Elucidation of IgH intronic enhancer functions via germ-line deletion.
Studies of chimeric mice demonstrated that the core Ig heavy chain (IgH) intronic enhancer (iEmu) functions in V(D)J and class switch recombination at the IgH locus. To more fully evaluate the role of this element in these and other processes, we generated mice homozygous for germ-line mutations in which the core sequences of iEmu (cEmu) were either deleted (cEmu(Delta/Delta) mice) or replaced with a pgk-Neo(R) cassette (cEmu(N/N) mice). The cEmu(Delta/Delta) mice had reduced B cell numbers, in association with impaired D to J(H) and V(H) to DJ(H) rearrangement, whereas cEmu(N/N) mice had a complete block in IgH V(D)J(H) recombination, confirming that additional cis elements cooperate with iEmu to enforce D to J(H) recombination. In addition, developing cEmu(Delta/Delta) and cEmu(N/N) B lineage cells had correspondingly decreased levels of germ-line transcripts from the J(H) region of the IgH locus (mu0 and Imu transcripts); although both had normal levels of germ-line V(H) transcripts, suggesting that cEmu may influence IgH locus V(D)J recombination by influencing accessibility of J(H) proximal regions of the locus. Consistent with chimera studies, peripheral cEmu(Delta/Delta) B cells had normal surface Ig and relatively normal class switch recombination. However, cEmu(Delta/Delta) B cells also had relatively normal somatic hypermutation of their IgH variable region genes, showing unexpectedly that the cEmu is not required for this process. The availability of mice with the iEmu mutation in their germ line will facilitate future studies to elucidate the roles of iEmu in V(H)(D)J(H) recombination in the context of IgH chromatin structure and germ-line transcription.
Perlot
Thomas
T
The CBR Institute for Biomedical Research, Inc., and Department of Genetics, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA.
Alt
Frederick W
FW
Bassing
Craig H
CH
Suh
Heikyung
H
Pinaud
Eric
E
D000818:Animals; D004252:DNA Mutational Analysis; D017931:DNA Primers; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D017353:Gene Deletion; D018390:Gene Targeting; D018095:Germ-Line Mutation / Q000235:genetics*; D017578:Immunoglobulin Class Switching / Q000235:genetics*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D007438:Introns / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D020133:Reverse Transcriptase Polymerase Chain Reaction
D017931:DNA Primers; D007143:Immunoglobulin Heavy Chains