Antisense transcripts of V(D)J rearrangements; artifacts caused by false priming?

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Somatic hypermutation (SH) diversifies immunoglobulin (IG) genes during the germinal center response.
• Activation-induced cytidine deaminase (AID) initiates SH by deaminating cytosine in single-stranded DNA (ssDNA).
• SH is transcription-dependent, with proposed bidirectional transcription facilitating DNA accessibility for AID.

Purpose of the Study:

• To develop a quantitative method to study directional transcription across V(D)J rearrangements.
• To investigate the presence of antisense transcripts in human B cells and their role in SH.

Main Methods:

• Developed a quantitative method to assess directional transcription.
• Controlled for reverse transcription efficiency and specificity to avoid false positives.
• Analyzed transcription in the Ramos cell line, human blood B cells, and tonsil cells.

Main Results:

• The developed method accurately quantifies directional transcription.
• No antisense transcripts were detected in exonic or intronic regions of the hypermutation domain in tested human B cells.
• This provides strong evidence against the necessity of antisense transcripts for SH in human B cells.

Conclusions:

• Antisense transcripts are rare or absent in human B cells.
• The proposed model of bidirectional transcription facilitating SH requires re-evaluation.
• Further research is needed to understand the precise mechanisms of DNA accessibility for AID in SH.