IMGT®, the international ImMunoGeneTics information system®

Cassette

A cassette corresponds to the organization of small units at the genomic DNA level. Cassettes are found, for example, for chondrichthyes (shark, skate) Ig-Heavy (IGH) genes and for teleostei Ig-Light-Iota (IGI) genes.

Chondrichtyes IGH cassettes

• Chondrichtyes IGH cassettes comprise V-GENE, D-GENE, J-GENE and C-GENE.
• The V-D-J rearrangements seem to occur only within a given cassette and not between cassettes.
• The number of cassettes may reach several hundreds and may be localized on different chromosomes.
• In the chondrichthyes IGH cassettes partial V-D (~VD) or V-D, D-J (~VD,DJ) rearrangements or complete V-D-J (~VDJ) rearrangements are observed in the genomic DNA of any cell of the organism. This is in constrast with other vertebrates in which V-D-J rearrangements only occur in cells belonging to the B and T lineage, for the IG and TR genes respectively.
• It is probable that partially joined ~VD or ~VD,DJ DNA can complete the V-D-J rearrangement in B cells and be transcribed into fully rearranged cDNA (#c).

Teleostei IGI cassettes

• Teleostei IGI cassettes comprise V-GENE, J-GENE and C-GENE.
• The V-J rearrangements seem to occur only within a given cassette and not between cassettes, but this needs to be confirmed by more data.
• Two cassette types are defined, depending from the orientation of transcription of the V-GENEs relative to the J-GENE and C-GENE,
  • Cassette type 1: The V-GENE(s) is (are) in inverted orientation of transcription relative to the J-GENE and C-GENE,
  • Cassette type 2: The V-GENE(s) is (are) in the same orientation of transcription relative to the J-GENE and C-GENE.