Akira Imamoto, D.D.S., Ph.D.

Research Summary

Mammalian Genetics and Developmental Biology

We currently focus on elucidating the molecular and developmental mechanisms underlying a human syndrome called DiGeorge/velocardiofacial syndrome (DGS/VCFS) (OMIM: 188400 and 192430):

DGS/VCFS is the most frequent deletion syndrome, affecting approximately 1 in 4,000 live births. The common manifestations of this syndrome include cardiovascular defects, aplasia or hypoplasia of the thymus and parathyroid glands, and craniofacial anomalies. Urogenital defects, learning disabilities, and other psychiatric disorders are also common.

The molecular basis of DGS comprises heterozygous deletions at 22q11.21 likely mediated by recombination between chromosome 22-specific low copy repeats (LCR22s) scattered around this region. The most common deletion encompasses 3 Mb in approximately 90% of the patients. Two candidate genes, TBX1 and CRKL, have been mapped within this region.

Although CRKL is broadly expressed, it is concentrated in neural crest cells and their derivatives during development. We have found that knockout (inactivation) of this gene produces a phenotype that closely mimics the symptoms of DGS/VCFS. These results therefore suggest that defective CRKL-dependent pathways underlie the molecular etiology of DGS/VCFS. We currently investigate the relationship of CRKL with TBX1 and other 22q11 genes during the process that determines correct anterior-posterior identities of thepharyngeal apparatus. In addition, our results suggest that CRKL is required for cell survival, patterning, and fate determination. We are testing this hypothesis in order to understand the biology of pharyngeal arch development which is coordinated by interaction between theendoderm, ectoderm, mesoderm, and neural crest-derived mesenchyme.

Cell Biology

We are also interested in other fundamental questions in cell biology concerning inter- and intracellular signaling that influences decision making processes of cell behavior and fate that are essential for normal development.  

CRKL encodes an adapter protein of the CRK family, consisting of multiple protein-protein interaction domains known as SH2 and SH3 domains. We have learned that CRKL protein shuttles between different subcellular compartments/organelles in the cell in response to external stimuli such as growth factors and adherence to the extracellular matrix. One of the important sites to which CRKL moves is a structure called the focal adhesion. Focal adhesion structures contain large clusters of proteins that participate in cell-matrix adhesion as well as physical and functional links to the cytoskeleton. Such changes in location are induced presumably by tyrosine phosphorylation on CRKL SH2 binding proteins. The functional consequence of translocation is then mediated by the ability of CRKL to bring another protein to the site through its SH3 domains, thus promoting specific interactions of multiple proteins which may otherwise occur only in a non-specific (random) manner. When CRKL is made constitutively localized to focal adhesions, cells become readily motile with increased activity of small G-proteins such as Rac and Cdc42. In fibroblasts deficient for CRKL, directional migration toward the extracellular matrix is impaired. 

It has long been known that many types of cells require cell adhesion to the extracellular matrix not only for physical support but also for their survival, proliferation and other physiological functions. Thus, CRKL may play an important role in bridging adhesion signals to the cellular machinery that coordinates signals induced by other extracellular stimuli such as growth factors in order to elicit appropriate cellular responses.

We are investigating the role of CRKL in cell migration, survival, proliferation, and differentiation in tissue culture, in order to understand the essential role that CRKL plays in organogenesis and tissue morphogenesis during development as well as its role as an oncogene in models of cancer.