One focus of the network has been on the evolution of neurons and nervous systems. Based on extensive scRNA-seq and in situ sequencing data, we established a cell type atlas of the sea lamprey brain. By comparing this dataset to neural data from other vertebrates we revealed an ancestral vertebrate cell type complement. We also looked into the nervous systems of invertebrate species. We used scRNA-seq to unravel the neuronal diversity in sea urchin larva. We found that a subset of the sea urchin neurons show genetic similarities with vertebrate endocrine pancreatic cells, suggesting a common evolutionary origin. For the marine annelid Platynereis, we found that the mushroom bodies have sensory properties and that they resemble the vertebrate telencephalon by molecular anatomy. We have also characterized the ciliomotor neuron type in Platynereis by combining single-cell atlas analysis and functional studies. We explored the diversity of the neuronal populations in cnidarians by looking into a single cell atlas of the Clytia hemisphaerica adult medusa, we found a higher level of differentiated neural cell types than previously described. We have also characterized neuron diversity in the arthropod clade, which was assessed by doing sc-RNAseq in the spider Parasteatoda tepidariorum. We profiled embryos at a developmental stage marked by the beginning of brain differentiation and found nervous system-patterning genes that had never been described in spiders before. Altogether, this pioneering work opens up for exploring the diversification of neurons and nervous systems during evolution.
Another focus has been on regeneration. We examined the fidelity of Parhyale hawaiensis leg regeneration. We found that regenerated legs are precise replicates. Single-nuclei RNA seq showed that regenerated and uninjured legs are indistinguishable in terms of cell type composition. Also, by comparing the global transcriptional dynamics of leg regeneration and development in Parhyale we showed that these two processes show distinct temporal profiles of gene expression. Related to this, we investigated the role of piRNAs and PIWI proteins in stem cell maintenance, differentiation and cancer. We developed a bioinformatics tool to identify and annotate somatic piRNAs and used it to identify the piRNA complement in: sea urchin P. lividus embryos, differentiating cardiomyocytes and in colon-rectal cancer (CRC) cell lines. Also, we have characterized the activity of the PIWI/piRNA pathway in CRC cells and found that it may contribute to the establishment and/or maintenance of clinicopathological features of colon cancer.
In addition, we were interested in the life cycle of marine invertebrates and how the cell type complements change between larval and adult stages. We generated single cell expression atlases of different developmental stages in diverse organisms and defined stage-specific and common cell types. For the planula and medusa stages in Clytia hemisphaerica we found both: cells, with unique transcriptional programs, and cell types with conserved gene expression programs between both stages. We could detect shared elements in the transcriptional signature between neural cells and mature nematocytes, allowing us to propose evolutionary scenarios about their emergence. Also, intending to reconstruct the evolution of the neural and secretory cell types at the aboral end of the cnidarian planula larva, we compared Clytia and the stony coral Pocillopora acuta. Also, we aimed to identify potential homologous cellular lineages in two species of Lophotrochozoan larvae.
The results of our research were published in high-impact peer-reviewed scientific journals and were presented at prestigious international conferences. Also, we organized several outreach activities to disseminate the results of our research to the general public.
