Biology subjects

Konstantinides, N.

Publications and source records attributed to Konstantinides, N..

8 recordsLinked to original sources

bioRxiv2026

Evolution and integration of a novel cell type in the housefly Love Spot

The addition of new neuron types is thought to underlie the evolution of complex nervous systems, yet the mechanisms by which they arise remain unclear. Here we investigate the evolution of a novel target detection photoreceptor in the housefly Musca domestica. In males, a dorso-frontal eye region known as the "Love Spot" enables rapid detection and tracking of females during mating flights. In this region, R7 photoreceptors - normally dedicated to color vision - are repurposed for target detection through altered Rhodopsin expression, physiology, and circuit connectivity. We show that these Love Spot R7 cells (LsR7) are initially specified as canonical R7 photoreceptors but later adopt a chimeric identity combining transcription factors normally associated with either color or motion vision. The sex-determination transcription factor Doublesex (Dsx) is strongly upregulated after R7 specification and, together with the transcription factor Spineless, drives the LsR7 gene regulatory program. Because Dsx upregulation occurs after initial axon targeting to the medulla, LsR7 axons subsequently shorten to connect with lamina neurons and OFF-pathway motion vision circuits. These findings show how new combinations of cell-identity regulators can generate novel neural cell types while revealing developmental constraints imposed by evolutionary history.

Developmental Biology↗

bioRxiv2026

Evolutionary dynamics of temporal transcription factor series in the insect optic lobe

The nervous system consists of a wide variety of neuronal cell types arranged into complex circuits that support a broad range of behaviors. Patterning of neural stem cells in time through the sequential expression of series of temporal transcription factors is a key contributor to the generation of neuronal diversity. How do temporal series arise and diversify across species to support the evolution of neuronal type? Here, we reconstruct the evolutionary history of the temporal series in the visual brain of insects, spanning 400 million years of evolution; we identify a conserved temporal ground plan, as well as species-specific variations. We find that temporal programs evolve through recurrent modifications of a shared scaffold. Finally, we show that such evolutionary changes in temporal patterning can result in different neuronal type identities. Together, our results reveal both the deep conservation and evolutionary plasticity of temporal patterning programs, and establish temporal transcription factor series as a tractable substrate for the evolution of neuronal diversity.

developmental biology↗

bioRxiv2025

Lifelong maintenance of locomotion by embryonically active dopamine neurons

Locomotor skills arise early in life and are maintained throughout an animals lifespan, yet how this continuity is achieved despite major neural remodeling remains unclear. Using Drosophila, which undergoes complete metamorphosis, we show that the activity of embryonically established dopamine neurons (DANs) is essential for locomotion across all developmental stages and adulthood. Through stage-specific behavioral assays, optogenetics, in vivo brain imaging, and fluorescent neuronal tracking, we identify a subset of ventral nervous system (VNS) DANs that modulate locomotor function throughout life. Transcriptomic analyses reveal that they maintain expression of developmental transcription factors. Knocking down these factors, particularly Antp and Pdm2, in post-mitotic VNS DANs reduces neurite arborization and impairs adult locomotion. These findings uncover a previously overlooked function for embryonic DANs and suggest that stable locomotion during nervous system maturation relies on persistent developmental regulator expression coupled with structural remodeling.

neuroscience↗

bioRxiv2025

Regeneration of distinct complex structures in the annelid Platynereis is partially based on common morphological, cellular, and molecular events

Many metazoan species harbor fascinating regenerative capabilities, but the underlying mechanisms remain poorly understood. Whether the capacity to regenerate complex structures successfully relies on common or divergent features is still an open question. To identify the key molecular and cellular elements necessary for successful regeneration, we investigated the efficient regeneration of two distinct complex structures in the annelid worm Platynereis dumerilli. By combining classical morphological and developmental approaches, with state-of-the-art single-cell RNA sequencing and analysis, we conducted a comprehensive comparison of locomotory appendage and posterior part regeneration. We uncovered the rich cell type diversity of this Platynereis appendage, over a third of which are nerve-related populations, highlighting the importance of its sensory function. We also described its regenerative process at the morphological and cellular levels, defining stages that include the formation of a proliferative blastema. We then compared posterior part and appendage blastemas, specifically assessing their cell diversity and cell differentiation trajectories. We found transcriptionally similar epithelial and mesodermal progenitors at play during posterior and appendage regeneration, although their specific trajectories differed to some extent. Our work, revealing partial morphological, molecular and cellular parallels between these two efficient regenerations within a single species, sets the foundation for addressing the fundamental question of regeneration success in animals.

developmental biology↗

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↗

bioRxiv2021

Fate transitions in Drosophila neural lineages: a single cell road map to mature neurons.

