B Lymphocyte-Specific Loss of Ric-8A Results in a Gα Protein Deficit and Severe Humoral Immunodeficiency

Resistance to inhibitors of cholinesterase 8A (Ric-8A) is a highly evolutionarily conserved cytosolic protein initially identified in Caenorhabditis elegans, where it was assigned a regulatory role in asymmetric cell divisions. It functions as a guanine nucleotide exchange factor for G(alpha i), G(alpha q), and G(alpha 12/13) and as a molecular chaperone required for the initial association of nascent G alpha subunits with cellular membranes in embryonic stem cell lines. To test its role in hematopoiesis and B lymphocytes specifically, we generated ric8(fl/fl)vav1-cre and ric8(fl/fl)mb1-cre mice. The major hematopoietic cell lineages developed in the ric8(fl/fl) vav1-cre mice, notwithstanding severe reduction in G(alpha i2/3), G(alpha q), and G(alpha 13) proteins. B lymphocyte-specific loss of Ric-8A did not compromise bone marrow B lymphopoiesis, but splenic marginal zone B cell development failed, and B cells underpopulated lymphoid organs. The ric8(fl/fl)mb1-cre B cells exhibited poor responses to chemokines, abnormal trafficking, improper in situ positioning, and loss of polarity components during B cell differentiation. The ric8(fl/fl)mb1-cre mice had a severely disrupted lymphoid architecture and poor primary and secondary Ab responses. In B lymphocytes, Ric-8A is essential for normal Ga protein levels and is required for B cell differentiation, trafficking, and Ab responses.