Projects in the Hidalgo lab   

 

The mammalian neurotrophin protein family - formed of NGF, BDNF, NT3 and NT4 - underlies most aspects of nervous system development and function in the mammalian and human brain. They link structure and function in the brain, conferring it with the plasticity that enables it to make adjustments during growth and during learning. Neurotrophins regulate neuronal survival, cell proliferation, neuronal differentiation, axonal patterns, dendritic aroborisation, connectivity, synaptogenesis, synaptic transmission, learning and memory. Many neurodegenerative and psychiatric diseases result form alterations in neurotrophin function.

We have shown that a neurotrophin family in Drosophila formed by DNT1, DNT2 and Spz functions in nervous system development to adjust neuronal number during connectivity in the fly (Zhu et al 2008). This means that a common mechanism is shared across the animals to form the nervous system and brain in a plastic manner. 

DNT1 was identified by sequence homology to BDNF. We then showed that although sequence divergence is high, the functional cystine-knot domain is conserved, and the spacing of the characteristic 6 Cysteines isconserved in neurotrophin homologues present throughout the invertebrates (sea urchin, acorn worm, lancet) as well as vertebrates and mammals. MOst importantly, we showed that there is functional conservation. Loss of DNT1 function leads to neuronal apoptosis in the Drosophila embryonic CNS, and over-expression of mature DNT1 rescues naturally occurring cell death. Loss and gain of DNT1 function also alter targeting by motoraxons to the muscles (Zhu et al 2008).

DNT1 is a paralogue of spz. Spz has been shown by others to be structurally related to the mammalian neurotrophin family, as Spz crystals can be aligned with those of NGF (Arnot et al 2010). Drosophila Neurotrophin 2 (DNT2) is closest in sequence to DNT1, and there are altogether six spz paralogue genes (Parker et al 2001). We have found that DNT1, DNT2 and Spz are all involved in embryonic CNS development, where they have partially redundant functions (mostly DNT1 and DNT2), and complementary functions (Spz vs. DNT1) (Zhu et al 2008). The expression of spz complements those of DNT1 and DNT2 in the embryonic muscles, and loss or gain of DNT1 and DNT2 function affect targeting by a set of ventral motoneurons distinct from those affected by alterations in Spz function.

We have shown that DNT1, DNT2 and Spz are required for synaptogenesis. In the mutants, there is a deficit in active zone formation, therefore a reduction in the number of synapses (Sutcliffe et al 2013). This causes a homeostatic compensation of NMJ size, to increase overall synapse number. Thus, the axonal terminals increase at the NMJ in the mutants, leading to a higher number of synaptic boutons. Although these have fewer synapses, the overall increase in bouton number results in an overall normal number of active zones, and a consequent normal synaptic transmission and normal larval crawling behaviour.

We wish to work out how and whether all Spz paralogues influence CNS structure and function, from embryo to the adult brain, thus we are currently investigating what each of spz paralogues does in the contexts of brain structure and growth, plasticity and behaviour.

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Drosophila neurotrophins and the Spz protein family:

circuitry, signalling and function.

We are now addressing questions such as: What are the neural circuits involving the DNTs? Did elaborations in DNT signalling in the course of evolution result in distinct brain types and behaviours or not? What are the similarities and differences between the DNTs and the mammalian neurotrophins? What are the signalling pathways? Are brain structure and function linked in flies too, and does this involve the DNTs?

We are collaborating with structural biologists and biochemists in the team of Prof. Nick Gay  (Department of Biochemistry, University of Cambridge) to solve the mechanistic questions.

We look at all stages, from embryo to adult, and our approaches include classical genetics, molecular biology, cell culture, imaging and behaviour.

See Zhu et al (2008) PLoS Biology 6, e284 ; Sutcliffe et al 2013 PLoS One 8(10): e75902

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