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 w ith cDNA probes of about I kb when at least three adjacent copies of the ge ne are present. The immunoglobulin heavy chain locus is in the centre of th e long arm of chromosome 1. Previously, family studies showed that bona fid e MHC class Ib genes segregated independently. Now we show that MHC class I l alpha and beta genes and class Ib genes are on the same acrocentric chrom osome, with MHC in the middle of the long arm, the class Ib complex (XNC) a t 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 pseudote traploid X. laevis. (C) 2000 Elsevier Science Ltd. All rights reserved.