Abstract
The essential events of B-cell development are the stochastic and sequential rearrangement of immunoglobulin heavy (Igμ) and then light chain (Igκ followed by Igλ) loci. The counterpoint to recombination is proliferation, which both maintains populations of pro-B cells undergoing Igμ recombination and expands the pool of pre-B cells expressing the Igμ protein available for subsequent Igκ recombination. Proliferation and recombination must be segregated into distinct and mutually exclusive developmental stages. Failure to do so risks aberrant gene translocation and leukemic transformation. Recent studies have demonstrated that proliferation and recombination are each affected by different and antagonistic receptors. The IL-7 receptor drives proliferation while the pre-B-cell antigen receptor, which contains Igμ and surrogate light chain, enhances Igκ accessibility and recombination. Remarkably, the principal downstream proliferative effectors of the IL-7R, STAT5 and cyclin D3, directly repress Igκ accessibility through very divergent yet complementary mechanisms. Conversely, the pre-B-cell receptor represses cyclin D3 leading to cell cycle exit and enhanced Igκ accessibility. These studies reveal how cell fate decisions can be directed and reinforced at each developmental transition by single receptors. Furthermore, they identify novel mechanisms of Igκ repression that have implications for gene regulation in general.
Highlights
Development of a diverse repertoire of peripheral B cells is dependent on the appropriate and ordered progression of Blymphopoiesis
Successful expression of a functional Igμ capable of pairing with surrogate light chain (SLC) components and Igα/Igβ to form the pre-B-cell receptor at the cell surface is associated with a proliferative burst that expands the pool of pre-B cells expressing Igμ prior to cell cycle exit and the rearrangement of Igκ
B-CELL DEVELOPMENT Interactions with bone marrow (BM) stromal cells induce the differentiation of common lymphoid progenitor cells (CLPs), capable of generating B and T cells, into multipotential precursor– progenitor B cells [1, 2]
Summary
This process occurs through discrete developmental stages driven by the sequential rearrangement and expression of genes encoding the immunoglobulin heavy (Igμ) and light chains (Igκ or Igλ). B-CELL DEVELOPMENT Interactions with bone marrow (BM) stromal cells induce the differentiation of common lymphoid progenitor cells (CLPs), capable of generating B and T cells, into multipotential precursor– progenitor (pre–pro) B cells [1, 2] At this stage, initial Igμ rearrangements occur at diversity (DH) and joining (JH) gene segments [3]. It is not clear if this means that the pre-BCR censors autoreactivity or if autoreactivity, and ligation by self-antigen, is required to complement SLC deficiency
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