Li Zi-Wen, Li Xue, Yu Quan-You, Xiang Zhong-Huai, Kishino Hirohisa, Zhang Ze
The Key Sericultural Laboratory of Agricultural Ministry, Southwest University, Chongqing 400715, PR China.
BMC Evol Biol. 2009 Aug 28;9:215. doi: 10.1186/1471-2148-9-215.
Small heat shock proteins (sHSPs) are products of heat shock response and of other stress responses, and ubiquitous in all three domains of life, archaea, bacteria, and eukarya. They mainly function as molecular chaperones to protect proteins from being denatured in extreme conditions. Study on insect sHSPs could provide some insights into evolution of insects that have adapted to diverse niches in the world.
Taking advantage of the newly assembled genome sequence, we performed a genome-wide analysis of the candidate sHSP genes in the silkworm, Bombyx mori. Based on known silkworm sHSP sequences, we identified 16 silkworm sHSP genes. Most of them are distributed on two silkworm chromosomes 5 and 27, respectively. 15 of 16 silkworm sHSPs have expression evidence. The comparative analysis of insect sHSPs from B. mori, Drosophila melanogaster, Apis mellifera, Tribolium castaneum, and Anopheles gambiae revealed that there is only one orthologous cluster whereas remaining clusters are species-specific on the phylogenetic tree. This suggested that most of sHSPs might have diverged in function across insects investigated. In addition, the data presented in this study also revealed that sHSPs in the insect orthologous cluster are highly conserved in both sequence and expression pattern. In sum, insect sHSPs show a completely different evolutionary pattern from that found in vertebrate sHSPs.
B. mori has the largest number of insect sHSP genes characterized to date, including 16 genes. The inference that most species-specific sHSPs might have diverged in function across insects investigated will help us understand the adaptability of these insects to diverse environments.
小分子热休克蛋白（sHSPs）是热休克反应及其他应激反应的产物，在古菌、细菌和真核生物这三个生命域中普遍存在。它们主要作为分子伴侣发挥作用，以保护蛋白质在极端条件下不发生变性。对昆虫小分子热休克蛋白的研究有助于深入了解适应了世界上各种生态位的昆虫的进化情况。
利用新组装的基因组序列，我们对家蚕（Bombyx mori）中的候选小分子热休克蛋白基因进行了全基因组分析。基于已知的家蚕小分子热休克蛋白序列，我们鉴定出16个家蚕小分子热休克蛋白基因。其中大多数分别分布在家蚕的5号和27号两条染色体上。16个家蚕小分子热休克蛋白中有15个有表达证据。对来自家蚕、黑腹果蝇、意大利蜜蜂、赤拟谷盗和冈比亚按蚊的昆虫小分子热休克蛋白进行的比较分析表明，在系统发育树上只有一个直系同源簇，而其余的簇是物种特异性的。这表明在所研究的昆虫中，大多数小分子热休克蛋白的功能可能已经发生了分化。此外，本研究提供的数据还表明，昆虫直系同源簇中的小分子热休克蛋白在序列和表达模式上都高度保守。总之，昆虫小分子热休克蛋白呈现出与脊椎动物小分子热休克蛋白完全不同的进化模式。
家蚕拥有迄今为止已鉴定的昆虫小分子热休克蛋白基因中的最大数量，包括16个基因。关于大多数物种特异性小分子热休克蛋白的功能可能在所研究的昆虫中已经发生分化的推断，将有助于我们理解这些昆虫对不同环境的适应性。
