Biology subjects

Paganos, P.

Publications and source records attributed to Paganos, P..

8 recordsLinked to original sources

bioRxiv2026

Evolutionary landscapes of zygotic genome activation across animals

During early animal embryogenesis, gene expression control shifts from maternally deposited products to newly transcribed RNA through zygotic genome activation (ZGA). Although essential and universal, ZGA remains poorly understood outside a few model species. Here, we generated a transcriptomic atlas of early embryogenesis across 61 animal species from 13 phyla and used a unified computational framework to infer ZGA timing systematically. We find extensive variation in ZGA onset across animals, but show that the ratio between genome size and egg cytoplasmic volume, a proxy for the nuclear-to-cytoplasmic ratio, robustly predicts when genome activation begins. We also reveal that zygotic genes also differ from maternal transcripts in genomic architecture, function and evolutionary conservation, suggesting that ZGA follows a conserved molecular logic despite flexible transcriptomic outputs.

evolutionary biology↗

bioRxiv2025

Single Nucleus Profiling Highlights the All-Brain Echinoderm Nervous System

Metazoans comprise diverse tissues and cell types, each essential for the survival of the organism. Most of these cell types are established early in embryogenesis and persist into adulthood. However, in indirectly developing sea urchins, the continuity between embryonic and adult stages is thus interrupted by a planktonic larval stage that undergoes complete metamorphosis. In addition, while the gene regulatory networks governing distinct embryonic and larval cell lineages are well studied, the molecular and morphological identities of post-metamorphic sea urchin cell types remain poorly understood. Here, we reconstructed the cell type atlas of post-metamorphic Paracentrotus lividus juveniles using single-nucleus transcriptomics, shedding light on the conservation of genetic regulatory mechanisms in post-metamorphic cell types. We identified cell signatures corresponding to eight distinct cell type groups and analyzed at least twenty-nine neuronal cell families, including fifteen unique photoreceptor cell signatures. By combining single cell transcriptomics with spatial gene expression analysis and high-resolution electron microscopy, we identified homologues of vertebrate neuronal genes and photoreceptive opsins expressed throughout the sea urchin body. These findings provide evidence that the echinoderm body plan is not only predominantly head-like, but also exhibits an all-brain organization in an animal previously considered to have a primitive nervous system.

evolutionary biology↗

bioRxiv2025

Molecular evidence for pre-chordate origins of ovarian cell types and neuroendocrine control of reproduction

Sexual reproduction in animals requires the development of oocytes, or egg cells. This process, termed oogenesis, requires complex interactions amongst germline and somatic cell types in the ovary. How did these cell types and their signaling interactions evolve? Here we use the sea star Patiria miniata as a non-chordate deuterostome representative to define the ovarian cell type toolkit in echinoderms. Sea stars continuously produce millions of new oocytes throughout their lifespan, making them a practical system to understand the mechanisms that drive oogenesis from a biomedical and evolutionary perspective. We performed scRNA-seq combined with high-resolution 3D-imaging to reveal the ovarian cell types and their spatial organization. Our data support the presence of actively dividing oogonial stem cells and granulosa-like and theca-like cells, which display similarities and possible homology with their mammalian counterparts. Lastly, our data support the existence of an endocrine signaling system between oogonial stem cells and intrinsic ovarian neurons with striking similarities to the vertebrate hypothalamic-pituitary-gonadal axis. Overall, this study provides molecular evidence supporting the possible pre-chordate origins of conserved ovarian cell types, and the presence of an intrinsic neuroendocrine system which potentially controls oogenesis and predates the formation of the hypothalamic-pituitary-gonadal axis in vertebrates.

evolutionary biology↗

bioRxiv2024

Deep conservation of cis-regulatory elements and chromatin organization in echinoderms uncover ancestral regulatory features of animal genomes

Despite the growing abundance of sequenced animal genomes, we only have detailed knowledge of regulatory organization for a handful of lineages, particularly flies and vertebrates. These two groups of taxa show contrasting trends in the molecular mechanisms of 3D chromatin organization and long-term evolutionary dynamics of cis-regulatory element (CREs) conservation. To help us identify shared versus derived features that could be responsible for the evolution of these different regulatory architectures in animals, we studied the evolution and organization of the regulatory genome of echinoderms, a lineage whose phylogenetic position and relatively slow molecular evolution has proven particularly useful for evolutionary studies. First, using PacBio and HiC data, we generated new reference genome assemblies for two species belonging to two different echinoderm classes: the purple sea urchin Strongylocentrotus purpuratus and the bat sea star Patiria miniata. Second, we characterized their 3D chromatin architecture, identifying TAD-like domains in echinoderms that, like in flies, do not seem to be associated with CTCF motif orientation. Third, we systematically profiled CREs during sea star and sea urchin development using ATAC-seq, comparing their regulatory logic and dynamics over multiple developmental stages. Finally, we investigated sea urchin and sea star CRE evolution across multiple evolutionary distances and timescales, from closely related species to other echinoderm classes and deuterostome lineages. This showed the presence of several thousand elements conserved for hundreds of millions of years, revealing a vertebrate-like pattern of CRE evolution that probably constitutes an ancestral property of the regulatory evolution of animals.

