstream of the intracellular molecular machinery that drives apical constriction and cell elongation.
Highlights
Epithelial invagination is a morphological process in which flat cell sheets transform into three-dimensional structures, like an epithelial pit/sac/cup or a furrow
Bone Morphogenetic Protein (BMP) activity is detected in placodal regions around the time of invagination To study invagination we first characterized the timing of initial invagination in the olfactory, lens and otic sensory placodes in chick (Gallus gallus)
BMP is required for epithelial invagination By studying three different sensory placodes and one non-sensory placode we have unraveled a common mechanism, in which BMP
Summary
Epithelial invagination is a morphological process in which flat cell sheets transform into three-dimensional structures, like an epithelial pit/sac/cup or a furrow. Epithelial invagination is accompanied by apical constriction and cell elongation along their apical-basal axis Many studies have addressed the intra-cellular molecular machinery involved during epithelial invagination (reviewed in Chauhan et al, 2015; Kondo and Hayashi, 2015; Martin and Goldstein, 2014; Sawyer et al, 2010), less is known about extracellular signals that affect this process.
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