Mutations in human lymphocytes are commonly due to gene deletion. To investigate the mechanism of deletion for autosomal genes, we immunoselected lymphocytes mutated at the HLA-A locus and cloned them for molecular analysis. Of 36 mutant clones that showed deletion of the selected HLA-A allele, 8 had resulted from a simple gene deletion, whereas 28 had resulted from a more complex mutational event involving reduplication of the nonselected HLA-A allele as indicated by hybridization intensity on Southern blots. In 3 of the 28 clones, retention of heterozygosity at the HLA-B locus indicated that the reduplication was due to recombination between the two chromosomes 6; but in the remaining 25 clones, distinction could not be made between recombination and chromosome reduplication. The results indicate that mutations in normal somatic cells frequently result in hemizygosity or homozygosity at gene loci and, thereby, resemble the mutations thought to be important in the etiology of various forms of cancer.
Taking advantage of five mouse genomic or cDNA probes [KE5(probe 14), KE4 (probe 11), KE3 (probe 7), KE2 (probe 5), and SET] mapped on the H-2K region in mouse, we have identified and localized homologues of these five genes in the human major histocompatibility complex region (HKE5, HKE4, HKE3, HKE2, and HSET, respectively). Cosmid cloning and pulsed field gel electrophoresis analyses indicated that a human homologous gene, HKE5, is located 10 kilobases (kb) centromeric of the alpha 2 (XI) collagen (COL11A2) gene followed by HKE4. HKE3, closely linked to HKE2, is located 170 kb centromeric of HKE4. Furthermore, HSET is located 50 kb centromeric of HKE2. This gene organization outside the DP subregion is completely identical to that of the mouse H-2K region centromeric of I-Pb3, a mouse homologue of the DPB gene, except the lack of genes corresponding to the H-2K and -K2 genes in human.
The lens opacity directly decreases visual acuity. To date, neither prophylactic nor pharmacologic treatments have been effective in stopping or decreasing lens opacity. Although extracapsular cataract extraction followed by intraocular lens insertion is considered to be an effective treatment, postoperative proliferation of lens epithelial cells (LECs) disturbs the vision again. In the present study a monoclonal antibody (MAb) directed against bovine LECs was generated. The MAb (XC3-2-B1H9) reacted specifically with the cell membrane of LECs. No other tissues in bovine eyes, such as the cornea, iris, ciliary body, choroid, retina, or the sclera, or any other major bovine organs, such as lung, liver, spleen, and kidney, were associated. The specificity of XC3-2-B1H9 was confirmed both by immunohistochemistry and by immunoblotting. This MAb cross-reacts with dog LECs. Based on immunoblot analysis, XC3-2-B1H9 recognizes the band with a Mr of about 160 kD of the water-insoluble fraction of LECs. The subclass of these MAbs is IgG1 as determined by immunodiffusion. This MAb has the capacity to act as a component of an immunotoxin to target the LECs.
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