Thomas MacRae
George H. S. Campbell Chair in Biology
Biology
Education
1976, Ph.D. U Windsor
1973, M.Sc. U Windsor
1970, B.Sc. Mount “A”
Research Awards
- Honorary Prof, Changsha U
- FoS Killam Professorship
- U California Davis Distinguished Research Fellowship
Teaching Awards
- Dalhousie Alumni Association
Award for Excellence in Teaching - Rosemary Gill Award
- 3M Teaching Fellowship
- AAU Instructional Leadership Award
- Dalhousie U Instructional Leadership Award
- FoS Award for Excellence in Teaching
Publications
Dr. MacRae has 100 referred publications, several book chapters and other contributions, two edited books and numerous meeting abstracts and invited presentations
Website: Faculty page
Email: tmacrae@dal.ca
|
Surviving Metabolic Dormancy and Extreme Physiological Stress - Diapause
Tom MacRae was born in Halifax and grew up in New Brunswick. Upon completion of a Ph.D. and postdoctoral positions, Tom came to Dalhousie University in 1980 as a cell biologist, moving through the academic ranks and becoming Chair of the Department of Biology in 2007.
Investigation of diapause, a physiological state of dormancy characterized by extreme stress tolerance constitutes the primary research theme in my laboratory. Upon fertilization, the extremophile crustacean Artemia franciscana, employed as a model organism, can undergo diapause-destined development into encysted gastrulae (cysts). We study diapause at cell/molecular levels, including characterization of gene expression, protein structure and function, cell signalling and cytoplasmic organization. Major objectives are to understand the functional cooperation of proteins, to determine how essential cell processes are regulated and maintained and to elucidate the role of molecular chaperones in stress resistance.
Diapause Artemia embryos are remarkably indifferent to anoxia, desiccation and heat. Studying how encysted embryos survive these insults has led to the characterization of several molecular chaperones. p26, an abundant small heat shock protein produced only in diapause-destined Artemia embryos, endows transformed Escherichia coli with enhanced thermotolerance, confers stress resistance on transfected mammalian cells and inhibits apoptosis, indicating that the protein protects Artemia embryos. In ongoing work the knock down of p26 by RNAi slowed the development of diapause-destined Artemia embryos and reduced their stress tolerance. Site-directed mutagenesis and protein modelling are employed to examine the function of p26.
Subtractive hybridization, employed to investigate gene expression as Artemia embryos enter diapause, identified two additional small heat shock proteins termed ArHsp21 and ArHsp22. The elimination of ArHsp21 by RNAi has no observable phenotypic effect on diapause-destined embryos whereas most Artemia females injected with dsRNA for ArHsp22 die. The results indicate that the function of these two proteins differ from those of p26 during diapause, a proposal now under consideration.
Encysted Artemia embryos contain an abundant diapause-specific protein termed artemin which functions as a molecular chaperone. Site-directed mutagenesis and protein modelling reveal four cysteines and a hydrophobic region that influence chaperoning. Sequencing indicates that artemin has evolved from ferritin, optimizing its role as a molecular chaperone during diapause. Recent experimental results indicate that artemin is essential for the development of diapause Artemia cysts.
The molecular chaperone HSP70 appears as multiple isoforms in diapause-destined Artemia embryos. An HSP70 cDNA from Artemia is being characterized and others will be cloned in order to determine their expression during diapause-destined embryo development. Injection of females with dsRNA for HSP70 results in their death after giving birth, a unique response which carries over to the next generation of female offspring without re-injection. Sequence analysis suggests the interaction of small heat shock proteins and HSP70, perhaps part of a chaperone network that modulates proteins during diapause.
After a period of preparation following release from females, diapause in Artemia cysts is terminated by exposure to H2O2. Metabolomic and proteomic procedures are being employed to identify changes in Artemia cysts that prepare them for diapause termination and resumption of growth.
The work on molecular chaperones and diapause in Artemia has practical applications. Stably transfected mammalian cells expressing p26 and loaded with the disaccharide trehalose exhibit enhanced tolerance to drying, a finding with potential in medicine and the development of bioassays. Small heat shock proteins inhibit cataract formation in the mammalian lens and may prevent ischemia/reperfusion injury in cells during heart attack. Understanding crustacean diapause has direct significance for the commercial fishery and aquaculture where HSP70 has a role in the resistance of larval crustaceans to bacterial infection. Information derived by the study of Artemia is also applicable to diapause in insects, with economic consequences for agriculture, forestry and medicine.
|
