家蚕狭胸(narrow breast,nb)突变性状观察及基因的精细定位

The observation of phenotype and the fine mapping of narrow breast mutant of silkworm, Bombyx mori

狭胸(narrow breast,nb)是家蚕少数几个体型突变种之一,其表型为胸部狭小,位于19号染色体的31.2位点,该突变为自然隐性突变。到目前为止,其突变基因还未被分离克隆,突变机理未知。为了分离克隆nb的突变基因,阐释其突变机理,本研究首先对nb蚕的突变性状进行观察。发现3龄时,nb狭胸表型开始明显,并维持到蛹期。5龄期的nb与野生型的体重没有明显差异,但nb体长明显的比正常表型短。5龄5d解剖观察发现nb和野生型个体前肠存在差异,nb前肠在食道处收缩,而正常个体是逐渐变大且呈漏斗状。同时,本研究还采用大造和nb为亲本构建BC_1群体,通过筛选合适的SNP标记对nb突变基因进行了精细定位,其结果为:利用10 SNP个标记和92个BC_1代个体进行连锁分析,将nb突变相关基因位于标记3和8之间的区域内,遗传距离为7.8cM,物理距离约为1.7Mb。利用13个可用于定位的标记和1794个BC_1代个体,nb突变基因位于标记31和38之间区域内,该区域物理跨度约为1Mb,基因预测结果显示定位区域内含有44个基因。本研究为nb突变基因的定位及机理的阐释提供了参考信息。

narrow breast(nb)is one of the rare mutant species relating to the body shape.The mutant presents narrowed breast phenotype caused by recessive natural mutant by single gene which located on the 31.2 locus of the 19^th linkage group.However,up to now,the correspond gene has not been isolated and cloned,and the mechanism is unknown.With the purpose to clone the mutant gene and reveal the mechanism,the mutant phenotype of nb was observed at first.The character of nb mutant strain started to present gradually from the later period of 3^th instar,and it became more and more clearly and kept until pupae stage.Besides,it was no difference in the weight between the nb mutant strain and the normal one,however,the body length of the nb mutant strain is dramatically shorter than the normal one.Some differences in the frontier gut was observed between the normal and nb mutant strain on the fifth day in 5^th instar according to the dissection observation.There was a narrow region at the esophagus in the nb mutant strain,but presented a funnel shape with a gradual increase in the normal strain.We used Dazao and nb as the parental strains to produce the population of BC1 generation for positonal cloning.10 SNP markers could use for mapping after screening.By using these markers and 92 BC1 individuals,we constructed a low-density linkage map of nb.The nb linked region was narrowed to the 1.7Mb range on chromosome 19 between two SNP markers 3 and 8.The genetic distance between the two markers is 7.8cM.With another 13 SNP markers and 1794 BC1 individuals,the nb linked region was further narrowed to the 1Mb range between two SNP markers,31 and 38.It contains 44 prediction genes among the positioning area.This study provides reference information for the positioning of the nb and interpretation of the mechanism.