Biology subjects

Courgeon, M.

Publications and source records attributed to Courgeon, M..

4 recordsLinked to original sources

bioRxiv2026

Encoding neuronal shape in the stochastic dynamics of branching processes

Cell shape critically influences function, yet how complex and reproducible morphologies emerge from stochastic cellular dynamics remains unclear. Here, we investigate dendritic morphogenesis of two classes of Drosophila mechanosensory neurons with contrasting architectures, combining in vivo live imaging, quantitative analysis, cytoskeletal perturbations, and computational modeling. We show that despite sharing similar local stochastic branching rules, the two classes exhibit divergent growth dynamics that cannot be explained by standard, diffusive growth models. This discrepancy arises because Class I neurons display subdiffusive branch dynamics over long timescales, unlike Class IV. Based on these findings, we develop a minimal model with only four parameters that separates short-and long-term branch behaviors, and successfully recapitulates growth dynamics and final morphologies in both classes. Cytoskeletal perturbations reveal a functional separation between actin, which drives short-term exploratory branch fluctuations and arbor expansion, and microtubules, which tune long-term branch diffusivity and determine class-specific morphology. Together, these results establish a parsimonious, generalizable framework linking local cytoskeletal regulation to global neuronal architecture and reveal how stochastic dynamics encode reproducible cell shapes.

biophysics↗

bioRxiv2025

Gene expression cartography of a developing neuronal structure

The brain is a complex structure comprising thousands to billions of neurons that belong to thousands to millions of different neuronal types. These neurons often come from different progenitor domains and have very diverse developmental histories, yet they need to find their precise location in the brain and integrate into appropriate circuits. Therefore, describing the neuronal parts list of the brain in the form of single-cell mRNA sequencing atlases, while invaluable, lacks the spatial information that is instrumental to brain structures. While a large number of brain single-cell mRNA sequencing atlases have become available over the last years, spatial transcriptomic studies have lagged behind for a variety of reasons. Here, we use a gene expression cartography algorithm, called Novosparc, to reconstruct the spatial distribution of gene expression and cell type localization in a complex, yet tractable, developing brain structure, the Drosophila optic lobe. We generate a three-dimensional atlas of this structure, which we made available through a dedicated website (https://larva3dnovosparc.ijm.fr). This allowed us to identify spatially compartmentalized cell types and spatially patterned genes, to predict hotspots of neuronal cell death and identify the expression of neuronal type-defining transcription factors. Importantly, we identify caveats in such algorithms that could allow for the development of refined versions. Altogether, this work provides an invaluable tool for brain researchers to formulate hypotheses and paves the way for the generation of three-dimensional atlases of more complex brain structures, which will enhance our understanding of how neurons with diverse developmental lineages can integrate to form a functional brain.

developmental biology↗

bioRxiv2019

Coordination between stochastic and deterministic specification in the Drosophila visual system

Many sensory systems use stochastic fate specification to increase their repertoire of neuronal types. How these stochastic decisions are coordinated with the development of their target post-synaptic neurons in processing centers is not understood. In the Drosophila visual system, two subtypes of the UV-sensitive R7 color photoreceptors called yR7 and pR7 are stochastically specified in the retina. In contrast, the target neurons of photoreceptors in the optic lobes are specified through a highly deterministic program. Here, we identify subtypes of the main postsynaptic target of R7, the Dm8 neurons, that are each specific to the different subtypes of R7s. We show that during development the different Dm8 subtypes are produced in excess by distinct neuronal progenitors, independently from R7 subtype specification. Following matching with their respective R7 target, supernumerary Dm8s are eliminated by apoptosis. We show that the two interacting cell adhesion molecules Dpr11, expressed in yR7s, and its partner DIP{gamma}, expressed in yDm8s, are essential for the matching of the synaptic pair. Loss of either molecule leads to the death of yDm8s or their mis-pairing with the wrong pR7 subtype. We also show that competitive interactions between Dm8 subtypes regulate both cell survival and targeting. These mechanisms allow the qualitative and quantitative matching of R7 subtypes with their target in the brain and thus permit the stochastic choice made in R7 to propagate to the deterministically specified downstream circuit to support color vision.

neuroscience↗

bioRxiv2018

Control of synaptic specificity by limiting promiscuous synapse formation

The ability of neurons to distinguish appropriate from inappropriate synaptic partners in their local environment is fundamental to the proper assembly and function of neural circuits. How synaptic partner selection is regulated is a longstanding question in Neurobiology. A prevailing hypothesis is that appropriate partners express complementary molecules that match them together and promote synaptogenesis. Dpr and DIP IgSF proteins bind heterophilically and are expressed in a complementary manner between synaptic partners in the Drosophila visual system. Here, we show that in the lamina, DIP mis-expression is sufficient to promote synapse formation with Dpr-expressing neurons, and that DIP proteins are not necessary for synaptogenesis but rather function to prevent ectopic synapse formation. These findings indicate that Dpr-DIP interactions regulate synaptic specificity by biasing synapse formation towards specific cell-types. We propose that synaptogenesis occurs independent of synaptic partner choice, and that precise synaptic connectivity is established by limiting promiscuous synapse formation.

neuroscience↗