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Scientist: London Regional Cancer Program, London Health Sciences Centre, London, Ontario
Associate Professor: Department of Oncology, University of Western Ontario, London, Ontario
Cross Appointments: Department of Biochemistry
London Regional Cancer Program
Room 4066, Cancer Research Laboratory Program
790 Commissioners Rd. E.
Canada N6A 4L6
Undergraduate Student:Ruth Atoshim Fessahaye, Department of Biochemistry
Major laboratory interests involve studies of molecular mechanisms that regulate cell differentiation. Our main focus is to identify and characterize genes that regulate muscle development, or myogenesis, in the early developing mouse embryo. Skeletal muscle originates from somites which are derived from mesodermal epithelial cells flanking the neural tube, and mature somites are organized into three different compartments consisting of the dermatome, myotome, and sclerotome. Cells from these three compartments will subsequently migrate to different regions of the developing mouse and differentiate into cells that form the dermis, muscle and axial skeleton, respectively.
Embryonic cells possess the potential to differentiate and become more committed to specialized cell types as they divide. This process requires a highly regulated mechanism. When this mechanism is deregulated, cells will lose their ability to differentiate or undergo de-differentiation and will divide without any control. These cells could then become malignant and lead to cancer. We wish to learn about the molecular mechanism underlying normal cellular differentiation and embryonic development, and this will help us understand the events leading to neoplasia.
Malignant and embryonic cells share many similarities, and the process of carcinogenesis is generally considered to reflect a de-differentiation of mature cells or the abnormal differentiation of stem cells, such as those in the bone marrow. To learn more about the events leading to neoplasia, it is necessary to understand the molecular mechanism underlying cellular differentiation during embryonic development.
The development of the mammalian embryo requires a highly regulated mechanism to organize and establish a specific body plan; to define different cell lineages and cell fate; to control cell growth and migration, as well as the terminal differentiation of cells with a defined function and morphology. These events take place in an orderly fashion and require the expression and/or inactivation of specific regulatory genes in a precise spatial and temporal pattern during embryogenesis.
The major interests of my laboratory involve studies of molecular mechanisms that regulate cell differentiation. Our main focus is to identify and characterize genes that regulate muscle development, or myogenesis, in the early developing mouse embryo. Skeletal muscle originates from somites which are derived from mesodermal epithelial cells flanking the neural tube, and mature somites are organized into three different compartments consisting of the dermatome, myotome, and sclerotome. Cells from these three compartments will subsequently migrate to different regions of the developing mouse and differentiate into cells that form the dermis, muscle and axial skeleton, respectively.
Regulation of myogenesis in the early mouse embryo
Muscle differentiation represents an important paradigm for studies of how different cell lineages are established during development in mammals because: (1) the morphological change from individual myoblasts to multinucleated myotubes during differentiation can be followed histologically, and this makes it possible to identify rare events that influence differentiation; (2) the differentiation event is well defined by the expression of muscle-specific markers, for which antibodies and molecular probes are readily available; (3) differentiation can be initiated in many myogenic cell lines that are amenable to experimental manipulations, and (4) terminal differentiation of muscle cells require the interaction of other tissues and responses to environmental cues. This system will therefore allow us to discriminate between factors important for autonomous cellular differentiation and those arising from cell and/or tissue interactions.
The identification of a family of myogenic regulatory genes has greatly advanced our understanding of the molecular events that activate myogenesis. This gene family consists of four members, including; myf-5, myogenin, myoD and mrf-4. They are considered as "master regulatory genes" because of their remarkable ability to activate the expression of muscle-specific genes, and because they can impose muscle phenotypes on many different cell types. These myogenic factors are all transcription factors which share structural homology and biological activities. However, each of them exhibits a distinct temporal expression profile during embryogenesis, and this suggests that they have different roles in the expression of myogenic genes. In essence, they are important to cell fate determination and the activation of myogenesis during development.
To understand the processes of myogenesis it will be necessary to elucidate: (1) the processes by which cells in newly formed somites become committed to the myogenic lineage, and (2) the ways in which genes that encode proteins of the contractile apparatus are subsequently activated. To this end, we are investigating the regulation of master regulatory genes in somites and their modes of action during embryogenesis using transgenic mice. As a prelude to these studies, I have previously identified the minimum myogenin promoter sequence that is able to faithfully recapitulate its spatiotemporal expression in developing mice and have also initiated studies to characterize the cis-acting regulatory sequences of myf5.
Our aims are now to:
Skeletal development during early mouse development
During our transgenic studies we have isolated an insertional mouse mutant with skeletal abnormalities. The mutant mice display a severe kinked tail and have also developed kyposcoliosis (severe curvature of the spine), and we have designated the gene associated with these skeletal abnormalities as kkt for "kypgscoliosis kinked tail". The skeletal abnormalities observed in the kkt mice is similar to the Pax1 mouse mutant, undulated. Pax1 is a transcription factor that plays an important role in skeletal development. It has also been shown that over-expression of Pax1 can convert normal cells into malignant cells in culture. Our molecular analyses show that the structure and expression of the Pax1 gene in the kkt mice is identical to wild-type animal. We have isolated a partial cDNA within the kkt locus, and sequence analysis shows that this is a novel gene that has not been described previously, and our analysis reveal that kkt is located at the proximal end of chromosome 2 adjacent to the Pax1 locus. Our preliminary results show that kkt plays an important role in skeletal development. We are now in the process to identify the full length cDNA of kkt and we will determine the functional role of kkt and biochemical properties of its gene product. These studies should help delineate the molecular basis of skeletal development, and the kkt mice will provide us with an animal model for skeletal abnormalities, and help in the design and evaluation of novel therapies for any analogous human disorder.