Neuron specification and maturation are essential for proper central nervous system development. However, the precise mechanisms that govern neuronal maturation remain poorly understood. Here, we use single-cell RNA sequencing, combined with a conditional genetic strategy to analyse neuronal lineages and their new born neurons in the Drosophila larval brain. A focused analysis on the transcriptional alterations that occur right after neuron generation revealed that neuron maturation starts shortly after neuronal birth, with transcription, but no translation, of mature neuronal features such as neurotransmitter (NT) genes. Using NT gene Choline acetyltransferase as an example, we show that the timings of translation initiation are not solely dependent on neuron age but are rather coordinated with the animal developmental stage. This study is the first characterization of the initial phases of neuron maturation, supporting a model where neuron maturation is coordinated with the animal developmental stage through post-transcriptional regulation of terminal effector genes.

neuroscience↗

bioRxiv2021

A comprehensive series of temporal transcription factors in the fly visual system

The brain consists of thousands of different neuronal types that are generated through multiple divisions of neuronal stem cells. These stem cells have the capacity to generate different neuronal types at different stages of their development. In Drosophila, this temporal patterning is driven by the successive expression of temporal transcription factors (tTFs). While a number of tTFs are known in different animals and across various parts of the nervous system, these have been mostly identified by informed guesses and antibody availability. We used single-cell mRNA sequencing to identify the complete series of tTFs that specify most Drosophila medulla neurons in the optic lobe. We tested the genetic interactions among these tTFs. While we verify the general principle that tTFs regulate the progression of the series by activating the next tTFs in the series and repressing the previous ones, we also identify more complex regulations. Two of the tTFs, Eyeless and Dichaete, act as hubs integrating the input of several upstream tTFs before allowing the series to progress and in turn regulating the expression of several downstream tTFs. Moreover, we show that tTFs not only specify neuronal identity by controlling the expression of cell type-specific genes. Finally, we describe the very first steps of neuronal differentiation and find that terminal differentiation genes, such as neurotransmitter-related genes, are present as transcripts, but not as proteins, in immature larval neurons days before they are being used in functioning neurons; we show that these mechanisms are conserved in humans. Our results offer a comprehensive description of a temporal series of tTFs in a neuronal system, offering mechanistic insights into the regulation of the progression of the series and the regulation of neuronal diversity. This represents a proof-of-principle for the use of single-cell mRNA sequencing for the comparison of temporal patterning across phyla that can lead to an understanding of how the human brain develops and how it has evolved.

developmental biology↗

bioRxiv2018

Phenotypic convergence in the brain: distinct transcription factors regulate common terminal neuronal characters

Transcription factors regulate the molecular, morphological, and physiological characters of neurons and generate their impressive cell type diversity. To gain insight into general principles that govern how transcription factors regulate cell type diversity, we used large-scale single-cell mRNA sequencing to characterize the extensive cellular diversity in the Drosophila optic lobes. We sequenced 55,000 single optic lobe neurons and glia and assigned them to 52 clusters of transcriptionally distinct single cells. We validated the clustering and annotated many of the clusters using RNA sequencing of characterized FACS-sorted single cell types, as well as marker genes specific to given clusters. To identify transcription factors responsible for inducing specific terminal differentiation features, we used machine-learning to generate a random forest model. The predictive power of the model was confirmed by showing that two transcription factors expressed specifically in cholinergic (apterous) and glutamatergic (traffic-jam) neurons are necessary for the expression of ChAT and VGlut in many, but not all, cholinergic or glutamatergic neurons, respectively. We used a transcriptome-wide approach to show that the same terminal characters, including but not restricted to neurotransmitter identity, can be regulated by different transcription factors in different cell types, arguing for extensive phenotypic convergence. Our data provide a deep understanding of the developmental and functional specification of a complex brain structure.

developmental biology↗