LHX6, MTG8 and MTG16: functions and interactions in cortical interneuron development

Inhibitory interneurons play pivotal roles within the cortex, the seat of higher order information processing in mammals. Defects in cortical interneurons cause neural network imbalance and can lead to seizure-based and neurodevelopmental cognitive and psychiatric impairments such as autism and schizophrenia. Genetic mutations affecting interneuron maturation and leading to cognitive dysfunction have been identified but we are far from understanding the genetic complexity of cortical interneuron development and how genetic defects can lead to disorders.

There is a large diversity of interneurons in the cortex and it is largely unknown how this diversity is established in the developing embryo. We discovered two novel genes, Mtg8 and Mtg16, that function in concert with the master regulator of cortical interneuron development Lhx6 in the determination of interneuron subtypes in animal models. We aim to understand the relationship between the three genes and their specific requirements for interneuron development in the embryo. We will also examine wider genetic programs that are triggered by the action of these proteins in order to gain further insight into the genetic makeup that dictates interneuron cell identity. Ultimately, this knowledge will be invaluable not only in understanding interneuron-based developmental disorders, but also in the generation of interneurons from stem cells for use in transplantation repair therapies -a route already adopted experimentally for epileptic conditions in animal models.

Inhibitory interneurons form essential elements of cortical circuits. There are several distinct subtypes of interneurons in the mature cortex; they play different roles in network function and have distinct origins in the embryonic telencephalic neuroepithelium. The molecular mechanisms of interneuron subtype specification are largely unknown. We identified two novel transcriptional regulators, MTG8 and MTG16, that are enriched in interneurons expressing the master regulator of cortical interneuron development LHX6. Our pilot data demonstrate a requirement for MTG factors in LHX6-dependent cortical interneuron specification pathways. We hypothesize that the MTG proteins act in the same genetic pathway(s) as LHX6, and we propose a series of experiments to determine the nature of their interaction as well as their specific and common functions in interneuron lineages. We will use a combination of genetic approaches in vivo and biochemical approaches in vitro. The work will significantly advance our understanding of the genetics of interneuron development and will have far reaching impact on neurodevelopmental disease research and stem cell therapies.

The proposed work will elucidate the role of the transcriptional regulators MTG8 and MTG16 in cortical interneuron development and their interplay with the master regulator of cortical interneuron development LHX6. Given the importance of inhibitory interneurons in cortical processing and neurodevelopmental or other seizure-based disorders, the research will benefit several branches of academic and translational research.

1. There will be immediate benefits to the interneuron development academic research field as the work will provide further insight into the specification and differentiation of cortical interneurons and the molecular drivers behind these processes.

2. There will be immediate benefits to the stem cell research community where embryonic and induced pluripotent stem cells are being used for the derivation of cortical interneurons in culture as the work will elucidate the role of the LHX6 and MTG transcriptional regulators in cortical interneuron development and potential pathways for driving stem cells into specific fates.

3. In the longer term, knowledge into the molecular specification of cortical interneurons and the role of the LHX6 and MTG proteins will allow the development of cortical interneuron subtypes in culture and the use of these in effective transplantation therapies for conditions such as epilepsy where cortical inhibition is impaired. This approach has already been applied experimentally and shown to be effective even with mixed populations of interneuron subtypes. Knowledge into the transcriptional regulation of cortical interneuron development will allow a refinement of this approach for more effective transplantation therapies. Therefore the research has the potential to contribute to the nation's health.

4. Interneurons have been implicated in neurodevelopmental diseases such as autism, schizophrenia and intellectual disability. Emerging opinions suggest commonalities in the genetic basis of these disorders. Mutations in MTG8 have been found in humans with intellectual disability suggesting a role in this disorder. Our finding of defective interneuron development in mice lacking MTG8 may provide a clue into the cognitive phenotype in humans. In the longer term, the work proposed will benefit the neurodevelopmental disease field and thus contribute to the nation's health through understanding of some of the genetic basis of interneuron-based diseases and potentially the development of effective therapies.

5. Staff working on the project will benefit by expanding and enriching their research skills through bench work and enhancing their professional skills through oral and written presentations, scientific networking and collaboration as well as public engagement when the opportunity arises. These are transferable skills highly sought after by non-academic employers. Through publications and collaborations the work will enhance the national and international profile of our Universities.

6. Public beneficiaries can vary. Immediate beneficiaries include secondary schoolchildren who may join the lab for work experience. This will provide them with a glimpse of academic research in basic science. The wider public will benefit in the long term through the availability of more effective therapies developed using knowledge gained in this project.