Jean Brachet Memorial Lecture to the ninth international conference of the International Society of Differentiation: Genomic potential—Acetabularia to mammals

Abstract

It is indeed a distinct honor and pleasure for me to nuclear transplants. Later, Danielli (5,6) and colleagues produced clonal lines of nucleocytoplasmic hydeliver the 1996 Jean Brachet Memorial Lecture because his research profoundly influenced Develop-brid Amebae to study the relative importance of cytoplasmic inheritance in contrast to nuclear inheritance. mental Biology. Among his prolific and varied investigations extending from oogenesis to organogenesis, Some phenotypic characteristics were found to be controlled exclusively by the nucleus (free amino acid comBrachet contributed to our knowledge of nucleocytoplasmic interactions in Acetabularia, Ameba, sea ur-position, cytoplasmic crystals, length of cell cycle), whereas several were influenced by both the nucleus chins, and amphibia. It is in the field of nucleocytoplasmic interactions that I have worked and is the subject and the cytoplasm (nuclear diameter, normal shape, resistance to different chemicals, response to different of this paper. Specifically, I shall review the genomic potential of cells revealed through nuclear transplanta-antisera). Nuclear transfers in Ameba combined with autoradiography (7) demonstrated that RNAs are syntion experiments in somatic cells of Acetabularia, Ameba, and Stentor, and in the oocytes of Drosophila, thesized in the nucleus and move to the cytoplasm, whereas proteins are synthesized in the cytoplasm. In fish, amphibia, and mammals.addition, some RNA and protein species shuttle be-ACETABULARIA, AMEBA, AND STENTOR tween the cytoplasm and nucleus, and the cytoplasm exerts a major control on mitosis and DNA synthesis. The first successful recombination of nucleus and cy-Nuclear transplants and grafting experiments in the toplasm was performed by Hä mmerling (1) in the giant unicellular Stentor revealed cytoplasmic inheritance of unicellular green plant, Acetabularia, by means of cortical pattern in the formation of mouthparts (8) and, grafting experiments. The plant consists of three main as in Ameba, the cytoplasm controls macronuclear DNA parts: the rhizoid at the basal end containing the so-synthesis (9). matic nucleus, the stalk, and at the apical end, theThe innovative experiments with unicellular organumbrella expressing the species phenotype. Hä m-isms, though predating molecular biology, predicted merling (1) found that not only could anucleated frag-important molecular principles concerning the sites of ments of the stalk regenerate umbrellas, but more sur-RNA and protein synthesis, their translocation within prisingly, fragments farthest removed from the nucleus the cell, and the stability of some RNA species. Equally regenerated the best umbrellas. This finding suggested important, nuclear transfers in unicellular organisms that the stalk contained morphogenetic substances dis-provided a conceptual plan for the future analysis of tributed along a linear gradient in which the concentra-the genomic potential of metazoan cells and the cloning tion was lowest at the basal end near the nucleus, and of multicellu...