Zimmerman J L, Cohill P R
Department of Biological Sciences, University of Maryland Baltimore County 21228.
New Biol. 1991 Jul;3(7):641-50.
Although the strategies of early embryogenesis differ greatly among multicellular eukaryotes, there are certain parallels in structure, form, and function that cross even kingdom lines: the extreme heat sensitivity of zygotes and very early embryos, followed by the acquisition of thermotolerance during subsequent development, is one such parallel. The heat sensitivity may be so extreme that even moderate increases in temperature result in lethality (generally associated with the earliest phases of embryogenesis), or the effects may be less severe, resulting in defects in development but not in lethality. Mechanistically, and molecularly, these two forms of thermosensitivity appear to have different origins. On the one hand, outright lethality appears to result from an inability to induce heat shock genes and proteins; on the other hand, heat-induced developmental defects appear to result from an alteration in expression of non-heat shock genes and from a delay in the overall developmental program that generally accompanies the cell's response to heat shock. This review is focused on the developmental regulation of the heat shock response during early embryogenesis and on the impact of this regulation on the development of both animal and plant embryos. The two basic issues that we address here are (i) the expression of heat shock genes in the absence of heat shock during embryogenesis and (ii) the expression (or lack of expression) of heat shock genes after deliberate exposure of the embryos to heat shock and the consequences of this expression on its subsequent survival and development.
尽管多细胞真核生物早期胚胎发生的策略差异很大，但在结构、形态和功能上存在一些跨越界别的相似之处：合子和极早期胚胎对热极度敏感，随后在后续发育过程中获得耐热性，就是这样一种相似之处。热敏感性可能非常极端，以至于温度的适度升高都会导致死亡（通常与胚胎发生的最早阶段相关），或者影响可能不那么严重，导致发育缺陷但不会致死。从机制和分子层面来看，这两种热敏感性形式似乎有不同的起源。一方面，直接的致死性似乎是由于无法诱导热休克基因和蛋白质；另一方面，热诱导的发育缺陷似乎是由于非热休克基因表达的改变以及通常伴随细胞对热休克反应的整体发育程序的延迟。本综述聚焦于早期胚胎发生过程中热休克反应的发育调控以及这种调控对动物和植物胚胎发育的影响。我们在此探讨的两个基本问题是：（i）胚胎发生过程中在无热休克情况下热休克基因的表达；（ii）胚胎经有意热休克处理后热休克基因的表达（或不表达）以及这种表达对其后续存活和发育的影响。
