Characterisation of cortical subplate neurons

Building the brain is like erecting a huge complex tower or bridge. The construction requires a dynamic scaffold which is built and modified along with the final permanent structure. After the completion of the construction the scaffold has to be dismantled at the right places and at the right time. The subplate, the earliest generated and largely transient cortical neurons is the foundation of the brain, and disruption of these cells may be the source of many developmental flaws, and therefore a fundamental topic to study. Cerebral cortical developmental disorders (schizophrenia, autism, attention deficit/hyperactivity disorder, ADHD) and perinatal hypoxic injuries (periventricular leucomalacia, PVL) involve cells of the subplate. The Molnar group has been investigating the integration of subplate cells into the intracortical and extracortical circuitry, their neurochemical properties and physiological characteristics over the last 15 years. The major hindrance of progress in the understanding of the role of this enigmatic cell population in cortical development and disease is the lack of reliable markers for these cells. In view of the selective vulnerability of this cell population and their important role in cortical development we propose to identify specific gene expression patterns in subplate and exploit this knowledge for further molecular and genetic approaches to study their role and vulnerability. These approaches require much specialised skills, which are beyond the scope of a single research group. The proposed collaboration will foster the interactions between a molecular and genetic laboratory and a cellular and anatomical group within the same Department of the same University and will open opportinities for collaboration with practising clinicians to initiate clinical applications in neuro-imaging, psychiatry, ophthalmology and neuropathology.

This proposal addresses the development of cortical circuits which is important for the understanding of many disorders such as childhood epilepsy, schizophrenia, autism and cerebral palsy. Subplate neurons are amongst the earliest generated neurons of our brain and lay the foundation of our developing cerebral cortex. They integrate into the developing intra and extracortical circuitry, providing vital support for critical developmental steps. After subserving these functions, the majority of subplate neurons die and give way to the permanent cortical circuits. The lack of the molecular characterisation and selective markers hinders the progress in this field. We will combine neuroanatomical (Molnar) with molecular genetic (Davies) techniques to identify markers for this cell population. We have generated pilot data which suggests that our approach will work, enabling us to make a significant contribution to this field. We propose the further comparisons in gene expression between layer VI and subplate cells at various developmental time points in different cortical regions (putative primary somatosensory cortex and visual cortex) using microarray analysis. Our E18 and P8 screens have already identified candidate genes which are selectively expressed or expressed at a higher level in subplate cells than in the neighbouring layer VI cells. In this proposal we (1) wish to extend the gene expression analysis to additional stages (E15 and adult); (2) study selected mouse mutants (including CTGF and Nkx2.2 KOs); (3) relate gene expression patterns to cortical circuitry; (4) generate two transgenic mice lines (one with reporter gene expression and one conditional KO); (5) investigate comparative aspects of subplate in rodent and human and (6) start to use the markers in the study of rodent models of pathological conditions (including reeler mouse, cdk5 KO and Scrambler mouse). It is our intention to start to use the new subplate markers in clinical diagnosis and we have set up collaborations with the groups of Harrison, Rutherford and Ragge to exploit these new molecular tags in the clinicopathological analysis of brain developmental disorders.