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Biology of Developmental Transcription Control. Conference proceedings. Irvine, California, October 26-28, 1995

1996; National Academy of Sciences; Volume: 93; Issue: 18 Linguagem: Inglês

10.1073/pnas.93.18.9307

1091-6490

Eric H. Davidson,

Developmental Biology and Gene Regulation

The theme of this Colloquium was the core set of mechanisms that underlie the phenomenon of development. We are learning how genomic control of differential gene expression works in developmental space and time. The Colloquium focused on gene regulatory mechanisms that control spatial gene expression during embryonic development and in postembryonic morphogenesis; on signal-mediated changes in cell fate; and on genomic organization and chromatin configuration as these affect developmental gene expression. Session I of the Colloquium was entitled Control of in Embryos. At the beginning of development, the nuclei of all the embryonic blastomeres are naive, in that they have no previous history of differential gene expression, unlike cell lineages of the postembryonic organism. The mechanisms by which embryonic nuclei attain specific patterns of gene expression were the subject of Session I, which was chaired by Michael Levine. His paper, which is included in the following collection, illuminates mechanisms of transcriptional repression that set the boundaries of the spatial domains of gene expression in Drosophila embryos. The second paper in the collection, also from Session I, is by Noriyuki Satoh, with I. Araki and Y. Satou. Their work demonstrates the autonomous specification of muscle lineages and the transcriptional activation of muscle genes in ascidian embryos, which are of particular interest as the simplest surviving invertebrate chordates. The third paper in the collection, by C. V. Kirchhamer, C.-H. Yuh, and Eric Davidson, is focused on the modular functional organization of the cis-regulatory systems that control spatial expression of two genes that are territorially active in the early sea urchin embryo. Session I of the Colloquium also included a presentation by Robert Goldberg on spatial control of gene expression in embryos of a higher plant and a presentation by J. C. Smith that dealt with the developmental role of the transcription factor encoded by the amphibian Brachyury gene and embryonic control of its expression by upstream signaling systems. Session II was entitled Signaling and Specification of Cell Type. The papers in this session centered on the molecular mechanisms by which intercellular signals causally specify developmental cell fates. A series of known signaling interactions sets the various cell fates executed in the development of the Caenorhabditis elegans vulva, and the stepwise process which then leads to the fusion of regionally differentiated uterine and vulval epithelia is described in the paper of A. Newman and Paul Sternberg, which is included in this collection. John Gurdon's paper with A. Mitchell and K. Ryan then addresses the range over which cell signaling affects mesoderm specification in Xenopus embryos. Session II also included presentations by Mariann Bienz, who served as Chair of the session, on signaling interactions upstream of the Ubx gene in Drosophila midgut differentiation; by Scott Fraser, -on cell type specification in zebrafish embryos, as revealed by the in vivo imaging of labeled blastomere clones; and by Gerry Rubin, who discussed signaling pathways that affect cell fate specification in the developing Drosophila eye. This specification pathway can now be traversed all the way from ligand to transcription factors that lie at the termini of the signal transduction pathways. Session III of the Colloquium was entitled Expression and Spatial Organization of Morphogenesis. This session concerned complex pattern formation processes in the morphogenesis of particular vertebrates and insect structures. The session was chaired by Rob Krumlauf, whose paper with S. Nonchev, M. Maconochie, C. Vesque, S. Aparicio, L. ArizaMcNaughton, M. Manzanares, K. Maruthainar, A. Kuroiwa, S. Brenner, and P. Charnay demonstrates a remarkably conserved, pan-vertebrate regulatory circuit. Their study demonstrates that the Krox-20 transcription factor controls expression of certain Hox genes, in rhombomeres 3 and 5 of the hindbrain, from fish to mammals. The next paper, by V. Marigo and Cliff Tabin, identifies an essential downstream target of the important hedgehog signaling ligand in the developing neural tube. This is the gene patched, expression of which is activated in response to hedgehog signaling, and the product of which is a negative regulator in the signaling pathway. A paper of M. Selleck and Marianne Bronner-Fraser next describes microsurgical experiments that demonstrate the inductive specification of neural crest cells in the neural tube, by adjacent dorsal ectoderm. Session III also included presentations by Sean Carroll on the regulation of the vestigial gene, which encodes a transcription factor controlling patterning and growth of the insect wing; and by James W. Posakony, who described a genetic and transgenic expression analysis of the molecular process by which elements of the Drosophila peripheral nervous system are positioned, specified, and cellularly organized. Session IV was entitled Transcription Factor Interactions in Control of Differentially Expressed Genes. These presentations concerned mechanisms of interaction amongst transcription factors bound within given cis-regulatory systems that result in positive or negative regulatory output. The present collection includes two papers from Session IV. The first, by Ellen Rothenberg and S. B. Ward, demonstrates that the IL-2 gene is regulated by coordinate assembly of a complex of diverse transcription factors on the cis-regulatory domain of the gene. The second paper, by J. D. Molkentin and Eric Olson, describes combinatorial functions of basic helix-loophelix and MADS-box transcription factors in the developmental activation of muscle-specific genes. Other presentations in Session IV were by Tom Maniatis, who served as Chair and who described the complex regulation of assembly and degradation of the IKB transcription factor complex; by Sandy Johnson, who spoke about molecular mechanisms of transcriptional repression in yeast; and by Keith Yamamoto, who discussed multiple regulatory interactions that affect the transcriptional control functions of the glucocorticoid receptors. Session V was entitled Insertion Elements, Organization of Gene Families, and Gene Expression. Papers presented in the first part of this session concerned transposable elements and their roles in the evolution of regulatory functions. The session Chair was Roy Britten, whose paper on evolutionarily mobile