编者按：这是一个很有趣的科学问题，为什么高等生物器官，尤其是脊椎生物会出现左右器官不对称，今天刚刚出版的Nature报道了这个发现。以前的研究认为Notch信号中的Nodal 基因和胞浆内自由钙是主要决定因素，最新的研究显示细胞外钙也是重要的因素，它能被Notch信号感受，并表达不同的基因。象为什么大象大而狗小，为什么有些动物能在水中进行肺呼吸而不缺氧...，这一系列看似简单的平常问题，都包含有许多科学道理。
Learning right from left
A central unanswered question in vertebrate embryology is how the initial symmetry of the embryo is broken, and left—right organ asymmetry established. This important step in the development of the body plan is known to involve the Notch signalling pathway, which regulates expression of the Nodal gene. A mathematical model has now been used to identify factors regulating Notch during chick embryo gastrulation. This leads to the identification of transient localized accumulation of extracelluar calcium ions as the source of asymmetric activation of Notch. Free cytosolic Ca2+ is important throughout embryonic development. This latest finding suggests that extracellular Ca2+ is also important, sensed by Notch and translated into differential gene expression.
Notch activity acts as a sensor for extracellular calcium during vertebrate left-right determination
ÁNGEL RAYA, YASUHIKO KAWAKAMI, CONCEPCIÓN RODRÍGUEZ-ESTEBAN, MARTA IBAÑES, DIEGO RASSKIN-GUTMAN, JOAQUÍN RODRÍGUEZ-LEÓN, DIRK BÜSCHER, JOSÉ A. FEIJÓ & JUAN CARLOS IZPISÚA BELMONTE
Nature 427, 121–128 (2004); doi:10.1038/nature02190
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Developmental biology: Asymmetric fixation
NICK MONK
Computer simulations and laboratory experiments have shed light on how an asymmetric pattern of gene expression is fixed in vertebrate embryos — an early step towards asymmetric development of the internal organs.
Nature 427, 111–112 (2004); doi:10.1038/427111a
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