Sites That Direct Nuclear Compartmentalization Are near the 5′ End of the Mouse Immunoglobulin Heavy-Chain Locus

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Abstract
VDJ rearrangement in the mouse immunoglobulin heavy chain (Igh) locus involves a combination of events, including a large change in its nuclear compartmentalization. Prior to rearrangement, Igh moves from its default peripheral location near the nuclear envelope to an interior compartment, and after rearrangement it returns to the periphery. To identify any sites in Igh responsible for its association with the periphery, we systematically analyzed the nuclear positions of the Igh locus in mouse non-B- and B-cell lines and, importantly, in primary splenic lipopolysaccharide-stimulated B cells and plasmablasts. We found that a broad ∼1-Mb region in the 5′ half of the variable-gene region heavy-chain (Vh) locus regularly colocalizes with the nuclear lamina. The 3′ half of the Vh gene region is less frequently colocalized with the periphery, while sequences flanking the Vh gene region are infrequently so. Importantly, in plasmacytomas, VDJ rearrangements that delete most of the Vh locus, including part of the 5′ half of the Vh gene region, result in loss of peripheral compartmentalization, while deletion of only the proximal half of the Vh gene region does not. In addition, when Igh-Myc translocations move the Vh genes to a new chromosome, the distal Vh gene region is still associated with the nuclear periphery. Thus, the Igh region that interacts with the nuclear periphery is localized but is likely comprised of multiple sites that are distributed over ∼1 Mb in the 5′ half of the Vh gene region. This 5′ Vh gene region that produces peripheral compartmentalization is the same region that is distinguished by requirements for interleukin-7, Pax5, and Ezh2 for rearrangement of the Vh genes.