Mechanisms controlling expression of the RAG locus during lymphocyte development

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Recombination activating genes (RAG)1 and RAG2 are crucial for immunoglobulin (Ig) and T cell receptor (TCR) gene rearrangement during lymphocyte development.
• RAG expression is tightly regulated by the products of the assembled antigen receptor genes, with surface expression and self-reactivity testing influencing RAG levels.

Purpose of the Study:

• To elucidate the mechanisms by which tonic receptor signaling reduces RAG expression in developing B and T lymphocytes.
• To understand how this reduction contributes to immune tolerance and prevents autoreactivity.

Main Methods:

• Investigated tonic signaling pathways in immature B cells and double-positive (DP) T cells.
• Analyzed the role of specific kinases (PI(3)K, Akt, Abl, Erk) and transcription factors (FoxO) in regulating RAG expression.

Main Results:

• In B cells, tonic signaling activates PI(3)K/Akt, leading to FoxO protein phosphorylation and cytoplasmic sequestration, thus inhibiting RAG transcription.
• In T cells, tonic signaling activates Abl/Erk kinases, resulting in the transcriptional inactivation of RAG genes.

Conclusions:

• Tonic receptor signaling is a key mechanism for downregulating RAG expression during lymphocyte maturation.
• This process is essential for establishing central tolerance by preventing the development of self-reactive lymphocytes.