Singh Group

Research Projects:

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

My laboratory has had a long-standing interest in the regulation of Ig gene transcription and recombination. We have been particularly focused on cell biological and molecular mechanisms that could facilitate long-range interactions between transcriptional elements such as promoters and enhancers or between DNA recombination signals flanking widely separated Ig gene segments.

Given the unusual structural organization of Ig gene loci (Mb size domains containing large numbers of iterated variable gene segments) we hypothesized that the transcription and recombination of these loci may also be regulated by nuclear compartmentalization and exceptional intra-chromosomal dynamics. Using immuno-FISH we were the first to demonstrate that Ig loci undergo developmentally regulated nuclear compartmentalization. The germline loci are associated with the nuclear lamina in multipotential hematopoietic progenitors and move away from the nuclear periphery in developing B- but not T-lineage cells as they prepare to undergo recombination. Furthermore, widely separated Ig gene segments appear to be more closely positioned in B-lineage nuclei suggesting the involvement of a structure that could facilitate long-range DNA recombination via DNA looping.

While studies on immunoglobulin (Ig) and other loci have correlated positioning at the nuclear lamina with gene repression, the functional consequence of this compartmentalization has remained untested. We have devised a new approach for inducible tethering of genes to the inner nuclear membrane (INM) and have demonstrated repositioning of chromosomal regions to the nuclear lamina. Such a mechanism likely contributes to the lineage-restricted activity of Ig loci. Our future studies in this area are directed at identifying and analyzing cis-elements and trans-factors that regulate the positioning of the IgH locus at the INM-nuclear lamina compartment.

See also:

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

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

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