蜗壳螺旋的手性（即镜像不能叠加的一种结构）由一个单一位点在遗传上决定，是由母方遗传的。对此负责的基因一直未被发现。
Reiko. Kuroda等人发现，对大蜗牛“静水椎实螺”（Lymnaea stagnalis）8-细胞阶段的胚胎中的细胞进行简单的操纵，能够在成年个体中逆转手性。而且引人注目的是，nodal基因（一个在很多物种中赋予左-右非对称性的基因）的表达也被细胞的重排逆转。他们还发现，在手性决定基因（一个或多个）与在促进主导型分裂球排列的第三次分裂时的手性细胞骨架动态之间有一个强烈的基因联系。这一可以跟踪的实验体系的获得，将使左-右对称性的机制比以前更容易研究。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 462, 790-794 (10 December 2009) | doi:10.1038/nature08597
Chiral blastomere arrangement dictates zygotic left–right asymmetry pathway in snails
Reiko Kuroda1,2,3, Bunshiro Endo2, Masanori Abe2 & Miho Shimizu2
1 Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan
2 Kuroda Chiromorphology Team, ERATO-SORST, JST, Komaba, Meguro-ku, Tokyo 153-0041, Japan
3 Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
4 Correspondence to: Reiko Kuroda1,2,3 Correspondence and requests for materials should be addressed to R.K.
Most animals display internal and/or external left–right asymmetry. Several mechanisms for left–right asymmetry determination have been proposed for vertebrates1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and invertebrates1, 2, 4, 9, 11, 12, 13, 14 but they are still not well characterized, particularly at the early developmental stage. The gastropods Lymnaea stagnalis and the closely related Lymnaea peregra have both the sinistral (recessive) and the dextral (dominant) snails within a species and the chirality is hereditary, determined by a single locus that functions maternally15, 16, 17, 18. Intriguingly, the handedness-determining gene(s) and the mechanisms are not yet identified. Here we show that in L. stagnalis, the chiral blastomere arrangement at the eight-cell stage (but not the two- or four-cell stage) determines the left–right asymmetry throughout the developmental programme, and acts upstream of the Nodal signalling pathway. Thus, we could demonstrate that mechanical micromanipulation of the third cleavage chirality (from the four- to the eight-cell stage) leads to reversal of embryonic handedness. These manipulated embryos grew to ‘dextralized’ sinistral and ‘sinistralized’ dextral snails—that is, normal healthy fertile organisms with all the usual left–right asymmetries reversed to that encoded by the mothers’ genetic information. Moreover, manipulation reversed the embryonic nodal expression patterns. Using backcrossed F7 congenic animals, we could demonstrate a strong genetic linkage between the handedness-determining gene(s) and the chiral cytoskeletal dynamics at the third cleavage that promotes the dominant-type blastomere arrangement. These results establish the crucial importance of the maternally determined blastomere arrangement at the eight-cell stage in dictating zygotic signalling pathways in the organismal chiromorphogenesis. Similar chiral blastomere configuration mechanisms may also operate upstream of the Nodal pathway in left–right patterning of deuterostomes/vertebrates.
