Analysis of Mice with Single and Multiple Copies of Transgenes Reveals a Novel Arrangement for the λ5-V_preB1 Locus Control Region

Abstract

The murine λ5-V _preB1 locus encodes two proteins that form part of the pre-B-cell receptor and play a key role in B-lymphocyte development. We have identified a locus control region (LCR) which is responsible for coordinate activation of both genes in pre-B cells. Analysis of mice with single and multiple copies of transgenes shows a clear difference in the expression behavior of the genes depending on the transgene copy number. While expression of both λ5 and V _preB1 in single- and two-copy integrations requires the presence of a set of DNase I hypersensitive sites located 3′ of the λ5 gene, small fragments containing the genes have LCR activity when arranged in multiple-copy tandem arrays, indicating that additional components of the LCR are located within or close to the genes. The complete LCR is capable of driving efficient copy-dependent expression of a λ5 gene in pre-B cells even when it is integrated into centomeric γ-satellite DNA. The finding that activation of expression of the locus by positively acting factors is fully dominant over the silencing effect of heterochromatin has implications for models for chromatin-mediated gene silencing during B-cell development.

ACKNOWLEDGMENTS

We thank Norman Thompson and Donna Hawkesworth for technical assistance. We are grateful to Niels Gelhardt for providing the 129SV cosmid library. We thank Amanda Fisher, Matthias Merkenschlager, and Mauro Santibanez-Koref for discussions and critical reading of the manuscript.

This work was supported by the Medical Research Council, United Kingdom.