evolutionary biology↗

bioRxiv2024

Developmental toxicity of pre-production plastic pellets affects a large swathe of invertebrate taxa

Microplastics pose risks to marine organisms through ingestion, entanglement, and as carriers of toxic additives and environmental pollutants. Plastic pre-production pellet leachates have been shown to affect the development of sea urchins and, to some extent, mussels. The extent of those developmental effects on other animal phyla remains unknown. Here, we test the toxicity of environmental mixed nurdle samples and new PVC pellets for the embryonic development or asexual reproduction by regeneration of animals from all the major animal superphyla (Lophotrochozoa, Ecdysozoa, Deuterostomia and Cnidaria). Our results show diverse, concentration-dependent impacts in all the species sampled for new pellets, and for molluscs and deuterostomes for environmental samples. Embryo axial formation, cell specification and, specially, morphogenesis seem to be the main processes affected by plastic leachate exposure. Our study serves as a proof of principle for the potentially catastrophic effects that increasing plastic concentrations in the oceans and other ecosystems can have across animal populations from all major animal superphyla.

developmental biology↗

bioRxiv2023

An integrative multi-omics approach to draft gene regulatory networks at a cell type resolution

Drafting gene regulatory networks (GRNs) requires embryological knowledge pertaining to the cell type families, information on the regulatory genes, causal data from gene knockdown experiments and validations of the identified interactions by cis-regulatory analysis. We use multi-omics involving next-generation sequencing (-seq) to obtain the necessary information drafting the sea urchin posterior gut GRN. Here we present an update to the GRN using i) a single cell RNA-seq derived cell atlas highlighting the 2 day post fertilization (dpf) sea urchin gastrula cell type families, as well as the genes expressed at single cell level, ii) a set of putative cis-regulatory modules and transcription factor (TF) binding sites obtained from chromatin accessibility ATAC-seq data, and iii) interactions directionality obtained from differential bulk RNA-seq following knockdown of the TF Sp-Pdx1, a key regulator of gut patterning in sea urchins. Combining these datasets, we draft the GRN for the hindgut Sp-Pdx1 positive cells in the 2 dpf gastrula embryo. Overall, our data resolves the complex connectivity of the posterior gut GRN and increases the resolution of gene regulatory cascades operating within it.

developmental biology↗

bioRxiv2021

Single cell RNA sequencing of the Strongylocentrotus purpuratus larva reveals the blueprint of major cell types and nervous system of a non-chordate deuterostome

Identifying the molecular fingerprint of organismal cell types is key for understanding their function and evolution. Here, we use single cell RNA sequencing (scRNA-seq) to survey the cell types of the sea urchin early pluteus larva, representing an important developmental transition from non-feeding to feeding larva. We identify 21 distinct cell clusters, representing cells of the digestive, skeletal, immune, and nervous systems. Further subclustering of these reveal a highly detailed portrait of cell diversity across the larva, including the identification of neuronal cell types. We then validate important gene regulatory networks driving sea urchin development and reveal new domains of activity within the larval body. Focusing on neurons that co-express Pdx-1 and Brn1/2/4, we identify an unprecedented number of genes shared by this population of neurons in sea urchin and vertebrate endocrine pancreatic cells. Using differential expression results from Pdx-1 knockdown experiments, we show that Pdx1 is necessary for the acquisition of the neuronal identity of these cells. We hypothesize that a network similar to the one orchestrated by Pdx1 in the sea urchin neurons was active in an ancestral cell type and then inherited by neuronal and pancreatic developmental lineages in sea urchins and vertebrates.

developmental biology↗

bioRxiv2020

Post-metamorphic skeletal growth in the sea urchin Paracentrotus lividus and implications for body plan evolution

Understanding the molecular and cellular processes that underpin animal development are crucial for understanding the diversity of body plans found on the planet today. Because of their abundance in the fossil record, and tractability as a model system in the lab, skeletons provide an ideal experimental model to understand the origins of animal diversity. We herein use molecular and cellular markers to understand the growth and development of the juvenile sea urchin (echinoid) skeleton. We developed a detailed staging scheme based off of the first [~]four weeks of post-metamorphic life of the regular echinoid Paracentrotus lividus. We paired this scheme with immunohistochemical staining for neuronal, muscular, and skeletal tissues, and fluorescent assays of skeletal growth and cell proliferation to understand the molecular and cellular mechanisms underlying skeletal growth and development of the sea urchin body plan. Our experiments highlight the role of skeletogenic proteins in accretionary skeletal growth and cell proliferation in the addition of new metameric tissues. Furthermore, our work provides a framework for understanding the developmental evolution of sea urchin body plans on macroevolutionary timescales.

developmental biology↗