Temperature and length-dependent modulation of the MH class II beta gene expression in brook charr (Salvelinus fontinalis) by a cis-acting minisatellite.
It is widely recognized that the variation in gene regulation is an important factor from which evolutionary changes in diverse aspects of phenotype can be observed in all organisms. Distinctive elements with functional roles on gene regulation have been identified within the non-coding part of the genome, including repeated elements. Major histocompatibility complex (MHC) genes have been the subject of an abundant literature which made them unique candidates for studies of adaptation in natural populations. Yet, the vast majority of studies on MHC genes have dealt with patterns of polymorphism in sequence variation while very few paid attention to the possible implication of differential expression in adaptive responses. In this paper, we report the identification of a polymorphic minisatellite formed of a 32 nucleotides motif (38% G+C) involved in regulation of the major histocompatibility class II beta gene (MHII beta) of brook charr (Salvelinus fontinalis). Our main objectives were: to analyze the variability of this minisatellite found in the second intron of the MHII beta gene and to document its effect to the variation of expression level of this gene under different environmental conditions. Distinctive number of the minisatellite repeats were associated with each different MHII beta alleles identified from exon 2 sequences. Relative expression levels of specific alleles in heterozygous individuals were determined from fish lymphocytes in different genotypes. We found that alleles carrying the longest minisatellite showed a significant 1.67-2.56-fold reduction in the transcript expression relatively to the shortest one. Results obtained in three different genotypes also indicated that the repressive activity associated to the longest minisatellite was more effective at 18 degrees C compared to 6 degrees C. In contrast, no significant difference was observed in transcript levels between alleles with comparable minisatellite length at both temperatures. We also depicted a significant up-regulation of the total MHII beta transcript at 6 degrees C relative to 18 degrees C. These results reveal for the first time that a temperature-sensitive minisatellite could potentially play an important role in the gene regulation of the adaptive immune response in fishes.
Croisetière
Sébastien
S
Département de Microbiologie et Immunologie, Université de Montréal, Montréal, Québec H3C 3J7, Canada. sebastien.croisetiere@umontreal.ca
Bernatchez
Louis
L
Belhumeur
Pierre
P
D000483:Alleles; D000818:Animals; D001482:Base Composition; D001483:Base Sequence; D029941:Fish Proteins / Q000235:genetics*; D020869:Gene Expression Profiling; D014644:Genetic Variation; D005838:Genotype; D000949:Histocompatibility Antigens Class II / Q000235:genetics*; D007438:Introns / Q000235:genetics; D018598:Minisatellite Repeats / Q000235:genetics*; D008969:Molecular Sequence Data; D011110:Polymorphism, Genetic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid; D013696:Temperature; D014337:Trout / Q000235:genetics*
D029941:Fish Proteins; D000949:Histocompatibility Antigens Class II