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Atlantic cod (Gadus morhua) hemoglobin genes: multiplicity and polymorphism
Tudor Borza1, Cynthia Stone, A Kurt Gamperl
1Genome Atlantic, NRC Institute for Marine Biosciences, Halifax, NS B3H 3Z1, Canada. tborza@genomeatlantic.ca
BMC Genetics
|September 5, 2009
Summary
Atlantic cod possess more hemoglobin genes than previously known. This discovery suggests a greater capacity for adapting to environmental changes like hypoxia and temperature shifts.
Area of Science:
- Genomics
- Molecular Biology
- Aquaculture
Background:
- Hemoglobin (Hb) polymorphism in Atlantic cod (Gadus morhua) has traditionally been studied using protein gel electrophoresis, focusing on a single polymorphic locus with two alleles (HbI-1 and HbI-2).
- Previous research indicated the presence of multiple Hb genes in Atlantic cod, prompting a re-evaluation of the established genetic model.
- This study aimed to identify all expressed Hb genes and associated polymorphisms relevant for selective breeding programs.
Purpose of the Study:
- To re-evaluate the number of expressed hemoglobin genes in Atlantic cod.
- To identify polymorphisms within these genes that may influence phenotypic traits.
- To provide insights for potential applications in selective breeding programs for Atlantic cod.
Main Methods:
- Expressed Sequence Tags (ESTs) were analyzed to identify distinct hemoglobin transcripts.
- Genomic DNA sequencing was performed on Atlantic cod with known HbI genotypes (HbI-1/1, HbI-1/2, HbI-2/2) and their progeny.
- Reverse Transcription Polymerase Chain Reaction (RT-PCR) and Quantitative PCR (Q-PCR) were used to analyze gene expression levels.
Main Results:
- Nine distinct Hb transcripts were identified: four alpha and five beta Hb genes.
- Beta Hb genes showed higher polymorphism, with two major allele types (beta1A and beta1B) in the beta1 gene, linked to the previously identified HbI-1 and HbI-2 alleles.
- All nine Hb genes are expressed in adult fish, with varied expression levels, notably higher in individuals with the HbI-2/2 genotype.
Conclusions:
- Atlantic cod express more Hb genes than previously understood, with nine identified.
- The simultaneous expression of multiple Hb genes suggests an adaptive capacity to environmental stressors like hypoxia and temperature changes.
- A specific non-conservative substitution (Lys62Ala) in the beta1 Hb gene likely explains the HbI-1/HbI-2 polymorphism, warranting further investigation into its functional significance.
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