Secreted collagens compose 15–20% of our dry body weight and are necessary for tissue formation. Dysregulated collagen secretion affects every organ system and is the pathophysiological hallmark of a broad range of diseases encompassing collagenopathies and fibrosis. Modulation of excessive collagen deposition could, therefore, offer an effective disease-modifying therapeutic approach. One solution to this problem comes from our studies of how these bulky cargoes are exported from the endoplasmic reticulum (ER), despite being too large to fit into a conventional COPII vesicle. Our discovery of TANGO1 has made the pathway of bulky cargo secretion amenable to molecular analysis and therapeutic control. TANGO1 connects collagen in the ER lumen to cytoplasmic membrane-sculpting machinery, including COPII coat components. A TANGO1 filament surrounds, corrals, and scaffolds COPII coat assembly at an ER exit site (ERES). It recruits a multisubunit tethering complex to link ER export to retrograde COPI-coated ERGIC membranes. Altogether, TANGO1 stabilizes a transient tunnel for bulky secretory cargo export without involving a bona fide vesicular intermediate as per Palade’s classical model of protein transport (Figure 1). We developed membrane-permeant peptide inhibitors of TANGO1. These peptides act as competitive inhibitors of TANGO1 function, allowing us to control collagen secretion in cells, primary tissue derived from patients with scleroderma, and in vivo, including in a murine model of skin fibrosis. Our results demonstrate that acute control of TANGO1 could provide a disease-modifying therapy for such collagenopathies.

To regulate their homeostasis, cells need to address specific proteins and lipids toward particular compartments in a tightly controlled manner. Golgi-dependent trafficking plays a crucial role in these processes. Although our understanding of the mechanisms of intra-Golgi transport and sorting has significantly improved over the past two decades, the underlying complexity of transport routes, encompassing mechanisms and dynamics, is only beginning to be revealed. Over the years, we have developed several versatile assays to monitor and quantify the transport of cargoes to the cell surface, such as the RUSH assay and the CATCHFIRE system. These assays provide powerful tools for studying and perturbing cell dynamics in real-time. Recently, we applied these tools to gain a deeper understanding of how the cell surface PD-L1 is translocated through the secretory pathway and subsequently transported to the cell surface. Additionally, we leveraged our trafficking assays to develop novel translational approaches, screen for inhibitory molecules, and establish tunable cell-based therapies.

The ability of the brain to constantly adapt its organization to ever-changing stimuli is termed ‘plasticity’ and is a prominent feature not only of learning and memory in the adult, but also of neuronal circuit assembly during developmental critical periods. Connections that are the most active become stronger and more stable, while the less active ones weaken and eventually get eliminated. How does activity make specific synapses stronger or weaker and how does it serve synaptic circuit refinement? In both immature and mature circuits, long-term changes in synapse function and organization involves signaling which regulate the traffic of synaptic proteins including cell adhesion molecules, scaffolding proteins and receptors, but also requires the expression of specific genes through transcription and translation dependent mechanisms. During this seminar, I will first present how the activity-dependent local translation of synaptopodin, a protein related to the spine apparatus, allows the input-specific molecular tagging of mature hippocampal synapses. I will then present current work in which we investigate how specific connections get molecularly encoded in the developing olivo-cerebellar system by implementing the patch-seq technique.

Insults to the central nervous system (CNS) induce permanent cognitive, sensory and/or motor disabilities, as the mature CNS is not able to regenerate. Because of the continuous increase of traumatic injuries cases (such as spinal cord injuries) or chronic neurodegenerative diseases, along with the lack of treatment, promoting neuronal growth, repair and functional recovery represent a great challenge for neurobiology, patients and public health. Since 2008, CNS regeneration has been unlocked, in part, by the modulation of neuronal molecular pathways. These master regulators promote regeneration from few millimeters to long distance regeneration when combined. However, there is still important limitations to achieve full functional recovery and patient’s treatment. Indeed, none of these molecules induce sufficient axon growth to allow complete circuit reconstruction. Moreover, most of these candidates cannot be used as therapy because of their large spectrum of action and potential oncogenic side effects. Thus, there is still a need to identify new molecules controlling CNS regeneration and define precisely their underlying molecular mechanisms in order to develop innovative treatments. Recently, our team identified protein synthesis as a key mechanism to promote axon regeneration. Particularly, we demonstrated that the translational complex (ribosomes and their interacting proteins) is a direct regulator of protein synthesis with specific modulation of the ribo-interactome and ribosomal proteins. Our work shed the light on the role translation, allowing the understanding of the molecular mechanisms at play during regeneration.

In animals, the nervous system is composed of a high diversity of neuronal cell types. During development, the correct number of neurons of each neuronal cell type has to be produced so that the nervous system can function properly. How such a level of precision is reached in a robust manner remains poorly understood. To address this question our strategy is to combine genome engineering methods and quantitative microscopy approaches to characterize the dynamics of key molecular players in vivo with single cell resolution. We use C. elegans as a biological system. More precisely, we are analyzing how the terminal divisions of neuronal progenitors are regulated by the Wnt pathway and how precise transcriptional differentiation programs are subsequently activated in a robust manner.

