Impaired B cell development and function in mice with a targeted disruption of the homeobox gene Hex

Abstract

Hex is a homeobox gene that is expressed in all stages of B cell development except plasma cells. We studied lymphocyte development in the absence of Hex by using the RAG1-deficient blastocyst complementation system because homozygous disruption of Hex is embryonic lethal. Hex ؊/؊ ;RAG1 ؊/؊ chimeric mice had severely reduced numbers of mature B cells, pre-B cells, and CD5 ؉ B cells with a striking 15-fold increase in the percentage of B220 ؊ CD19 ؉ cells in the bone marrow. Hex ؊/؊ ;RAG1 ؊/؊ chimeric mice failed to generate IgG antibodies to T cell-independent antigens, although their serum IgM levels and antibody responses to T cell-dependent antigens were intact. Therefore, Hex is necessary for B cell development and function and its absence results in a dramatic increase in B220 ؊ CD19 ؉ cells.

A null mutation ofHhexresults in abnormal cardiac development,defective vasculogenesis and elevated Vegfa levels

“…Hhex-deficient mice have multiple developmental defects, including marked abnormalities of heart and vascular development To determine the function of Hhex in vivo, we generated a null allele using a targeting construct designed to delete exons 1 and 2 of the Hhex genomic sequence, which removed the transcription start site, translational start site and most of the homeobox as previously described (Bogue et al, 2003). Homozygous deletion of Hhex results in embryonic lethality, as evidenced by the fact that we have detected no live born Hhex -/-mice and that the ratio of Hhex…”

“…The Hhex targeting construct and heterozygous ES cells were generated as previously described (Bogue et al, 2003). Two heterozygous clones were injected into C57BL/6J blastocysts to generate chimeric mice.…”

“…Mice homozygous for a disruption of the Hhex gene die at mid-gestation (E13.5-E15.5) and have defects in forebrain, thyroid, monocyte and liver development (Keng et al, 2000;Martinez Barbera et al, 2000) (C. W. Bogue, unpublished). Recent data from our laboratory indicate that disruption of the Hhex gene also leads to a profound block in B-cell development (Bogue et al, 2003). In addition, investigators using in vitro Hhex -/-embryonic stem (ES) cell differentiation, in vivo yolk sac hematopoietic progenitor assays, and chimeric mouse analysis, found that Hhex is required for differentiation of the hemangioblast to definitive embryonic hematopoietic progenitors and, to a lesser extent, endothelial cells (Guo et al, 2003).…”

The homeobox gene Hex induces T-cell-derived lymphomas when overexpressed in hematopoietic precursor cells

“…Hex expression is downregulated during terminal differentiation of B cells, suggesting that Hex is involved in B-cell development (Manfioletti et al, 1995). Mice generated from chimeric blastocysts composed of HexÀ/À and RAGÀ/À ES cells are defective in normal B-cell development and function but have normal T-cell differentiation (Bogue et al, 2003). Recently, it has been demonstrated that transgene-driven expression of Hex in thymocytes disrupts normal T-cell development, resulting in fewer double-positive and more CD8 þ cells in the thymus and decreased numbers of T cells in the periphery (Mack et al, 2002).…”

A crucial role for the homeodomain transcription factor Hhex in lymphopoiesis

“…To overcome the embryonic lethality of Hhex and investigate its role in hematopoietic development, blastocyst complementation and embryoid body differentiation approaches have been used. Using blastocyst compensation of Rag1 2/2 mice, it has been shown that Hhex is required for B-cell development and function, 16 whereas, in embryonic stem cell differentiation models, Hhex is required for maturation and proliferation of definitive HSCs. [17][18][19] Thus, Hhex is postulated to play a role in hematopoietic differentiation and stem cell self-renewal in the adult.…”