4 YEAR PhD IN NEUROSCIENCE
Department of Cell and Developmental Biology
Neuronal organisation within the vertebrate central nervous systems largely follows two main schemes. In one scheme, functionally related neurons are found stratified in layers or laminae, for example in the cerebral cortex and dorsal horn of the spinal cord. The second, perhaps prevalent, scheme organises functionally related neurons into clusters or nuclei, for instance the thalamic relay nuclei and the organisation of motor neurons in the ventral horn of the spinal cord. Whilst lamina formation has been the focus of much current research and so is relatively well understood, the processes and molecular mechanisms that generate neuronal nuclei remain enigmatic. Our research is aimed at understanding how nuclear formation occurs and what the functional consequences are of this organisational principle. We are using the nuclear organisation of spinal motor neurons as a model system to study this process.
We have shown that the combinatorial expression of members of the cadherin family of cell adhesion molecules plays a role critical to the specificity with which motor neurons cluster to form pools. Different motor pools can be distinguished by their combinatorial expression of these cadherins. Perturbation of this cadherin expression using a dominant negative construct perturbs general motor neuron organisation. Further, perturbation of combinatorial cadherin expression to equalise it between two motor pools selectively desegregates these pools. Together, these data implicate strongly combinatorial cadherin expression in the selectivity with which motor neurons organise into pools. However, several key questions remain, are the focus of the research in the group and make ideal PhD projects.
1) How does combinatorial cadherin expression operate to direct specificity of cell-cell interaction?
To address this, we can assess the specificity of interaction of cadherins in the context of the presentation of multiple cadherins in a single cell. We are using cell-line based aggregation assays, fluorescence based protein interaction assays in addition to biophysical experiments in collaboration with the group of Lawrence Shapiro at Columbia University in New York, USA.
2) Does cadherin expression direct further aspects of motor neuron development, such as peripheral axon guidance?
We are assessing the consequences to motor axon guidance of perturbed cadherin gene expression by both gain of function analyses in chick as well as loss of function analyses in mice. This work forms part of a collaboration with Masatoshi Takeichi at the RIKEN Centre for Developmental Biology in Kobe, Japan.
3) Is there a general role for cadherin gene expression in motor neuron organisation?
Misexpression of a pan-cadherin dominant negative version generates a desegregation of motor neuron organisation. Additionally, perturbation of function of a member of the armadillo family of catenins crucial to the adhesive potential of cadherins generates a dramatic desegregation of motor neuron organisation. Together, these data are consistent with a general role for cadherin expression in motor pool formation and allow an investigation of the general consequences to motor neuron function of pool segregation.
4) Is cadherin expression utilised in other parts of the CNS to drive specificity of neuronal interaction?
We are beginning investigate whether cadherin mediated cell interactions may contribute to the formation of motor nuclei in the hindbrain.
The techniques employed in these projects include: Mammalian cell culture and cell biology, perturbation of gene function in vivo, fluorescence and confocal microscopy both in tissue section and in time-lapse cultures and general molecular biology techniques.
Livet J., Sigrist M., Stroebel S., De Paola V., Price S.R., Henderson C.E., Jessell T.M. and Arber S. (2002)
ETS Gene PEA3 Controls the Central Position and Terminal Arborization of Specific Motor Neuron Pools.
Neuron 2002; 35, 877-892
Price, S. R., DeMarco-Garcia N. V., Ranscht, B. and Jessell, T. M. (2002)
Regulation of Motor Neuron Pool Sorting By Differential Expression of Type II Cadherins.
Cell 2002; 109, 205-216