Biology subjects

Salinas-Saavedra, M.

Publications and source records attributed to Salinas-Saavedra, M..

7 recordsLinked to original sources

bioRxiv2024

The Hydractinia cell atlas reveals cellular and molecular principles of cnidarian coloniality

Coloniality is a widespread growth form in cnidarians, tunicates, and bryozoans, among others. Despite being modular, composed of multiple zooids and supporting tissues, colonies function as a single physiological unit. A major question in the biology of colonies is the cellular mechanism of generating structurally and functionally distinct colony parts. The cnidarian Hydractinia establishes colonies with different types of zooids (polyps), interconnected by a gastrovascular system that is attached to the substrate and known as stolons. We obtained single cell transcriptomic profiles of [~]200K Hydractinia cells, including isolated stolons and two polyp types. We characterised the major Hydractinia cell types and quantified their abundance across colony parts. Overall, we find that distinct colony parts are characterised primarily by distinct combinations of shared cell types and to a lesser extent by part-specific cell types. Therefore, we propose that both cell type combinations, as well as rarer cell type innovations, have been the main mechanism in the evolution of coloniality in cnidarians. We identified cell type-specific transcription factors (TFs) and gene networks expressed within these cell types. Notably, we discovered a previously unidentified, stolon-specific cell type, which expresses enzymes related to biomineralization and chitin synthesis, reminiscent of molluscan shell matrix proteins that may represent a crucial adaptation to the animals habitat. In summary, the Hydractinia cell atlas elucidates the fundamental cellular and molecular mechanisms underlying coloniality.

systems biology↗

bioRxiv2022

A pan-cnidarian microRNA is an ancient biogenesis regulator of stinging cells

An ancient evolutionary innovation of a novel cell-type, the stinging cell (cnidocyte), appeared >600 million years ago in the phylum Cnidaria (sea anemones, corals, hydroids, and jellyfish). A complex bursting nano-injector of venom, the cnidocyst, is embedded in cnidocytes and enables cnidarians paralyzing prey and predators, contributing to this phylums evolutionary success. In this work, we show that post-transcriptional regulation by a pan-cnidarian microRNA, miR-2022, is essential for biogenesis of these cells. By manipulation of miR-2022 levels in a transgenic reporter line of cnidocytes in the sea anemone Nematostella vectensis, followed by transcriptomics, single-cell data analysis, prey paralysis assays, and cell sorting of transgenic cnidocytes, we reveal that miR-2022 enables cnidocyte biogenesis, while exhibiting a conserved expression domain with its targets in cnidocytes of other cnidarian species. Thus, here we reveal one of natures most ancient microRNA-regulated processes by studying the functional basis for its conservation.

evolutionary biology↗

bioRxiv2022

Randomly incorporated genomic 6mA delays zygotic transcription initiation

N6-methyldeoxyadenosine (6mA) is a chemical alteration of DNA, observed across all realms of life. The functions of 6mA are well understood in bacteria but its roles in animal genomes have been controversial. We show that 6mA randomly accumulates in early embryos of the cnidarian Hydractinia symbiolongicarpus, with a peak at the 16-cell stage followed by clearance to background levels two cell cycles later, at the 64-cell stage - the embryonic stage at which zygotic genome activation occurs in this animal. Knocking down Alkbh1, a putative initiator of animal 6mA clearance, resulted in higher levels of 6mA at the 64-cell stage and a delay in the commencement of zygotic transcription. Our data are consistent with 6mA originating from recycled nucleotides of degraded m6A-marked maternal RNA post-fertilization. Therefore, while 6mA does not function as an epigenetic mark in Hydractinia, its random incorporation into the early embryonic genome inhibits transcription. Alkbh1 functions as a genomic 6mA cleaner, facilitating timely zygotic genome activation. Given the random nature of genomic 6mA accumulation and its ability to interfere with gene expression, defects in 6mA clearance may represent a hitherto unknown cause of various pathologies.

