Rhou maintains the epithelial architecture and facilitates differentiation of the foregut endoderm

Abstract

SUMMARYRhou encodes a Cdc42-related atypical Rho GTPase that influences actin organization in cultured cells. In mouse embryos at earlysomite to early-organogenesis stages, Rhou is expressed in the columnar endoderm epithelium lining the lateral and ventral wall of the anterior intestinal portal. During foregut development, Rhou is downregulated in regions where the epithelium acquires a multilayered morphology heralding the budding of organ primordia. In embryos generated from Rhou knockdown embryonic stem (ES) cells, the embryonic foregut displays an abnormally flattened shape. The epithelial architecture of the endoderm is disrupted, the cells are depleted of microvilli and the phalloidin-stained F-actin content of their sub-apical cortical domain is reduced. Rhou-deficient cells in ES cell-derived embryos and embryoid bodies are less efficient in endoderm differentiation. Impaired endoderm differentiation of Rhou-deficient ES cells is accompanied by reduced expression of c-Jun/AP-1 target genes, consistent with a role for Rhou in regulating JNK activity. Downregulation of Rhou in individual endoderm cells results in a reduced ability of these cells to occupy the apical territory of the epithelium. Our findings highlight epithelial morphogenesis as a required intermediate step in the differentiation of endoderm progenitors. In vivo, Rhou activity maintains the epithelial architecture of the endoderm progenitors, and its downregulation accompanies the transition of the columnar epithelium in the embryonic foregut to a multilayered cell sheet during organ formation.

Regulation and functions of RhoU and RhoV

“…RhoU-depleted cells had fewer apical microvilli and a reduction in subapical filamentous actin levels. This indicates that RhoU is important for epithelial architecture, 29 consistent with results in vitro with MDCK cells. 25 Apart from the regulation of cell adhesion and cell shape during development, RhoU plays a role in cell migration in developmental models.…”

“…[27][28][29] It contributes to the formation of cell-cell junctions between zebrafish cardiomyocytes through a pathway involving the GEF Arhgef7b and PAK1, thereby affecting cardiac morphogenesis. 27 It would be interesting to determine whether PAR6 is involved in RhoU signaling in zebrafish cardiomyocytes, similar to its role in MDCK epithelial cells.…”

“…3 RhoU also plays a role in regulating the development of the mouse foregut. 29,30 RhoU is expressed during embryogenesis in the epithelium of the developing gut. Once the epithelium becomes multi-layered RhoU expression decreases.…”

RNA-sequencing analysis reveals new alterations in cardiomyocyte cytoskeletal genes in patients with heart failure

“…38 RHOU is hypothesized to maintain the cell architecture through F-actin polarization, and future studies will elucidate the exact mechanisms of this regulation. 39,40 Another study reported that RHOU downregulation diminishes F-actin distribution, reducing the resistance of epithelial cells to compressive force. 41 Changes in RHOU expression may also affect cardiomyocyte resistance to blood pressure overload or other mechanical forces that occur during HF.…”

Development of the thyroid gland

“…Recent observations indicate that multilayering of the thyroid bud requires Cdc42-mediated apical constriction of progenitors centrally located in the thyroid placode (Loebel et al, 2016). By contrast, knockdown of Rhou, which encodes a Cdc42-related atypical Rho GTPase, paradoxically increases the size of the thyroid bud by a mechanism that appears to involve loss of apical polarity of budding cells (Loebel et al, 2011). Progression of thyroid budding by recruitment from adjacent endoderm might thus be facilitated by directed displacement of progenitors that acquire an unpolarized phenotype as they lose contact with the pharyngeal cavity (Fig.…”