Selected Article

Title

Fishing for sex genes by chromosome microdissection in two tilapia species with different sex determining systems

Description

In the tilapia species group, the major sex determining factors have been located on Linkage Group 1 (LG1), on a small chromosome (Chr) pair in Oreochromis niloticus, on LG3 (the largest Chr pair) in O. aureus or on both, depending on populations/strains. LG3 has all the traits of an old sex chromosome, whereas LG1 seems to be an emerging one. Taking advantage of its large size, LG3-Chr has been microdissected to search for sex-linked genes. It was isolated from metaphase spreads of XX-female and YY-male in O. niloticus and of ZZ-male in O. aureus. Using cDNA capture and direct cDNA selection procedures we isolated various transposons but a reduced number of genes. We therefore compared three different whole genomic amplification (WGA) methods (DOP-PCR, GenomePlex and GenomiPhi) using a pool of 30 microdissected chromosomes, to evaluate the best LG3-Chr representation. Loci from 5 microsatellites, 2 genes and 2 uncoded fragments located on LG3-Chr have been searched by PCR on the DNA obtained by the 3 methods. GenomePlex and GenomiPhi gave 60 % loci amplification. GenomePlex probe produced the best painting probe, entirely covering the two LG3-Chrs with weaker signals in the gene-rich pericentromeric region, in both species, confirming that this pair is essentially composed of conserved and specific repeated sequences. This will allow to trace its history within the tilapia group. (Texte intégral)