Spring 2007 Asa Gray Seminars
February 26, 2007
Wei-Jen Chang, Ph.D. Assistant Professor of Biology
Department of Biochemistry and Molecular Biology, Hamilton College
"Genome Organization in Spirotrichous Ciliates (Protozoa)"
Spirotrichous ciliates undergo massive DNA elimination and genome rearrangement to construct gene-sized chromosomes in their somatic nucleus (1). An example is the extensively scrambled DNA polymerase a gene, which is broken into 48 pieces and distributed between two unlinked loci in Stylonychia (2, 3). To understand the emergence of this complex phenomenon during evolution, we examined DNA polymerase a genes in several related species, representing evolutionary intermediates. Mapping these data onto an evolutionary tree suggests that this gene became fragmented and scrambled through a series of steps, each leading to greater complexity (4). I will also discuss our recent efforts to find new scrambled genes, in addition to the three cases that have been broadly studied in the past. We have so far found three additional scrambled genes, each with novel features (5, 6). Our data suggest that 20-30% of genes in some spirotrichous ciliates may be scrambled-similar to a previous estimation. While the molecular mechanisms that scramble and unscramble genes and the evolutionary advantages/disadvantages associated with this are still largely unknown, we are making progress toward understanding this unorthodox system.
1. D. M. Prescott,Microbiol Rev 58, 233 (Jun, 1994).
2. L. F. Landweber, T. C.Kuo, E. A. Curtis, Proc Natl Acad Sci U S A 97, 3298 (Mar28, 2000).
3. D. H. Ardell, C. A.Lozupone, L. F. Landweber, Genetics 165, 1761 (Dec,2003).
4. W. J. Chang, P. D.Bryson, H. Liang, M. K. Shin, L. F. Landweber, Proc. Natl. Acad. Sci.USA 102, 15149.
5. S. Kuo, W. J. Chang,L. F. Landweber, Mol Biol Evol 23, 4 (Sep 14, 2005).
6. C. P. McFarland*, W.J. Chang*, S. Kuo, L. F. Landweber, Chromosoma 115,129.
March 26, 2007
Mark Deutschlander, Ph.D. Assistant Professor of Biology
Department of Biology, Hobart and William Smith Colleges
"The Physiological Ecology of Avian Magnetoreception"
For almost 50 years, scientists have known that birds are able to sense the earth’s magnetic field for orientation and navigation. Research has focused on elucidating the sensory receptor(s) responsible for the magnetic sense and determining the functional aspects of magnetoreception for migration. Directional choices based on the geomagnetic field depend not only on season, but also on the age and condition of birds, as well as calibration of the magnetic field with other available compass cues. Evidence suggests that birds have two different sensory systems for detection of the magnetic field: a light-dependent sense implicating the eyes in magnetoreception and a magnetite-based magnetic sense transmitted via the trigeminal nerve. Although the suggestion for more than one magnetic sense may seem far-fetched, the functional properties of these two systems are consistent with two different age-dependent uses of the magnetic field in orientation: obtaining a compass bearing and determining geographic position. Although both juvenile and adult birds possess a functional magnetic compass sense, adult birds appear to be able determine geographic position based on subtle variations in magnetic intensity and inclination. In this presentation, I will provide an overview of magnetoreception in birds with a focus on age-dependent and condition-dependent factors that affect the expression of magnetic orientation.
April 2, 2007
Gustav A. Engbretson, Ph.D. Professor and Chairman
Department of Biomedical and Chemical Engineering, Syracuse University
"Engineering New Models of Human Retinal Degenerative Disease"
Retinal degenerative diseases such as retinitis pigmentosa and macular degeneration are crippling human disorders in which the photoreceptors responsible for vision degenerate relatively slowly. Typically, a mutation in one of several rod-specific genes leads to death of the rod photoreceptors and subsequent degeneration of the cones. The reasons for the cone degeneration are not well understood. The patient progresses through night-blindness to total blindness. Though mammalian models of these degenerative diseases do exist, they all suffer from one or another shortcoming. My laboratory has been using transgenesis to develop additional models in the amphibian, Xenopus laevis. We have used the restriction enzyme mediated insertion (REMI) method to insert a variety of genes with the intent to develop frogs with “rodless” retinas in which we hope to study the interactions of rods and cones that appear to underlie the degenerative condition.
April 9, 2007
Dennis J. Stelzner, Ph.D. Professor of Cell and Developmental Biology and Medical Humanities
Department of Cell and Developmental Biology, SUNY Upstate Medical University
"It's a Jungle Out There: Approaches to Enhance Axonal Regeneration After Spinal Cord Injury"
Axonal regeneration does not occur in the central nervous system (CNS) after it is injured, although, in spite of many mistakes, regeneration does occur in the periphery. Axons of at least some neurons within the CNS are able to regenerate within peripheral nerve grafts, showing that factors in the PNS environment enhance and/or CNS environment inhibit axonal growth. These factors will be reviewed, and experiments described using two approaches attempting to promote axonal regeneration after spinal cord injury (olfactory ensheathing cell implants, and nanosphere injections of chondroitinase). It is likely that a combined approach using several therapeutic interventions will be needed to stimulate axonal regeneration leading to functional recovery.
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Susan A. Zullo'92
National Center for Human Genome Research