developmental biology↗

bioRxiv2022

A cellular and molecular analysis of SoxB-driven neurogenesis in a cnidarian

Neurogenesis is the generation of neurons from stem cells, a process that is regulated by SoxB transcription factors (TFs) in many animals. Although the roles of these TFs are well understood in bilaterians, how their neural function evolved is unclear. Here, we use Hydractinia symbiolongicarpus, a member of the early-branching phylum Cnidaria, to provide insight into this question. Using a combination of mRNA in situ hybridization, transgenesis, gene knockdown, transcriptomics, and in-vivo imaging, we provide a comprehensive molecular and cellular analysis of neurogenesis during embryogenesis, homeostasis, and regeneration in this animal. We show that SoxB genes act sequentially. Stem cells expressing Piwi1 and Soxb1, which have a broad developmental potential, become neural progenitors that express Soxb2 before differentiating into mature neural cells. Knockdown of SoxB genes resulted in complex defects in embryonic neurogenesis. Hydractinia neural cells differentiate while migrating from the aboral to the oral end of the animal, but it is unclear whether migration per se or exposure to different microenvironments is the main driver of their fate determination. Our data constitute a rich resource for studies aiming at addressing this question, which is at the heart of understanding neurological disorders in all animals, including humans.

developmental biology↗

bioRxiv2019

β-catenin has an ancestral role in cell fate specification but not cell adhesion

The {beta}-catenin protein has two major known functions in animal cells. It keeps epithelial tissue homeostasis by its connection with Adherens Junctions (AJ), and it serves as a transcriptional cofactor along with Lef/Tcf to enter the nucleus and regulate target genes of the Wnt/{beta}-catenin (cWnt) signaling pathway. To assess the ancestral role of {beta}-catenin during development we examined its distribution and function in the ctenophore Mnemiopsis leidyi (one of the earliest branching animal phyla) by using ctenophore-specific antibodies and mRNA injection. We found that {beta}-catenin protein never localizes to cell-cell contacts during embryogenesis as it does in other metazoans, most likely because ctenophore-cadherins do not have the cytoplasmic domain required for interaction with the catenin proteins. Downregulation of zygotic Ml{beta}-catenin signaling led to the loss of endodermal and mesodermal tissues indicating that nuclear {beta}-catenin may have a deep role in germ-layer evolution. Our results indicate that the ancestral role for {beta}-catenin was in the cell-fate specification and not in cell adhesion and also further emphasizes the critical role of this protein in the evolution of tissue layers in metazoans.

developmental biology↗

bioRxiv2018

Par-Cteno-Genesis or Cteno Par-Genesis

In bilaterians and cnidarians, embryonic and epithelial cell-polarity are regulated by the interactions between Par proteins, Wnt/PCP signaling pathway, and cell-cell adhesion. Par proteins are highly conserved across Metazoa, including ctenophores. But strikingly, ctenophore genomes lack components of the Wnt/PCP pathway and cell-cell adhesion complexes; raising the question if ctenophore cells are polarized by mechanisms involving Par proteins. Here, by using immunohistochemistry and live-cell imaging overexpression of specific mRNAs, we describe for the first time the subcellular localization of selected Par proteins in blastomeres and epithelial cells during the embryogenesis of the ctenophore Mnemiopsis leidyi. We show that these proteins distribute differently compared to what has been described for other animals, even though they segregate in a host-specific fashion when expressed in cnidarian embryos. This differential localization might be related to the emergence of different junctional complexes during metazoan evolution. Data obtained here challenge the ancestry of the apicobasal cell polarity and raise questions about the homology of epithelial tissue across the Metazoa.

developmental biology↗

bioRxiv2017

Germ layer specific regulation of cell polarity and adhesion: insight into the evolution of mesoderm

In triploblastic animals, Par-proteins regulate cell-polarity and adherens junctions of both ectodermal and endodermal epithelia. But, in embryos of the diploblastic cnidarian Nematostella vectensis, Par-proteins are degraded in all cells in the bifunctional gastrodermal epithelium. Using immunohistochemistry, CRISPR/Cas9 mutagenesis, and overexpression of specific mRNAs, we describe the functional association between Par-proteins, {beta}-catenin, and snail transcription factor genes in N. vectensis embryos. We demonstrate that the aPKC/Par complex regulates the localization of {beta}-catenin in the ectoderm by stabilizing its role in cell-adhesion, and that endomesodermal epithelial cells are organized by a different cell-adhesion system than that of overlying ectoderm. We also show that ectopic expression of snail genes, which are expressed in mesodermal derivatives in bilaterians, are sufficient to downregulate Par-proteins and translocate {beta}-catenin from the junctions to the cytoplasm in ectodermal cells. These data provide molecular insight into the evolution of epithelial structure and distinct mesodermal tissue in metazoan embryos.

developmental biology↗