Rho signalling restriction by the RhoGAP Stard13 integrates growth and morphogenesis in the pancreas

Abstract

SUMMARYThe development of functional organ architecture relies on coordinated morphogenesis and growth. In the developing pancreas, the branching epithelium is organised in discrete domains, delineating one specific domain of progenitor cells at the tip of the branches. The molecular mechanisms underlying the coordinated action of branching and proliferation in organ formation are largely unknown. Here, we identify the RhoGAP protein Stard13 as an essential regulator of pancreas tissue architecture in the mammalian embryo. Conditional ablation of Stard13 expression in the pancreas disrupts epithelial morphogenesis and tip-domain organisation, resulting in hampered proliferation of tip progenitors and subsequent organ hypoplasia. Stard13 acts by regulating Rho signalling spatially and temporally during pancreas development. Our findings provide new insights into the mechanisms that shape pancreatic epithelium to create a mature organ and establish a functional link between Rho-mediated control of epithelial remodelling and organ size determination, involving reciprocal interaction of actin-MAL/SRF and MAPK signalling pathways.

Feedback control of growth, differentiation, and morphogenesis of pancreatic endocrine progenitors in an epithelial plexus niche

“…For instance, a requirement for Cdc42-mediated apicobasal polarization has already been linked to the generation of an endocrine differentiation-competent progenitor pool (Kesavan et al 2009) and could thus be considered as a central contributor to the generation of the plexus. Additionally, ablation of Strad13, a negative regulator of RhoA-ROCK-nmMyoII, reduces the size and replicative activity of pancreatic MPCs (Petzold et al 2013), and defects in planar cell polarity are associated with reduced Ngn3 + cell numbers (Cortijo et al 2012). While the detailed mechanistic underpinnings causing defective endocrine lineage development in these cases remain unclear, the picture emerging is that insights into how endocrine progenitors and committed endocrine precursors are efficiently maintained and generated, respectively, may be gleaned from characterizing, with increased spatiotemporal resolution, how cytoskeletal dynamics, cell polarity, actomyosin contractility, and/or the trafficking and distribution of receptors such as Notch functionally link cell and tissue morphogenesis processes with cell fate determination.…”

RhoGAP control of pancreas development

“…Specifically, Stard13 mutant cells remained stratified, cuboidal in shape and did not properly form and resolve "rosette-like" structures. 16,20 In addition, we found that mutant cells display alterations in the actomyosin cytoskeletal organization, including not only an accumulation of F-actin and myosin, but also their irregular distribution throughout the cytoplasm. 16 Collectively, these results suggest that Stard13 is required for ensuring epithelial remodeling and initiation of branching in the pancreas.…”

“…16,20 In addition, we found that mutant cells display alterations in the actomyosin cytoskeletal organization, including not only an accumulation of F-actin and myosin, but also their irregular distribution throughout the cytoplasm. 16 Collectively, these results suggest that Stard13 is required for ensuring epithelial remodeling and initiation of branching in the pancreas. The fact that epithelial defects (e.g., aberrant cell shape and F-actin accumulation) were the earliest detectable defects in the mutant thereby, control morphogenesis in a variety of epithelial tissues.…”

“…Our detailed phenotypic analysis suggests that loss of Stard13 affects pancreatic epithelium starting from E11.5, which coincides with the initiation of the transition from a stratified unpolarized epithelium into a polarized monolayer of cells. 16,19 Upon closer examination of cell morphology, polarity, and cytoskeletal organization, we observed that Stard13 PA-deleted embryos show major problems in epithelial remodeling. Specifically, Stard13 mutant cells remained stratified, cuboidal in shape and did not properly form and resolve "rosette-like" structures.…”

“…Strikingly, the proliferative defects almost exclusively affected the progenitor cells (Cpa1 + ;pHH3 + cells), while proliferation rate in the rest of the epithelium was similar to control counterparts. 16 In addition to a decreased proliferative activity, Cpa1 + progenitor cells appeared mislocalized and randomly distributed throughout the tissue, being the tip structures not properly formed in the mutant. 16 These observations suggest that the RhoGAP Stard13 plays an important role in sustaining proliferating progenitor cells in the embryonic pancreas.…”