美麗的蝴蝶，漂亮的七星瓢蟲(chóng),，都是人們贊美的對(duì)象,。而事實(shí)上，昆蟲(chóng)豐富的色彩,，并不僅僅是為了“好看”,。對(duì)于昆蟲(chóng)自身而言，體色和斑紋在躲避天敵,、求偶和適應(yīng)環(huán)境等方面都有重要作用,。
西南大學(xué)家蠶基因組研究團(tuán)隊(duì)利用家蠶進(jìn)行研究發(fā)現(xiàn)，昆蟲(chóng)體色的改變,，有時(shí)會(huì)非常致命,。該成果近日在國(guó)際著名學(xué)術(shù)期刊PNAS上在線發(fā)表家蠶剛孵化時(shí)形如螞蟻，故稱蟻蠶,。正常蟻蠶體色為黑色,，一種伴性赤蟻（sch，sex-linked chocolate）突變,，純合型具有巧克力色的體色,。由于該基因位于家蠶Z染色體上，所以雜合型只有雌蠶變成了巧克力色,，而雄蠶仍然為黑色,。然而，雌蠶“美麗變身”的代價(jià)十分慘重：失去了對(duì)高溫的耐受能力，遇高溫則會(huì)因不能孵化而死亡,。為何顏色的改變會(huì)帶來(lái)如此嚴(yán)重的后果,，其原因一直不明。
該團(tuán)隊(duì)劉春等通過(guò)定位克隆的方法,，對(duì)該基因分離群體進(jìn)行連鎖分析,，最后鎖定了sch突變基因所在區(qū)域。經(jīng)過(guò)努力,，最終確定了該突變?yōu)榧倚Q編碼酪氨酸羥化酶基因(Th,，tyrosine hydroxylase)調(diào)控區(qū)域突變所致：在sch突變及等位致死突變中，兩個(gè)不同類型的轉(zhuǎn)座子分別通過(guò)重組替換和插入方式破壞該基因的轉(zhuǎn)錄調(diào)控序列,，導(dǎo)致BmTh基因的表達(dá)量變化,，降低了由酪氨酸生成多巴的反應(yīng)，最終給家蠶帶來(lái)致命影響,。
該研究發(fā)現(xiàn)的酪氨酸羥化酶是位于黑色素合成途徑中的第一個(gè)關(guān)鍵酶,。黑色素與其它色素一起構(gòu)成了昆蟲(chóng)，特別是蝴蝶豐富的斑紋和體色,。劉春等人的研究還表明,，家蠶Th基因突變位點(diǎn)所在的調(diào)控區(qū)域可能具有高溫應(yīng)激功能，行使高溫刺激下增加基因表達(dá)量,，以彌補(bǔ)因高溫帶來(lái)的酶活性損失的功能,。這一結(jié)果暗示了自然界中昆蟲(chóng)體色斑紋受環(huán)境因素等影響的一個(gè)重要機(jī)制，并對(duì)人們深層次認(rèn)識(shí)昆蟲(chóng)色素功能具有重要的參考價(jià)值,。
由西南大學(xué)家蠶基因組團(tuán)隊(duì)代方銀等完成的另一個(gè)家蠶色素合成相關(guān)突變,，即家蠶暗化型（mln）突變基因的定位克隆研究，也于今年發(fā)表于JBC上,。兩篇論文都得到了國(guó)家“973”計(jì)劃等項(xiàng)目的資助,。這也是該團(tuán)隊(duì)在“發(fā)現(xiàn)基因，研究基因,，利用基因”方面的又一個(gè)重要進(jìn)展,。(生物谷Bioon.net)
西南大學(xué)近期部分研究成果
PLoS ONE：家蠶對(duì)病原菌黑胸?cái)⊙挎邨U菌侵染的分子應(yīng)答
JCB：細(xì)胞周期與原腸期胚胎模式建成之間偶聯(lián)協(xié)調(diào)分子機(jī)制
Nature Biotechnology：家蠶絲腺甲基化譜完成
生物谷推薦原文出處：
PNAS doi: 10.1073/pnas.1001725107
Repression of tyrosine hydroxylase is responsible for the sex-linked chocolate mutation of the silkworm, Bombyx mori
Chun Liua, Kimiko Yamamotob, Ting-Cai Chengc, Keiko Kadono-Okudab, Junko Narukawab, Shi-Ping Liua, Yu Hana, Ryo Futahashid, Kurako Kidokorob, Hiroaki Nodab, Isao Kobayashib, Toshiki Tamurab, Akio Ohnumae, Yutaka Bannof, Fang-Ying Daia, Zhong-Huai Xianga, Marian R. Goldsmithg, Kazuei Mitab,1, and Qing-You Xiaa,c,1
aKey Sericultural Laboratory of Agricultural Ministry, Institute of Sericulture and Systems Biology, Southwest University, Chongqing 400716, China;
bNational Institute of Agrobiological Sciences, Owashi, Tsukuba, Ibaraki 305-8634, Japan;
cInstitute of Agronomy and Life Science, Chongqing University, Chongqing 400044, China;
dResearch Institute of Genome-based Biofactory, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8566, Japan;
eInstitute of Sericulture, Ami, Ibaraki 300-0324, Japan;
fInstitute of Genetic Resources, Graduate School of Bioresource and Bioenvironmental Science, Kyushu University, Fukuoka 812-8581, Japan; and
gBiological Sciences Department, University of Rhode Island, Kingston, RI 02881
Pigmentation patterning has long interested biologists, integrating topics in ecology, development, genetics, and physiology. Wild-type neonatal larvae of the silkworm, Bombyx mori, are completely black. By contrast, the epidermis and head of larvae of the homozygous recessive sex-linked chocolate (sch) mutant are reddish brown. When incubated at 30 °C, mutants with the sch allele fail to hatch; moreover, homozygous mutants carrying the allele sch lethal (schl) do not hatch even at room temperature (25 °C). By positional cloning, we narrowed a region containing sch to 239,622 bp on chromosome 1 using 4,501 backcross (BC1) individuals. Based on expression analyses, the best sch candidate gene was shown to be tyrosine hydroxylase (BmTh). BmTh coding sequences were identical among sch, schl, and wild-type. However, in sch the ~70-kb sequence was replaced with ~4.6 kb of a Tc1-mariner type transposon located ~6 kb upstream of BmTh, and in schl, a large fragment of an L1Bm retrotransposon was inserted just in front of the transcription start site of BmTh. In both cases, we observed a drastic reduction of BmTh expression. Use of RNAi with BmTh prevented pigmentation and hatching, and feeding of a tyrosine hydroxylase inhibitor also suppressed larval pigmentation in the wild-type strain, pnd+ and in a pS (black-striped) heterozygote. Feeding L-dopa to sch neonate larvae rescued the mutant phenotype from chocolate to black. Our results indicate the BmTh gene is responsible for the sch mutation, which plays an important role in melanin synthesis producing neonatal larval color.
