Organization of Immunoglobulin Loci

Notes Due to polymorphism, the number of total and functional genes in different individuals (or mouse strains) can vary. The data shown here for the human loci were taken on 1/12/98 from a web site maintained by Ian Tomlinson at the MRC Centre for Protein Engineering http //www.mrc-cpe.cam.ac.uk/imt-doc/. See text for specific references. 

2 Functional as used here for the human loci means rearranged in vivo with a sequence appropriate for transcription and translation into a stable protein (see Tomlinson et al., 1995). A gene segment may have an open reading frame and no obvious defect, but is not counted as functional unless it is detected as a MD)/ rearrangement that appears to encode a protein that can form a stable three-dimensional structure. 

Genes Encoding Human and Mouse Kappa Chains 

Recently, a continuous physical map of the entire mouse k locus has been produced (George et al., 1995 Zocher et al., 1995 Kirschbaum et al., 1996 Schupp et al., 1997). The size of the locus is between 3 and 3.5 Mb. There is evidence for about 140 VK gene segments in the locus and a number of others are outside the locus. Individual members of a mouse VK family are frequently clustered in the same region (Heinrich et al., 1984 D Hoostelaere et al., 1988), but interspersion with members of different families is not uncommon (Zocher et al., 1995). Some 

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Ichihara, Y., Matsuoka, H., Kurosawa, Y. (1988b). Organization of human immunoglobulin heavy chain diversity gene loci. EMBO J. 7,4141-4150. 

Fig. 3. Organization of murine and human immunoglobulin loci. Each panel shows the murine (M.) and human (H.) immunoglobulin locus organization. Much of this figure is speculative. See text for details and references. Details of CM gene organization are reviewed by Honjo [5] and elsewhere in this volume.

This organization is shared by all V region loci. Heptamer/nonamer sequences are also conserved across loci, i.e. the same sequences are found in both immunoglobulin and TcR gene segments. This pattern of conservation suggests that these sequences are critical to recombination and that the recombination (joining) machinery has similar requirements in T and B cells. Indeed, this has already been shown to be the case ([30] and Chapter 4). 

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