Phenotypic and Molecular Alterations in the Mammary Tissue of R-Spondin1 Knock-Out Mice during Pregnancy

Abstract

<div><p>R-spondin1 (Rspo1) is a member of a secreted protein family which has pleiotropic functions in development and stem cell growth. <i>Rspo1</i> knock-out mice are sex-reversed, but some remain sub-fertile, so they fail to nurse their pups. A lack of <i>Rspo1</i> expression in the mammary gland results in an absence of duct side-branching development and defective alveolar formation. The aim of this study was to characterize the phenotypic and molecular alterations of mammary gland due to <i>Rspo1</i> knock-out. Using the transcriptional profiling of mammary tissues, we identified misregulated genes in the mammary gland of <i>Rspo1</i> knock-out mice during pregnancy. A stronger expression of mesenchymal markers was observed, without modifications to the structure of mammary epithelial tissue. Mammary epithelial cell immunohistochemical analysis revealed a persistence of virgin markers, which signify a delay in cell differentiation. Moreover, serial transplantation experiments showed that Rspo1 is associated with a regenerative potential of mammary epithelial cell control. Our finding also highlights the negatively regulated expression of Rspo1’s partners, <i>Lgr4</i> and <i>RNF43</i>, in the mammary gland during pregnancy. Moreover, we offer evidence that Tgf-β signalling is modified in the absence of Rspo1. Taken together, our results show an abrupt halt or delay to mammary development during pregnancy due to the loss of a further differentiated function.</p></div