Developmental expression and modification of genes

Differentiating tissue is characterized by a specific repertoire of proteins out of whichsome are developmentally controlled. This review describes modifications in the structureof genes which encode developmentally regulated proteins. Evidence is provided for changes in chromatin conformation and DNA méthylation of specific genes -either change can be observed in various stages of some vertebrates. The involvement of hormones in regulatingDNA modifications is suggested, and interrelationships between DNA modifications and geneexpression are discussed.Dramatic metabolic changes, which prepare the organism for independent life, occur in the perinatal period of mammals. For instance, gluconeogenesis commences upon birth after the abrupt cessation of glucose supply from the mother [1], Likewise, uro-genesis or the synthesis of lung surfactant start in the perinatal period [2, 3]. These functions are in fact the end products of developmental processes which involve the synthesis of a new repertoire of proteins leading to maturation of organs [4]. To further understand the mechanisms controlling development, one should explore the early events which are directly involved in the initiation of synthesis of proteins. Recent evidenceby Powell et al. [5] implies that initiation of transcription of the genes which encode tissue-specific proteins is a major control mechanism in the development of a tissue [5]. This suggests that the synthesis of developmentally regulated proteins is a direct consequence of the initiation of the transcription of these genes.