Genetic Regulation of Ontogenesis on the Organismal Level

Abstract

As mentioned by Smalgausen (1938) “…the endocrine system is the basic integrating factor of the definite stages of morphogenesis.” The nervous system acts, in part, in the same direction. Actually, the conditions of the organism, especially the hormonal system, affect the realization of the hereditary information from the very beginning of development. The establishment of the structural-chemical organization of the ova is an example of such events. For instance, hormones stimulate protein synthesis in insect oocytes (Chapman, 1969). Hormones also induce the synthesis of yolk protein in the bird liver. This protein is later accumulated in oocytes. The corpus allatum and neurosecretory system of mosquitos produce hormones which are necessary for egg maturation (Lea, 1972). Amphibian oocytes cannot induce DNA synthesis in nuclei transplanted into them before ovulation. Such an ability is possible only after stimulation with hypophyseal hormones and the destruction of the germinal vesicle. According to Gurdon (1967) this ability, which plays a crucial role in the initiation of development, “is the result of the action of hypophyseal hormones on the mature oocytes”. It is obvious that hormonal action is a necessary condition for the occurrence of important events in the nucleus and cytoplasm of the maturating amphibian egg as well.