蜗牛壳的手性（卷绕的方向）是生物学上的一个长期未解之谜。现在Cristina Grande和 Nipam Patel发现，蜗牛手性是由一个以其在脊椎动物左-右非对称性中的作用而知名的基因调控的，该基因的名称为“nodal”。
多数动物是两侧对称的，但在这一框架内却表现出不同程度的左-右非对称性。在脊椎动物和其他后口动物中，导致非对称性的分子通道会利用信号作用分子Nodal。Grande 和Patel在两个蜗牛物种中发现了Nodal的直系同源物（演化上的对应物）及其目标之一Pitx，还发现Nodal的失去会中断蜗牛壳的卷绕。这表明，“nodal”信号通道对所有两侧对称动物都是原始的，并不像人们曾经怀疑的那样是后口动物所特有的。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 457, 1007-1011 (19 February 2009) | doi:10.1038/nature07603
Nodal signalling is involved in left–right asymmetry in snails
Cristina Grande1,2,3 & Nipam H. Patel1,2,3
1 Department of Molecular and Cell Biology,
2 Department of Integrative Biology, and,
3 Center for Integrative Genomics, University of California, Berkeley, California 94720-3200, USA
Many animals display specific internal or external features with left–right asymmetry. In vertebrates, the molecular pathway that leads to this asymmetry uses the signalling molecule Nodal, a member of the transforming growth factor-β superfamily1, which is expressed in the left lateral plate mesoderm2, and loss of nodal function produces a randomization of the left–right asymmetry of visceral organs3, 4. Orthologues of nodal have also been described in other deuterostomes, including ascidians and sea urchins5, 6, but no nodal orthologue has been reported in the other two main clades of Bilateria: Ecdysozoa (including flies and nematodes) and Lophotrochozoa (including snails and annelids). Here we report the first evidence for a nodal orthologue in a non-deuterostome group. We isolated nodal and Pitx (one of the targets of Nodal signalling) in two species of snails and found that the side of the embryo that expresses nodal and Pitx is related to body chirality: both genes are expressed on the right side of the embryo in the dextral (right-handed) species Lottia gigantea and on the left side in the sinistral (left-handed) species Biomphalaria glabrata. We pharmacologically inhibited the Nodal pathway and found that nodal acts upstream of Pitx, and that some treated animals developed with a loss of shell chirality. These results indicate that the involvement of the Nodal pathway in left–right asymmetry might have been an ancestral feature of the Bilateria.
