Differences in brain transcriptomes of closely related Baikal coregonid species

Abstract

The aim of this work was to get deeper insight into genetic factors involved in the adaptive divergence of closely related species, specifically two representatives of Baikal coregonids--Baikal whitefish (Coregonus baicalensis Dybowski) and Baikal omul (Coregonus migratorius Georgi)--that diverged from a common ancestor as recently as 10-20 thousand years ago. Using the Serial Analysis of Gene Expression method, we obtained libraries of short representative cDNA sequences (tags) from the brains of Baikal whitefish and omul. A comparative analysis of the libraries revealed quantitative differences among ~4% tags of the fishes under study. Based on the similarity of these tags with cDNA of known organisms, we identified candidate genes taking part in adaptive divergence. The most important candidate genes related to the adaptation of Baikal whitefish and Baikal omul, identified in this work, belong to the genes of cell metabolism, nervous and immune systems, protein synthesis, and regulatory genes as well as to DTSsa4 Tc1-like transposons which are widespread among fishes.

Figure 1

Identification of cDNAs corresponding to selected tags. cDNA synthesis was performed using the oligo(dT) primer. Double-stranded cDNA was hydrolyzed with PvuII followed by ligation to T7NotRsa suppression adapters (grey boxes). PCR primers are designated by arrows. “Tag” denotes an oligonucleotide primer designed according to the tag sequence found by SAGE.

Figure 2

Transcription levels of genes in the whitefish and omul brain estimated by real-time PCR. %: similarity of the PCR product to mRNA of known genes. The y-axis shows the number of transcripts normalized to the content of the GAPDH housekeeping gene. Data represent mean ± S.E. of six independent experiments.