A Mutable Tribe

VSMC signaling, tunica media formation, and VSMC dif-fungi lay in using them, with the visible morphology of their mycelium, asexual dispersal systems, and fruiting ferentiation. The remaining five chapters of the book bodies, for studies of development. J.T. Bonner and his provide details on the formation of blood vessels in students used the slime mold Dictyostelium dicoideum selected vascular beds, including the heart, nervous to explore the aggregation of free-living amoebal cells system, kidney, lung, and placenta. This half of the book into multicellular slugs and fruiting structures. A good will be of interest primarily to specialists in the formation deal was learned of extracellular signaling among the of blood vessels in these particular organs. The chapters amoebae and the differentiation of cells within the slug, include extensive descriptions of the anatomy, cellular the stalk, and the sporangium that later formed. But the origins, and assembly of the blood vessels of each or-system was not amenable to facile genetic analysis, and gan. Most of the chapters also discuss factors that might the organism has even been cast out of the company regulate formation of these vessels, although delinea-of true fungi. But Beadle and Tatum, in their work on tion of clear functional pathways and mechanisms is Neurospora, demonstrated how biochemical pathways generally lacking. There is also substantial redundancy of simple organisms could be dissected genetically. between information on molecular mechanisms pro-Others, including Tatum himself, hoped to demonstrate vided in this portion of the book and the first half of the that developmental sequences were only slightly more book. complicated. They were frustrated by the old difficulty Despite its flaws, this book is probably the best option of tracing causal links between gene and phenotype. available for those interested in an up-to-date reference Most of the early workers disentangled themselves from on vascular development. Furthermore, the descriptive the web of cause and effect and went on to simpler and emphasis of this book and dearth of well-developed more productive lives. molecular mechanisms largely reflects our current igno-In the 1970s, the genetic analysis of the cell cycle and rance. Although hundreds of new genes with important mating system of S. cerevisiae became new inspirations functions in the vasculature have been identified, our and models for students of development, regulation, and understanding of how these genes work together to cell recognition in filamentous fungi. They have found, orchestrate the assembly of the vertebrate …