Singh Group

Research Projects:

Regulation of discrete developmental transitions within the B-cell developmental pathway (Project II)

We have obtained novel insights into two major developmental transitions within the B cell developmental pathway, the pre-B to B and the B to plasma cell, by pursuing the genetic analysis of the transcription factor Pip/IRF-4. Pip (PU.1 interaction partner) is an immune system-specific member of the interferon regulatory factor (IRF) family that my laboratory cloned by collaborating with U. Storb’s group. The characterization of Pip (IRF-4) led to the identification of a second immune-specific IRF, ICSBP (IRF-8) that specifically interacts with PU.1. From a biochemical and structural standpoint, these complexes were particularly intriguing because Pip is recruited to its binding site on DNA by phosphorylated PU.1. Using a variety of biochemical and structural approaches, we have been analyzing the assembly of PU.1/Pip/DNA ternary complexes.

Pursuing the implications of our molecular studies, we demonstrated that B lineage cells lacking IRF-4 and IRF-8 undergo a precise developmental arrest at the cycling pre-B cell stage and are blocked for light-chain recombination. Using IRF-4,8-/- pre-B cells we have proceeded to demonstrate that two pathways converge to synergistically drive light-chain rearrangement. We have proposed that stage-specific activation of light-chain recombination during B cell development is ensured by a combination of acquired pre-BCR and attenuated IL-7 signaling.

Curiously, IRF-4 also regulates the B to plasma cell transition. This terminal differentiation program involves a transient developmental state (germinal center B cell) that enables Ig gene class switching and somatic hypermutation. Our laboratory and that of R. Dalla-Favera have independently demonstrated that IRF-4 regulates both isotype switching as well as plasma cell differentiation. Our molecular analysis has revealed that IRF-4 regulates these processes by controlling the expression of the AID and Blimp-1 genes, respectively. Importantly, we have proposed a gene regulatory network in which graded expression of IRF-4 regulates the transition from isotype switching to plasma cell differentiation.

See also:

>> Gene regulatory networks that dictate cell fate choices in the immune system (Project I)

>> Nuclear compartmentalization, transcription and recombination dynamics of immunoglobulin loci (Project III)

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