Transcription elongation factor ELOF1 is required for efficient somatic hypermutation and class switch recombination

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Somatic hypermutation (SHM) and class switch recombination (CSR) are essential processes for diversifying immunoglobulin (Ig) genes in B cells.
• These processes are initiated by the activation-induced deaminase (AID), a cytidine deaminase that acts on DNA during transcription by RNA polymerase II (RNAPII).
• The precise mechanisms and factors facilitating AID's access to its DNA substrate during transcription are not fully understood.

Purpose of the Study:

• To identify novel factors involved in the initiation of somatic hypermutation (SHM) and class switch recombination (CSR).
• To elucidate the role of elongation factor 1 homolog (ELOF1) in immunoglobulin gene diversification and B cell function.
• To understand how ELOF1 interacts with RNAPII and activation-induced deaminase (AID) to facilitate SHM and CSR.

Main Methods:

• Conducted a genetic screen to identify factors involved in SHM.
• Utilized mammalian B cell models to study the effects of ELOF1 loss on SHM, CSR, and AID activity.
• Analyzed RNAPII transcription dynamics, including pausing and phosphorylation patterns, in ELOF1-deficient cells.
• Investigated the requirement of transcription-coupled nucleotide excision repair (TC-NER) for SHM.

Main Results:

• Identified ELOF1 as a critical factor involved in SHM and CSR.
• Demonstrated that loss of ELOF1 impairs AID action, SHM, and CSR in B cells.
• Showed that ELOF1 deficiency alters RNAPII transcription, reducing pausing and affecting RNAPII phosphorylation.
• Confirmed that ELOF1 must bind to RNAPII to function in SHM/CSR and that TC-NER is not required for SHM.

Conclusions:

• ELOF1 plays a vital role in immunoglobulin gene diversification by facilitating AID activity.
• ELOF1 functions as a component of the RNAPII elongation complex, influencing transcription dynamics to create a suitable substrate for AID.
• The interaction of ELOF1 with RNAPII is essential for its role in SHM and CSR, independent of TC-NER.