Clark Andrew G, Wang Lei
Institute of Molecular Evolutionary Genetics, Department of Biology, Pennsylvania State University, University Park, Pennsylvania, 16802.
Evolution. 1994 Aug;48(4):1230-1243. doi: 10.1111/j.1558-5646.1994.tb05308.x.
To attain balanced and efficient metabolism, the genes encoding enzymes involved in intermediary metabolism must be coordinately regulated. Gross misregulation of these genes can result in deleterious metabolic imbalances, as seen in transgenic laboratory organisms with altered gene dosage. By quantifying the expression of enzymes in nine related species of Drosophila, we hoped to see patterns of coordinated changes that could be related to evolutionary constraints on regulation. The storage pools of triacylglycerols and glycogen were measured, and the activities of 12 enzymes in intermediary metabolism were also quantified. When these phenotypes were placed on the phylogeny of the Drosophila species, quantitative cladistic hypotheses could be tested. The method of independent phylogenetic contrasts provides a formal statistical test of the null hypothesis that phenotypic changes of pairs of characters on a phylogenetic tree are independent. For example, G6PD and 6PGD exhibited a wide range of activity variation among species, and interspecific comparisons suggested significant coregulation. Significant coordinated changes among clades of the Drosophila phylogeny were also seen for 6PGD-malic enzyme, glycogen synthase-fatty acid synthase, G6PD-GPDH, and 6PGD-glycogen synthase, which in most cases exhibited positive intraspecific genetic correlation. This was to be contrasted with the relation between fatty-acid synthesis and fat storage, which exhibits a strong positive correlation within D. melanogaster but no significant interspecific correlation. Limitations of inferring evolutionary constraints by contrasting intraspecific phenotypic variation to interspecific divergence are briefly discussed.
为实现平衡且高效的新陈代谢，参与中间代谢的酶的编码基因必须受到协调调控。这些基因的严重失调会导致有害的代谢失衡，就像在基因剂量改变的转基因实验生物中所见到的那样。通过量化果蝇九个相关物种中酶的表达，我们希望能看到与调控的进化限制相关的协调变化模式。测定了三酰甘油和糖原的储存库，并对中间代谢中12种酶的活性进行了量化。当将这些表型置于果蝇物种的系统发育树上时，就可以检验定量分支假设。独立系统发育对比方法为系统发育树上成对性状的表型变化是独立的这一零假设提供了正式的统计检验。例如，葡萄糖-6-磷酸脱氢酶（G6PD）和6-磷酸葡萄糖酸脱氢酶（6PGD）在物种间表现出广泛的活性变化，种间比较表明存在显著的共调控。在果蝇系统发育的分支中，6PGD-苹果酸酶、糖原合酶-脂肪酸合酶、G6PD-甘油磷酸脱氢酶（GPDH）和6PGD-糖原合酶也出现了显著的协调变化，在大多数情况下，这些酶在种内表现出正遗传相关性。这与脂肪酸合成和脂肪储存之间的关系形成对比，脂肪酸合成和脂肪储存在黑腹果蝇内表现出强正相关，但种间无显著相关性。本文简要讨论了通过对比种内表型变异与种间差异来推断进化限制的局限性。
