Investigations into the roles of Shroom3 in development and adult physiology

Abstract

The actin binding protein Shroom3 is best known for its role in mammalian neural tube closure through control of apical constriction and apicobasal elongation of epithelial cells. More roles for Shroom3 have recently been uncovered, both developmentally and postnatally, where its loss causes congenital heart and kidney defects and is genetically linked to chronic kidney disease in patients. However, questions still remain about the range of Shroom3 expression and the differences in its spatial and temporal functions. I hypothesize that Shroom3 has a wider postnatal expression range than previously understood, and that in organs with both developmental and postnatal expression, it is necessary for normal morphogenesis and physiology. Using a LacZ reporter system, postnatal Shroom3 expression was characterized in the brain, whisker pad, heart, lungs, intestines, kidney, ovary, uterus, testes, and bladder. Fluorescent staining with a custom Shroom3 antibody supported these results with additional expression in the retina. Many of these tissues do not demonstrate Shroom3’s characteristic apical constriction, suggesting that it has differing functions in other tissues. The heart and kidney were selected for further research due to having both developmental and postnatal expression and known phenotypes upon Shroom3 loss. Our lab previously found that global loss of Shroom3 during development resulted in congenital heart defects. Building on this, a novel floxed Shroom3 allele was used to create a myocardial specific knockout during development. Interestingly, no morphological defects were observed, suggesting that myocardial loss was not responsible for the known defects. The same floxed allele was used to induce Shroom3 loss in adult mice. After six months of monitoring, no morphological alterations in the kidneys were observed, and no changes in total urine soluble protein was seen. This suggests that kidney phenotypes from Shroom3 loss originate in development. Overall, this thesis presents evidence that Shroom3 expression in the adult mouse has a wider range than previously understood, evidence that Shroom3 acts in a non-cell autonomous manner and emphasizes the developmental impact of Shroom3 on postnatal physiological function. This raises that Shroom3 likely functions in different roles developmentally and postnatally, even in the same tissue.