Embryonic tissues are shaped by the dynamic behaviours of their constituent cells. To understand such cell behaviours and how they evolved, new approaches are needed to map out morphogenesis across different organisms. Here, we apply a quantitative approach to learn how the notochord forms during the development of amphioxus, a basally-branching chordate. Using a single-cell morphometrics pipeline, we quantify the geometries of thousands of amphioxus notochord cells, and project them into a common mathematical space, termed morphospace. In morphospace, notochord cells disperse into branching trajectories of cell shape change, revealing a dynamic interplay between cell shape change and growth that collectively contribute to tissue elongation. By spatially mapping these trajectories, we identify conspicuous regional variation, both in developmental timing and trajectory topology. Finally, we show experimentally that, unlike ascidians but like vertebrates, posterior cell division is required in amphioxus to generate full notochord length, thereby suggesting this might be an ancestral chordate trait secondarily lost in ascidians. Altogether, our novel approach reveals that an unexpectedly complex scheme of notochord morphogenesis might have been present in the first chordates.

The casenotes of 144 doctors who had received treatment for substance misuse were analysed. There were no differences between general practitioners (n = 61) and hospital doctors (n = 58) in terms of their substance misuse histories or the problems they incurred. Differences emerged between the consultant (n = 24) and the non-consultant (n = 34) grades of hospital doctor. The consultants were older at onset of problematic use (42.6 +/- 8.6 vs. 29.9 +/- 9.8 years); they suffered fewer career problems and misused fewer substances. The most frequent pathways into substance use were personality difficulties (76 subjects, 52.8%) and anxiety or depression (46 subjects, 31.9%). A history of depression (n = 36) was associated with perceived stress at work (p = 0.014), and at home (p = 0.06). Past neurotic disturbances (n = 20) were associated with personality difficulties (p = 0.035), anxiety or depression (p = 0.004), and with an earlier onset of problematic substance use (30.2 +/- 8.3 vs. 36.5 +/- 9.8 years, p = 0.014). Principal components of possible antecedents yielded one major component on which all elements loaded; this was labelled the 'disturbance score'. This score showed a reduction with increasing age of onset of problematic substance use.

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The central nervous system of the cephalochordate amphioxus consists of a dorsal neural tube with an anterior brain. Two decades of gene expression analyses in developing amphioxus embryos have shown that despite the lack of overt segmentation the amphioxus neural tube is highly regionalized at the molecular level. However, little is known about the mechanisms that generate such precise regionalization. Proliferation is a key driver of pattern formation and cell type diversification, but in amphioxus it has never been studied in detail nor in the specific context of neurogenesis. Here, we describe the dynamics of cell division during the formation of the central nervous system in amphioxus embryos and its contributions to the regionalization of the neural axis. We show that after gastrulation, proliferation pauses to become spatially restricted to the anterior and posterior ends of the neural tube at neurula stages. Only at the onset of larval life, proliferation resumes in the central part of the nervous system. By marking specific populations and inhibiting cell division during neurulation, we demonstrate that proliferation in the anterior cerebral vesicle is required to establish the full cell type repertoire of the frontal eye complex and the putative hypothalamic region of the amphioxus brain, while posterior proliferating progenitors, which were found here to derive from the dorsal lip of the blastopore, contribute to elongate the caudal floor plate. Between these proliferative domains, we find trunk nervous system differentiation is independent from cell division, which decreases during neurulation and resumes at the early larval stage. Taken together, our results highlight multiple roles for proliferation in shaping the amphioxus nervous system.

Background: Schistosomiasis is a major Neglected Tropical Disease, caused by the infection with blood flukes in the genus Schistosoma. To complete the life cycle, the parasite undergoes asexual and sexual reproduction within an intermediate snail host and a definitive mammalian host, respectively. The intra-molluscan phase provides a critical amplification step that ensures a successful transmission. However, the cellular and molecular mechanisms underlying the development of the intra-molluscan stages remain poorly understood. Methods: S. mansoni mother sporocysts were dissociated into single cell suspensions, and live cells enriched and sequenced using the single cell 10X Genomics Chromium platform. We defined somatic and stem/germinal cell clusters, identified cell type-enriched Gene Ontology (GO) terms, and predicted transcription factor binding sites for key marker genes. Results: Six cell clusters comprising stem/germinal, two tegument, muscle, neuron, and parenchyma were identified and validated by Fluorescence in situ Hybridisation (FISH). GO term analysis predicted key biological processes for each of the clusters. Using the Self-Assembling Manifold (SAM) algorithm, three sub-clusters were identified within the stem/germinal cell population. Furthermore, transcription factor binding sites and putative transcription factors were predicted for stem/germinal and tegument clusters. Conclusions: We report a spatially validated single cell transcriptomic analysis of the first intra-molluscan stage of S. mansoni. Key cell regulators were identified, paving the way for future analyses to unveil their role during the parasite development and interaction with its intermediate host.