Kammermeier L, Reichert H
Institute of Zoology, University of Basel, Basel, Switzerland.
Brain Res Bull. 2001 Aug;55(6):675-82. doi: 10.1016/s0361-9230(01)00559-7.
Recent genetic studies on embryonic brain development in the fly Drosophila melanogaster together with investigations on early morphogenesis and patterning in the embryonic brain of the mouse revealed developmental mechanisms that are strikingly similar in insects and mammals. The homeotic (Hox) genes are expressed in a virtually colinear anteroposterior pattern in the developing posterior brain of insects and mammals, where they are required for the specification of segmental neuronal identity. The otd/Otx cephalic gap genes are expressed in the anterior brain of insects and mammals and are of central importance for its formation because in both phyla loss of otd/Otx2 causes the loss of the entire rostral brain. Specific Pax genes are involved in numerous aspects of brain development in both phyla. These developmental genetic findings reveal a striking evolutionary conservation of cephalic gap gene, homeotic gene, and Pax gene action in embryonic brain development that extends beyond gene structure to encompass patterned expression and function. This comparative evidence indicates that the genetic programs which direct embryonic brain development are remarkably conserved and lends further support to the hypothesis that a common molecular bauplan underlies brain development in invertebrates and vertebrates. In consequence, it seems increasingly likely that both modern brain types share their evolutionary origin in a common ancestral bilaterian brain which was established before the protostome-deuterostome divergence over 600 million years ago.
近期对果蝇胚胎脑发育的遗传学研究，以及对小鼠胚胎脑早期形态发生和模式形成的研究表明，昆虫和哺乳动物的发育机制惊人地相似。同源异型（Hox）基因在昆虫和哺乳动物发育中的后脑以几乎共线性的前后模式表达，在那里它们是确定节段性神经元身份所必需的。otd/Otx头部间隙基因在昆虫和哺乳动物的前脑表达，对其形成至关重要，因为在这两个门类中，otd/Otx2的缺失都会导致整个 Rostral 脑的缺失。特定的Pax基因在这两个门类的脑发育的许多方面都有涉及。这些发育遗传学发现揭示了头部间隙基因、同源异型基因和Pax基因在胚胎脑发育中的作用具有惊人的进化保守性，这种保守性不仅延伸到基因结构，还包括模式化表达和功能。这一比较证据表明，指导胚胎脑发育的遗传程序非常保守，并进一步支持了这样一种假设，即共同的分子蓝图是无脊椎动物和脊椎动物脑发育的基础。因此，现代的两种脑型似乎越来越有可能在一个共同的祖先双侧对称脑中有共同的进化起源，这个共同的祖先双侧对称脑是在6亿多年前原口动物 - 后口动物分化之前就已形成的。
