Spatial mechanisms of gene regulation in metazoan embryos.
Spatial mechanisms of gene regulation in metazoan embryos.
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作者：
E. Davidson
整个后生动物的胚胎过程的基本特征被认为是重点放在那些方面，提供洞察细胞规格如何发生在发展的初始阶段。胚胎发生似乎有三种主要类型：类型1，是当今大多数无脊椎动物类群的一般形式特征，其中谱系在早期胚胎的空间组织中起重要作用，细胞特化通过自主和条件机制原位发生; 2型，脊椎动物形式的胚胎发生，其通过基本上独立于细胞谱系的机制进行，其中可扩散的形态发生素和广泛的早期细胞迁移特别重要; 3型，以长胚带昆虫为例的形式，其中几种不同的调节机制用于在细胞化之前产生核基因表达的精确模式。这些类型的胚胎发生的系统发育分布的进化意义被认为是。区域表达的同源结构域调节因子在所有三种类型的胚胎中均被利用，在后期和胚后发育中以类似的方式被利用，但在早期胚胎发育中以不同的方式被利用。这类调节器的特定下游分子功能的建议，在脊椎动物系统中获得的证据的基础上。这提供了一条途径，通过它接近基本的三种主要类型的胚胎发生的比较监管策略。
The basic characteristics of embryonic process throughout Metazoa are considered with focus on those aspects that provide insight into how cell specification occurs in the initial stages of development. There appear to be three major types of embryogenesis: Type 1, a general form characteristic of most invertebrate taxa of today, in which lineage plays an important role in the spatial organization of the early embryo, and cell specification occurs in situ, by both autonomous and conditional mechanisms; Type 2, the vertebrate form of embryogenesis, which proceeds by mechanisms that are essentially independent of cell lineage, in which diffusible morphogens and extensive early cell migration are particularly important; Type 3, the form exemplified by long germ band insects in which several different regulatory mechanisms are used to generate precise patterns of nuclear gene expression prior to cellularization. Evolutionary implications of the phylogenetic distribution of these types of embryogenesis are considered. Regionally expressed homeodomain regulators are utilized in all three types of embryo, in similar ways in later and postembryonic development, but in different ways in early embryonic development. A specific downstream molecular function for this class of regulator is proposed, based on evidence obtained in vertebrate systems. This provides a route by which to approach the comparative regulatory strategies underlying the three major types of embryogenesis.