As the renaissance philosopher Michel De Montaigne said: ‘life is only movement’. Locomotion is a stereotyped behavior used by animals to find food, mates or to escape from predators. In animal appendages, the morphologies of muscles ensure precise movements. These muscles are innervated by a unique wiring of motoneuron axon terminals controlling the timing and intensity of muscle contraction. How do muscles and motoneurons (MNs) coordinate their development to establish unique axon-muscle connections? How do muscles acquire their unique morphologies?
My team wants to answer these questions by determining at the single cell level the genetic program controlling the development of muscle morphologies and of the axon-muscle connectome architecture in Drosophila legs. We use single cell RNA profiling and a novel 3D spatial transcriptomic approach combined with state-of-the-art techniques to visualize and selectively modify the genotype of individual cells in a developing or adult organism. We determine the impact of these manipulations on cell architecture with state-of-the-art microscopy and on locomotion with unique behavioral technologies.
During the first part of the seminar I will speak about recently published work on the Development of muscle innervation: What are the molecular and cellular mechanisms controlling the building of the axon-muscle connectome? Then, I will speak about non-published work on the Development of individual muscle morphologies: Is there a genetic program in adult MNs and muscles actively maintaining the architecture of the muscle innervation once built?

The identity of somatic and pluripotent cells can be epigenetically reprogrammed and forced to adapt a new functional cell state by different methods and distinct combinations of exogenous factors. The aspiration to utilize such in vitor reprogrammed pluripotent and somatic cells for therapeutic purposes necessitates understanding of the mechanisms of reprogramming and differentiation and elucidating the extent of equivalence of the in vitro derived cells to their in vivo counterparts. In my presentation, I will present my group’s recent advances toward understanding these fundamental questions and further detail our ongoing efforts to generate developmentally unrestricted human naive pluripotent cells with embryonic and extra-embryonic developmental potential. I will expand on new avenues for utilizing custom made electronically controlled ex utero platforms and optimized conditions for growing natural mammalian embryos ex utero for extended periods capturing both the gastrulation and organogenesis until advanced stages, for better studying of stem cell transitions during embryogenesis and organogenesis. I will detail how the latter platforms offered an exclusive technical platform to demonstrate and unleash the self-organizing capacity of mouse naïve PSCs to generate post-gastrulation organ-filled whole synthetic embryos with both embryonic and extraembryonic compartment ex utero. Collectively, I will be highlighting prospects for new platforms for advancing human disease and developmental modelling.

DIn most animal species including humans, commissural axons connect neurons on the left and right side of the nervous system. This communication between the two sides of the brain and spinal cord is necessary for a series of complex function, including binocular vision, coordinated locomotor movements, and sound direction localization. In humans, abnormal axon midline crossing during development causes a whole range of neurological disorders ranging from congenital mirror movements, horizontal gaze palsy, scoliosis or binocular vision deficits. The mechanisms which guide axons across the CNS midline were thought to be evolutionary conserved but our recent results suggesting that they differ across vertebrates. We obtained genetic evidence challenging the idea that long-range gradients of diffusible factors, such as netrin-1 attract commissural axons to the midline. I will also discuss the evolution of visual projection laterality during vertebrate evolution. In most vertebrates, camera-style eyes contain retinal ganglion cell (RGC) neurons projecting to visual centers on both sides of the brain. However, in fish, RGCs are thought to only innervate the contralateral side. This suggested that bilateral visual projections appeared in tetrapods as an adaptation to aerial vision. Using 3D imaging and tissue clearing we found that bilateral visual projections exist in non-teleost fishes. We also found that the developmental program specifying visual system laterality differs between fishes and mammals.

David Gems is a founding member of the Institute of Healthy Ageing (IHA) at University College London, where he works as Professor of Biogerontology and Research Director. Much of his work uses the nematode worm C. elegans to understand the fundamental mechanisms that cause the ageing process, including late-life disease. He also contributed to studies of aging in other nematodes, Drosophila, the mouse and Pacific salmon, and penned articles on the ethics of ageing research. He published over 160 articles, mostly on ageing.

Polycystic ovary syndrome (PCOS) is the major reproductive and metabolic disorder affecting 10-18% of women in reproductive age. Beyond its implications leading to female infertility, the disease is associated with several metabolic disruptions, cardiovascular diseases, and psychosexual disorders. Despite this heavy health burden, there is currently no cure for this syndrome.
My talk will summarize some recent discoveries showing that in animal models prenatal exposure to elevated levels of anti-Müllerian hormone (AMH) predisposes female offspring to develop reproductive and metabolic traits typical of the human disease. We capitalized on this new PCOS-like model to dissect the brain and peripheral developmental basis of PCOS inheritance. Our findings show that the transmission of PCOS reproductive and metabolic dysfunctions to multiple generations occurs via altered landscapes of DNA methylation and highlight a roadmap to new diagnostic and therapeutic avenues of the disease.
Women with PCOS also often suffer from sexual dysfunction; however, the developmental and central mechanisms mediating this behavioral derangement are unclear. In this talk, I will also present a recent investigation providing compelling evidence that sexual dysfunction in PCOS is associated with specific changes in central hypothalamic and limbic circuits regulating sexual behavior in mammals. Coupling viral-based in vivo chemogenetic manipulation with behavioral tests and pharmacological preclinical therapeutic strategies, we identified the contribution of specific neuronal populations, which are required for the display of normal sexual behavior in female mice.
Altogether, these works have broad repercussions for our understanding of developmental reprogramming in the female brain leading to disturbances in hypothalamic circuitry driving reproductive, metabolic and sexual dysfunction in PCOS and provide grounds to novel prospective therapeutic venues.

