During B-cell development,antibody production switches from membrane-bound IgM to secreted antibody production.How does this switch occur?

Somatic recombination of the immunoglobulin heavy-gene locus first creates a rearranged gene that can express a membrane-bound μ chain.Antigen binding is required before the B cell can switch to secreted antibody production.The choice between membrane-bound versus secreted IgM depends on differential use of polyadenylation sites in the μ transcript.The μ transcript has two potential polyadenylation sites.If the downstream site is chosen,the resulting protein includes a C-terminal membrane anchor,which yields a membrane-bound form of μ .If the upstream polyadenylation site is used,the membrane anchor is bypassed,and the transcript is processed to yield the secreted version of the μ chain.