Role of Rho kinases in B cell development

Abstract

Abstract Cytoskeletal rearrangement is a critical component to hematopoietic stem cell development and differentiation into mature leukocyte populations. A number of chemokines and biolipids have been shown to regulate these events via binding to G protein coupled receptors. Many of these receptors couple to the Ga12/13 family of G proteins to regulate actin reorganization via the RhoA small GTPase. The Rho-kinases, Rock1 and Rock2, are activated downstream of RhoA to induce cytoskeletal changes that regulate numerous cellular processes, including contraction, polarity, proliferation, motility, adhesion and viability. A role for RhoA in regulating hematopoiesis and subsequent leukocyte development has been established using genetic studies. However, a similar role for the Rock1 and Rock2 has not been demonstrated. As global deletion of either kinase causes embryonic lethality, we used conditional gene targeting to ablate either the Rock1 or Rock2 allele in adult mice. Rock1flox/flox or Rock2flox/flox mice were crossed to the Rosa26-Cre ERT2 line to globally delete the floxed alleles with tamoxifen. In contrast to deletion of RhoA, conditional deletion of either Rock1 or Rock2 was well-tolerated, with no aberrant effects on hematopoiesis. These results suggest functional redundancy between Rock1 and Rock2 in regulating RhoA activity in hematopoiesis. However, we observed a significant decrease in marginal zone B cell number and frequency in the spleen of mice lacking Rock1. We also observed a follicular B cell defect in the spleen of mice lacking Rock2. These results are consistent with the known roles of GPCRs in B cell migration/positioning, and suggest there are isoform specific functions of these kinases.