The enormous diversity of cell types in any animal model system is defined by neuron type-specific gene batteries that endow distinct cells with distinct anatomical and functional properties. Based on our own work in C. elegans as well as recent gene expression studies in vertebrates and flies, I propose that the diversity of neuronal cell types can be reduced to a simpler descriptor, the combinatorial expression of a specific class of transcription factors, encoded by homeobox genes. Functional studies in multiple animal model systems have corroborated the importance of homeobox genes in specifying neuronal identity. Recent unpublished work from my laboratory also shows that apart from controlling neuron-type specific gene batteries, a specific homeobox gene subfamily also control pan-neuronal identity features. I propose that the preponderance of homeobox genes in neuronal identity control is a reflection of an evolutionary trajectory in which an ancestral neuron type was specified by an ancestral homeobox genes and that this functional linkage then duplicated and diversified to generate distinct cell types in an evolving nervous system.

Huntington’s disease is caused by the abnormal polyglutamine expansion in the N-ter part of huntingtin (HTT), a large protein of 350kDa. Over the past years, we proposed that HTT acts a scaffold for the molecular motors and through this function, regulates the efficiency and directionality of vesicular transport along microtubules in neurons. In particular, HTT controls the microtubule-based fast axonal transport (FAT) of neurotrophic factors such as BDNF. HTT function in transport is modulated by direct phosphorylation/dephosphorylation via specific signaling pathways. Importantly, polyQ expansion in HTT alters this function, leading to a decrease in neurotrophic support and death of striatal neurons. The defect in transport might not be restricted to axons but could also involve defects in the retrograde transport of TrkB in striatal dendrites.
In addition to the role of HTT in scaffolding the molecular motors both in cortical and striatal neurons, we found that HTT scaffolds GAPDH on vesicles and that vesicular GAPDH is necessary to propel vesicles in GAPDH deficient neurons. Here we will extend these findings and discuss how HTT by specifically localizing the glycolytic machinery on vesicles may supply constant energy for the transport of vesicles over long distances in axons.

In some cases genetic "memories" are transmitted across generations without changes in DNA sequences. This type of memory is referred to as transgenerational epigenetic inheritance and can be mediated by small RNA populations and changes to chromatin. Epigenetic inheritance is probably best understood at the molecular level in the nematode C. elegans due to their short life-span and easy genetics. Here, I will describe a novel method for silencing genes in germ cells and early development using a class of small RNAs (piRNAs). We have used this silencing system to determine conditions where memories are inherited for a few generations (typically, three to six generations) and conditions where the memory becomes essentially permanent.

Satellite cells are muscle stem cells (SCs), which play essential roles in muscle repair and maintenance. One fundamental question is how such cells are specified and then protected from differentiation for a prolonged period of time. To investigate this question, we used as a model the recently identified Drosophila SCs and found that it involves a switch in RNA-isoforms coding for the transcription factor Zhf1/ZEB, a key player in SC maintenance. This switch, under Notch control, enables SC to escape differentiation by producing an alternate ZEB-short RNA isoform, which lacks the miR-8/miR-200 seed site present in ZEB-long isoforms. This mechanism may be of wide biological relevance. Another timely and poorly understood question is how SCs are activated and behave for rebuilding muscles following injury. My research program aims at elucidating cellular aspects of SC activation in a living animal and the molecular control of this behavior.
Hadi Boukhatmi and Sarah Bray (2018). A population of adult satellite-like cells in Drosophila is maintained through a switch in RNA-isoforms. eLife 2018;7:e35954.
Hadi Boukhatmi, Torcato Martins, Zoe Pillidge, Tsveta Kamenova and Sarah Bray (2020). Notch mediates inter-tissue communication to promote tumorigenesis. Current Biology 30, 1-12.

Brief pulses of dopamine in the striatum are critical for reward-mediated learning, and the temporal coincidence of dopamine and other neuromodulators bears important significance in the cellular integration of these signals. Our approach is mainly based on monitoring the dynamics of cyclic nucleotide signaling with biosensors in mouse brain slice preparations, combined with in silico simulations. Our experiments show that the presence of specific isoforms of signaling enzymes in the striatum makes these neurons highly responsive to brief dopamine transients. We are currently analyzing how these features could lead to novel therapeutic strategies for Parkinson’s disease.