Are Mammalian Regulatory Systems Simple ?
Are Mammalian Regulatory Systems Simple ?
复制标题
哺乳动物的监管系统简单吗？
作者：
A. Stewart
OHNO 1表明哺乳动物发育的分子生物学比通常想象的要简单。当然，Tfm基因变异体在研究睾酮的作用机制方面应该是卓有成效的。然而，即使接受所提出的作用方式的有效性，这种调节系统的一部分的鉴定也不能回答关于性分化的分子生物学的合理问题。它并没有告诉我们任何关于在雄性动物中诱导性腺分化为分泌睾酮而在雌性动物中不分泌睾酮的睾丸的机制的信息;但是它也没有告诉我们关于雄性和雌性动物中的特定细胞如何拥有使它们能够对睾酮产生反应的分子（Tfm蛋白1），而其他细胞则没有。同样，在那些产生Tf蛋白的细胞中，一定存在某种预先的调节，从而蛋白-睾酮复合物对编码（在Ohno的例子中）乙醇脱氢酶和β-葡萄糖醛酸酶的碱基序列的识别（无论是否涉及Ohno的纯粹假设的同源碱基序列）发生在肾近曲小管细胞中，而不是在这些酶不被诱导的睾酮的其他靶细胞中。然而，这些都是调节系统的组成部分，对性别和组织之间的分化起着至关重要的作用;不管它的作用模式是什么，睾酮只能凭借这些组成部分作为发育中转换机制的一部分。在古典胚胎学的背景下，沃丁顿在唤起和个体化之间做出了类似的区分。
OHNO1suggests that the molecular biology of development of mammals is simpler than usually supposed. Certainly, theTfmgenetic variant should prove fruitful in investigating the mechanism of action of testosterone. Even accepting the validity of the proposed mode of action, however, the identification of one part of this regulatory system does not answer questions which may legitimately be asked about the molecular biology of sexual differentiation. It is not claimed that it tells us anything about the mechanism which induces the gonad to differentiate as a testis secreting testosterone in male animals but not in females; but neither does it give us any information as to how particular cells in both male and female animals come to possess the molecule (theTfmprotein1) which enables them to respond to testosterone, whereas other cells do not. Again, among those cells which do produce theTfmprotein, there must be some prior regulation whereby the recognition of base sequences coding (in Ohno's example) for alcohol dehydrogenase and β-glucuronidase by the protein–testosterone complex (whether or not this involves Ohno's purely hypothetical homologous base sequences) occurs in kidney proximal tubule cells, but not in other target cells of testosterone where these enzymes are not induced. Yet these are the components of the regulatory system crucially responsible for differentiation between sexes and between tissues; whatever its mode of action may be, testosterone can only act as part of a switching mechanism in development by virtue of such components. In the context of classical embryology, Waddington has made a similar distinction between evocation and individuation2.