Gene control of mammalian differentiation.

The differential modifications which occur in certain cells and which lead to cellular diversification are believed to be controlled by changes in gene activity. Animals which are genetic mosaics can be used to investigate the origins and consequences of differential gene action in vivo. The progress made with this experimental approach to the study of gene control of differenttion is summarized and evaluated, and ideas are suggested for future work. Major topics considered include: 1) initiation of differential gene activity in early development, 2) somites and their derivatives, 3) clonal origins of melanoblasts, 4) nervous system and sensory organs, 5) hematopoietic system, 6) sex differentiation, 7) immune system, 8) gene action in molar (teeth) development, 9) liver morphogenesis, 10) tumorigenesis, and 11) tissue-specific growth control.