Part Four - Molecular Biology: The Genome in Action 331

19. Differential Gene Expression in Development 426

19.1 What Are the Processes of Development? 427 Development proceeds via determination, differentiation, morphogenesis, and growth 427 Cell fates become more and more restricted 428 19.2 Is Cell Differentiation Irreversible? 429 Plant cells are usually totipotent 429 Among animals, the cells of early embryos are totipotent 430 The somatic cells of adult animals retain the complete genome 431 Pluripotent stem cells can be induced to differentiate by environmental signals 432 Embryonic stem cells are potentially powerful therapeutic agents 433 19.3 What Is the Role of Gene Expression in Cell Differentiation? 435 Differential gene transcription is a hallmark of cell differentiation 435 Tools of molecular biology are used to investigate development 435 19.4 How Is Cell Fate Determined? 436 Cytoplasmic segregation can determine polarity and cell fate 436 Inducers passing from one cell to another can determine cell fates 437 19.5 How Does Gene Expression Determine Pattern Formation? 439 Some genes determine programmed cell death during development 439 Plants have organ identity genes 440 Morphogen gradients provide positional information 441 In the fruit fly, a cascade of transcription factors establishes body segmentation 442 Homeobox-containing genes encode transcription factors 445