Comments on induction during cell differentiation

Abstract

I suspect that this symposium was convoked because many share the conviction that embryological “induction” involves mechanisms similar to those implicated in the induction of enzymes in micro-organisms. This article of faith is summarized in the axiom that anything found to be true for E. coli must also be true for elephants (Monod and Jacob, 1962). For myself, I am not sure how one compares elephants with E. coli; how, so to speak, one focuses simultaneously on both these forms. True, in both proteins may be ultimately programmed by the sequence of bases in the DNA, polysaccharides synthesized by way of uridine nucleotides and so forth, but this does not describe how the elephant, consisting of billions of individual, specialized, and generally non-dividing cells, has developed. Yet this is the crux of morphogenesis and cell differentiation — how, by way of mitotic divisions, a zygote yields so many spatially-oriented muscle, cartilage, nerve, liver and other specialized cells whose activities, when integrated, form the elephant. The problem is not primarily how a muscle cell orders smaller molecules into myosin, actin, or creatine kinase, but how one group of cells is instructed to become muscle, whereas another group, descendents from the same parent cell, is instructed to fabricate a protein-chondroitin sulphate complex and hence becomes cartilage.

This investigation was supported in part by Research Grants B-493 from the National Institute of Neurological Diseases and Blindness, United States Public Health Service, and NSF G-14123 from the National Science Foundation.

Research Career Development Awardee (U.S.P.H.S.).