symmetry out, asymmetry in对称,不对称.pdf

Symmetry 2010, 2, 1033-1054; doi:10.3390/sym2021033 OPEN ACCESS symmetry ISSN 2073-8994 /journal/symmetry Review Symmetry OUT, Asymmetry IN Raquel Lourenço 1,2 and Leonor Saúde 1,2,* 1 Instituto de Medicina Molecular e Instituto de Histologia e Biologia do Desenvolvimento, Faculdade de Medicina da Universidade de Lisboa, Portugal; E-Mail: ralourenco@fm.ul.pt 2 Instituto Gulbenkian de Ciência, Oeiras, Portugal * Author to whom correspondence should be addressed; E-Mail: msaude@fm.ul.pt. Received: 15 March 2010; in revised form: 23 April 2010 / Accepted: 18 May 2010 / Published: 25 May 2010 Abstract: The formation of a perfect vertebrate body plan poses many questions that thrill developmental biologists. Special attention has been given to the symmetric segmental patterning that allows the formation of the vertebrae and skeletal muscles. These segmented structures derive from bilaterally symmetric units called somites, which are formed under the control of a segmentation clock. At the same time that these symmetric units are being formed, asymmetric signals are establishing laterality in nearby embryonic tissues, allowing the asymmetric placement of the internal organs. More recently, a “shield” that protects symmetric segmentation from the influence of laterality cues was uncovered. Here we review the mechanisms that control symmetric versus asymmetric development along the left-right axis among vertebrates. We a