Afadin and RhoA control pancreatic endocrine mass via lumen morphogenesis

Abstract

Proper lumen morphogenesis during pancreas development is critical to endocrine and exocrine cell fate. Recent studies showed that a central network of lumens (termed core), but not the surrounding terminal branches (termed periphery), produces most islet endocrine cells. To date, it remains unclear how pancreatic lumens form and remodel and which aspects of lumen morphogenesis influence cell fate. Importantly, models testing the function of the central lumen network as an endocrine niche are lacking. Here, we identify mechanisms underlying lumen formation and remodeling and show that central lumen network morphogenesis impacts pancreatic endocrine mass. We show that loss of the scaffolding protein Afadin disrupts de novo lumenogenesis and lumen continuity in the tip epithelium. Codepletion of the actomyosin regulator RhoA and Afadin results in defects in the central lumens and arrests lumen remodeling. This arrest leads to prolonged perdurance of the central lumen network over developmental time and expansion of the endocrine progenitor population and, eventually, endocrine mass. Our study uncovers essential roles of Afadin and RhoA in pancreatic central lumen morphogenesis, which subsequently determines endocrine cell mass.

Deconstructing the principles of ductal network formation in the pancreas

“…It is more likely that cells are rearranged and recycled to widen or elongate contiguous ducts. The recent observation that Afadin and Ras homolog gene family member A (RhoA), acting upstream of microfilament dynamics, are needed for loop elimination is in agreement with this hypothesis [ 45 ]. This raises questions as to how cells sense the lowest flow and the fact that the duct is supernumerary.…”

ROCK-nmMyoII, Notch and Neurog3 gene-dosage link epithelial morphogenesis with cell fate in the pancreatic endocrine-progenitor niche

“…Moreover, perturbation in Pdx1 + epithelial cells of CELSR proteins, components of the Wnt/PCP ( planar cell polarity) signaling orthogonal to apico-basal polarity, caused large reductions in Neurog3 + cells (Cortijo et al, 2012). Other reports connect morphogenesis and differentiation via RhoA (Petzold et al, 2013;Azizoglu et al, 2017) and Rac signaling (Löf-Öhlin et al, 2017). An important link between Rac, apical domain size control and endocrine cell-fate acquisition occurs in mice and humans (Löf-Öhlin et al, 2017).…”

Robo signalling controls pancreatic progenitor identity by regulating Tead transcription factors

“…Indeed, our results show that Prox1-high and Pdx1-negative cells not only acquire hepatic gene expression, but also morphological features, which are reminiscent of embryonic liver cells 26 , 27 , 47 . Specifically, beside the reduced levels of E-cadherin, mutant Prox1-high cells display (i) changes in F-actin localisation, which accumulates at cell’s leading edge instead of the apical localisation typical in pancreatic bud cells 48 , 49 , (ii) laminin breakdown at the basement membrane and (iii) ectopic induction of Hex expression. During development, this set of events is required for the initiation of hepatoblast delamination and migration in the adjacent mesenchyme; previous work has shown that in the absence of Prox1 or Hex in the mouse, hepatic endoderm fails to migrate and to preserve cell differentiation 26 , 27 , 47 .…”