Major histocompatibility complex and immunoglobulin loci visualized by in situ hybridization on Xenopus chromosomes

A technique for fluorescent in situ hybridization (FISH) on chromosomes of the amphibian Xenopus laevis is described. Positive results were obtained with cDNA probes of about I kb when at least three adjacent copies of the gene are present. The immunoglobulin heavy chain locus is in the centre of the long arm of chromosome 1. Previously, family studies showed that bona fide MHC class Ib genes segregated independently. Now we show that MHC class Il alpha and beta genes and class Ib genes are on the same acrocentric chromosome, with MHC in the middle of the long arm, the class Ib complex (XNC) at the tip or the same arm. Each locus or complex is found on only one pair of chromosomes confirming the diploidization of these genes in the pseudotetraploid X. laevis. (C) 2000 Elsevier Science Ltd. All rights reserved.