Côté Guillaume, Perry Guy, Blier Pierre, Bernatchez Louis
Département de biologie, Université Laval, Québec, Québec, Canada.
BMC Genet. 2007 Dec 21;8:87. doi: 10.1186/1471-2156-8-87.
Quantitative reaction norm theory proposes that genotype-by-environment interaction (GxE) results from inter-individual differences of expression in adaptive suites of genes in distinct environments. However, environmental norms for actual gene suites are poorly documented. In this study, we investigated the effects of GxE interactions on levels of gene transcription and growth by documenting the impact of rearing environment (freshwater vs. saltwater), sex and genotypic (low vs. high estimated breeding value EBV) effects on the transcription level of insulin-like growth factor (IGF-1) and growth hormone receptor (GHR) in brook charr (Salvelinus fontinalis).
Males grew faster than females (micro female symbol = 1.20 +/- 0.07 g.d-1, micro male symbol = 1.46 +/- 0.06 g.d-1) and high-EBV fish faster than low-EBV fish (microLOW = 0.97 +/- 0.05 g.d-1, muHIGH = 1.58 +/- 0.07 g.d-1; p < 0.05). However, growth was markedly lower in saltwater-reared fish than freshwater sibs (microFW = 1.52 +/- 0.07 g.d-1, microSW = 1.15 +/- 0.06 g.d-1), yet GHR mRNA transcription level was significantly higher in saltwater than in freshwater (microSW = 0.85 +/- 0.05, microFW = 0.61 +/- 0.05). The ratio of actual growth to units in assayed mRNA ('individual transcript efficiency', iTE; g.d-1.u-1) also differed among EBV groups (microLOW = 2.0 +/- 0.24 g.d-1.u-1; microHIGH = 3.7 +/- 0.24 g.d-1.u-1) and environments (microSW = 2.0 +/- 0.25 g.d-1.u-1; microFW = 3.7 +/- 0.25 g.d-1.u-1) for GHR. Males had a lower iTE for GHR than females (micro male symbol = 2.4 +/- 0.29 g.d-1.u-1; micro female symbol = 3.1 +/- 0.23 g.d-1.u-1). There was no difference in IGF-1 transcription level between environments (p > 0.7) or EBV groups (p > 0.15) but the level of IGF-1 was four times higher in males than females (micro male symbol = 2.4 +/- 0.11, micro female symbol = 0.58 +/- 0.09; p < 0.0001). We detected significant sexual differences in iTE (micro male symbol = 1.3 +/- 0.59 g.d-1.u-1; micro female symbol = 3.9 +/- 0.47 g.d-1.u-1), salinities (microSW = 2.3 +/- 0.52 g.d-1.u-1; microFW = 3.7 +/- 0.53 g.d-1.u-1) and EBV-groups (microLOW = 2.4 +/- 0.49 g.d-1.u-1; microHIGH = 3.8 +/- 0.49 g.d-1.u-1). Interaction between EBV-group and environment was detected for both GHR (p = 0.027) and IGF-1 (p = 0.019), and for iTE in the two genes (p < 0.0001; p < 0.05, respectively), where increased divergence in levels of GHR and IGF-1 transcription occurred among EBV-groups in the saltwater environment.
Our results show that both environment and sex have major impacts on the expression of mRNA for two key genes involved in the physiological pathway for growth. We also demonstrate for the first time, at least in fish, genotype-by-environment interaction at the level of individual gene transcription. This work contributes significantly to ongoing efforts towards documenting environmentally and sexually induced variance of gene activity and understanding the resulting phenotypes.
定量反应规范理论提出，基因型与环境互作（GxE）源于不同环境中适应性基因组合表达的个体差异。然而，实际基因组合的环境规范记录较少。在本研究中，我们通过记录养殖环境（淡水与咸水）、性别和基因型（低估计育种值EBV与高估计育种值EBV）对溪红点鲑（Salvelinus fontinalis）胰岛素样生长因子（IGF-1）和生长激素受体（GHR）转录水平的影响，研究了GxE互作对基因转录水平和生长的影响。
雄性生长速度快于雌性（微雌性符号 = 1.20 ± 0.07 g·d⁻¹，微雄性符号 = 1.46 ± 0.06 g·d⁻¹），高EBV鱼生长速度快于低EBV鱼（微低 = 0.97 ± 0.05 g·d⁻¹，微高 = 1.58 ± 0.07 g·d⁻¹；p < 0.05）。然而，咸水养殖的鱼生长速度明显低于淡水养殖的同胞（微淡水 = 1.52 ± 0.07 g·d⁻¹，微咸水 = 1.15 ± 0.06 g·d⁻¹），但咸水中GHR mRNA转录水平显著高于淡水（微咸水 = 0.85 ± 0.05，微淡水 = 0.61 ± 0.05）。实际生长与测定mRNA单位的比值（“个体转录效率”，iTE；g·d⁻¹·u⁻¹）在EBV组（微低 = 2.0 ± 0.24 g·d⁻¹·u⁻¹；微高 = 3.7 ± 0.24 g·d⁻¹·u⁻¹）和环境（微咸水 = 2.0 ± 0.25 g·d⁻¹·u⁻¹；微淡水 = 3.7 ± 0.25 g·d⁻¹·u⁻¹）间也存在差异。雄性GHR的iTE低于雌性（微雄性符号 = 2.4 ± 0.29 g·d⁻¹·u⁻¹；微雌性符号 = 3.1 ± 0.23 g·d⁻¹·u⁻¹）。环境（p > 0.7）或EBV组（p > 0.15）间IGF-1转录水平无差异，但雄性IGF-1水平是雌性的四倍（微雄性符号 = 2.4 ± 0.11，微雌性符号 = 0.58 ± 0.09；p < 0.0001）。我们检测到iTE（微雄性符号 = 1.3 ± 0.59 g·d⁻¹·u⁻¹；微雌性符号 = 3.9 ± 0.47 g·d⁻¹·u⁻¹）、盐度（微咸水 = 2.3 ± 0.52 g·d⁻¹·u⁻¹；微淡水 = 3.7 ± 0.53 g·d⁻¹·u⁻¹）和EBV组（微低 = 2.4 ± 0.49 g·d⁻¹·u⁻¹；微高 = 3.8 ± 0.49 g·d⁻¹·u⁻¹）存在显著的性别差异。检测到GHR（p = 0.027）和IGF-1（p = 0.019）以及两个基因的iTE（分别为p < 0.0001；p < 0.05）存在EBV组与环境的互作，其中咸水环境中EBV组间GHR和IGF-1转录水平差异增大。
我们的结果表明，环境和性别对生长生理途径中两个关键基因的mRNA表达均有重大影响。我们还首次证明，至少在鱼类中，个体基因转录水平存在基因型与环境互作。这项工作对记录环境和性别诱导的基因活性变异以及理解由此产生的表型的持续努力做出了重要贡献。
