Mechanisms underlying homeotic function across developmental transitions

The cellular components of the nervous system form and function under the directions of the genes. But how does the genetic program that guides the formation of the nervous system switch into the program that controls the physiology of mature neurons in adult organisms?

We have recently explored this question in the fruit fly Drosophila melanogaster, an excellent model system in modern genetics, and discovered that the Hox genes - which encode a group of key developmental genes evolutionarily conserved from insects to humans - control both the development, as well as the physiological properties of mature neurons modulating behaviour. This system, therefore, offers an excellent opportunity to determine the mechanisms by which specific genes control the biology of neurons during their differentiation and mature life in the adult organism.

This is important given that it will inform us on how cells control their internal genetic programmes to undergo 'cellular transitions': points at which the biology of cells changes quickly and dramatically, transforming a cell 'under development' into the final, mature cell that will remain in the adult organism for a long time. Because at a fundamental level, neuronal development and function follow common principles across all animals, knowledge produced from our work in the fly is expected to impact the understanding of the fundamental neurobiological processes in other species too, including humans.

The plan exploits the modern Drosophila toolkit and combines the use of genetic techniques to label a specific subset of neurons, termed dopaminergic neurons, which play key roles in movement control in insects as well as in mammals. Through this approach we will:
1) Artificially reduce the expression of the Hox genes, and use advanced cell-sorting techniques and modern RNA sequencing to determine the effects of this treatment on the genetic programme of dopaminergic neurons changes, obtaining a catalogue of all genes whose expression is under Hox gene control.
2) We will then use the gene lists produced above to generate and test mechanistic models to explain how the Hox genes might control gene networks within dopaminergic neurons, thus allowing them to develop and function normally.
3) In the last unit of work we will determine how genes under Hox-control relate to specific cellular roles in developing and mature dopaminergic neurons.

The work will thus help us understand how genes mould the biology of neurons within the normal animal, and contribute to decode the genetic basis of animal development, neurophysiology and behaviour. Our research will also contribute to the understanding of how neurons in general establish their identity within the developing and mature 'healthy' brain, providing a framework for the identification of changes linked to neuro-developmental and neurodegenerative diseases. The basic knowledge on the underpinnings of neuronal transitions is expected to also add to the field of stem cell biology and regenerative medicine, where cells are taken into specific fates via artificial manipulations to understand processes in health and disease.

The project stems from our close understanding of the Hox gene system, strong track record in the analysis of gene function in flies, a wealth of preliminary data, and our proved ability to investigate developmental and physiological processes in neurons.

The work will be developed within the highly collaborative and interdisciplinary community of Sussex Neuroscience, an internationally-leading centre for neuroscience research with more than 50 neuroscience research labs based on the Sussex campus, and will further benefit from the input of expert collaborators in Sussex, Oxford and Germany who will be sharing their technical expertise during the development of specific aspects of the project. Altogether, this puts us in an ideal position to develop this project successfully within the period of the grant.

During development, gene regulatory processes integrate intrinsic and extrinsic information to mould cellular biochemistry allowing cells to acquire their specific morphological and functional specialisations. Once development concludes, cellular systems must deactivate the old genetic programme that guided their differentiation and activate the new programme that controls the biochemistry underlying physiological and maintenance roles in the mature state. Despite the centrality of this transition, the ways in which gene regulatory systems modify the biology of cells at this critical period are not well understood.

Here we investigate this problem in Drosophila, studying the gene regulatory mechanisms that control the transition between neuronal differentiation and the onset of neural physiology: we will map the mechanisms by which the Hox genes control the biochemistry and biological properties of a subpopulation of dopaminergic neurons as they move from differentiation into performing essential physiological functions in the adult.

The plan combines modern neural transcriptomics with biochemical approaches (CUT&RUN, TaDa, CATaDa) and neural-specific developmental and physiological analysis to map the molecular basis underlying the transition from neural differentiation into the mature neuronal state, testing the hypothesis that the Hox system provides a bi-modal regulatory mechanism that controls neuronal differentiation and the physiological properties of mature post-mitotic neurons via distinct molecular pathways.

The Hox genes encode a family of evolutionarily conserved transcription factors with key roles in the specification of neural developmental along the body axis. Recent work from my lab has revealed that Hox gene expression is also essential for mature neuronal function and behaviour, offering an opportunity to determine how the same gene regulators can re-wire neurons adjusting their biology as they navigate through developmental transitions