Norman Davidson - US grants

High resolution mapping of single copy genes on mammalian metaphase chromosomes will be accomplished by in situ hybridization and transmission electron microscopy. The proposed technique is based on that developed for polytene chromosome (Wu, M. and Davidson, N. (1981), Proc. Natl. Acad. Sci. 79, 7059-7083). As electron opaque labels colloidal gold spheres with diameters in the range of 25 nm are used. The spheres are coated with a layer of protein to which E. coli single stranded DNA is photochemically cross-linked. Poly (dA) tails are added to the 3 feet OH ends of a fragmented cloned DNA molecule, corresponding to the gene of interest. These probe-dA strands are hybridized in situ to metaphase chromosome spreads. Gold spheres are linked to the hybridized probe-dA stands by A:T base pairing. The sphere positions relative to the chromosome bands can be observed by transmission electron microscopy. The methods shows low background and high resolution. Genes to be mapped include the repeated ribsomal RNA genes and histone genes, globin genes, immunoglobulins, and histocompatibility genes, on the chromosomes of mice and men.

The overall goals are to understand the molecular basis at the DNA sequence level for the developmental regulation of gene expression. In particular, we wish to understand the structure and the expression of the genes coding for the proteins that make up muscle fibers. Genes for a number of such proteins - actin, myosin heavy chains, myosin light chains, tropomyosin, and others - are all switched on to a high level of expression when myogenic cells undergo the myoblast to myotube differentiation step. It is proposed to characterize these muscle protein genes of the fruit fly, Drosophila. In Drosophila, these genes constitute a defined limited system for which it will be possible to obtain a relatively complete description; furthermore, in Drosophila it is possible to correlate genetic data on mutants defective in muscle function with the physical structures of the genes. It is proposed to study the DNA function with the physical structures of the genes. It is proposed to study the DNA sequences in regions around the genes which are necessary for the developmental switches in excpression by reintroducing cloned vertebrate muscle protein genes back into the chromosomes of mammalian myogenic cells in culture, and studying the switches in expression of these cloned genes when the cells are induced to undergo the myoblast to myotube differentiation step. It is further proposed to clone and characterize the genes that code for the acetyl choline receptors which occur at nerve-muscle synapses. This system is an excellent example of a multi-subunit membrane bound complex at the cell surface which responds to an external molecular signal. The appropriate system for these studies are the receptor genes that are abundantly expressed in the electric organ of the ray, Torpedo californica. These studies will provide a deeper understanding of developmental diseases in general and of myasthenia gravis and of muscular dystrophy.

health science research support; health /scientific organization;

It is important to know whether hemispheric asymmetries in cognitive processing are unique to human intelligence and consciousness or whether they represent more fundamental vertebrate adaptations. Moreover, if other animals do have human-like lateralization then the possibility exists of studying the neural mechanisms of hemispheric specialization with many modern techniques not appropriate for human experiments. In addition, cognitive and structural models of laterality may be evaluated meaningfully with data from animals as well as from human beings. Such research should have profound effects for understanding a variety of diseases, such as dyslexia, immune disorders, psychiatric disturbances, and hormonal imbalances, that are now being associated with atypical lateralization of the brain. Rhesus monkeys are being studied to see whether their left and right hemispheres differ in cognitive processing as do the hemispheres of human beings. This is done by independently testing the separated hemispheres of split-brain monkeys on a variety of visual discriminations that are known to show lateralized processing in human subjects. Key features of the discriminations are manipulated and the effects on lateralization noted. Such effects also are looked for when split-brain patients perform similar discriminations, allowing the similarity of hemispheric specialization in both species to be assessed. For example, it appears that both split-brain monkeys and human beings process facial information better with the right cerebral hemisphere than with the left. The effects of inverting facial stimuli on recognition are being studied because they permit specific models of facial processing to be tested. Once laterality has been measured for a variety of tasks, it should be possible to see how well performance in different tasks correlates, and then to infer if lateralization of function arises from fundamental hemispheric differences.

biomedical equipment purchase;