Biology subjects

Frank, U.

Publications and source records attributed to Frank, U..

11 recordsLinked to original sources

bioRxiv2025

An unexpected mode of whole-body regeneration from reaggregated cell suspension in Hydractinia (Cnidaria, Hydrozoa)

Hydrozoan cnidarians are among the few animals that can regenerate whole bodies from reaggregated cell dissociations but the cellular and molecular mechanisms that control this ability and how it is related to embryonic development are not well understood. Furthermore, the evolution of this type of regeneration is enigmatic since it does not occur naturally. Here, we show that aggregate regeneration in Hydractinia symbiolongicarpus proceeds through several, consistent stages that include the formation of an epidermal layer, followed by migration, proliferation, and differentiation of adult pluripotent stem cells, known as i-cells. Migration of i-cells is controlled by sphingosine-1-phosphate signaling. Single-cell transcriptomics revealed, surprisingly, that the newly regenerated individual derives nearly exclusively from i-cell progeny rather than from recycled somatic cells, as seen in other hydrozoans. Given the similarity of this phenomenon to embryogenesis, we propose that the ability of Hydractinia cell aggregates to regenerate is a side effect of the animals i-cell-mediated development.

developmental biology↗

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↗

bioRxiv2024

A positive feedback loop between germ cells and gonads induces and maintains cnidarian sexual reproduction

The fertile gonad includes cells of two distinct developmental origins: the somatic mesoderm and the germline. How somatic and germ cells interact to develop and maintain fertility is not well understood. Here, using grafting experiments and transgenic reporter animals, we find that a specific part of the gonad-the germinal zone-acts as a sexual organizer to induce and maintain de novo germ cells and somatic gonads in non-sexual tissue in the cnidarian Hydractinia symbiolongicarpus. We further show that germ cells express a novel member of the TGF-{beta} family (Gonadless, Gls) that induces somatic gonad morphogenesis. Loss of Gls resulted in animals lacking somatic gonadal structures but having few, non-proliferative germ cells. We propose a model according to which a small number of primary germ cells drive gonad development though Gls morphogen secretion. The germinal zone in the newly formed gonad, in turn, provides positive feedback to induce secondary germ cells by activating Tfap2 (the master regulator of germ cell fate) in resident pluripotent stem cells. De novo induction of germ cells by gonads in adult life is absent in bilaterians with a sequestered germline. However, the contribution of germ cell signaling to the patterning of somatic gonadal tissue, as observed in Hydractinia, may be a general animal feature.

developmental biology↗

bioRxiv2023

The genome of the colonial hydroid Hydractinia reveals their stem cells use a toolkit of genes shared with all animals

Hydractinia is a colonial marine hydroid that exhibits remarkable biological properties, including the capacity to regenerate its entire body throughout its lifetime, a process made possible by its adult migratory stem cells, known as i-cells. Here, we provide an in-depth characterization of the genomic structure and gene content of two Hydractinia species, H. symbiolongicarpus and H. echinata, placing them in a comparative evolutionary framework with other cnidarian genomes. We also generated and annotated a single-cell transcriptomic atlas for adult male H. symbiolongicarpus and identified cell type markers for all major cell types, including key i-cell markers. Orthology analyses based on the markers revealed that Hydractinias i-cells are highly enriched in genes that are widely shared amongst animals, a striking finding given that Hydractinia has a higher proportion of phylum-specific genes than any of the other 41 animals in our orthology analysis. These results indicate that Hydractinias stem cells and early progenitor cells may use a toolkit shared with all animals, making it a promising model organism for future exploration of stem cell biology and regenerative medicine. The genomic and transcriptomic resources for Hydractinia presented here will enable further studies of their regenerative capacity, colonial morphology, and ability to distinguish self from non-self.

genomics↗

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

Pluripotent, germ cell competent adult stem cells underlie cnidarian plant-like life history

In most animals, pluripotency is irreversibly lost post-gastrulation. By this stage, all embryonic cells have already committed either to one of the somatic lineages (ectoderm, endoderm, mesoderm) or to the germline. The lack of pluripotent cells in adult life may be linked to organismal aging. Cnidarians (corals, and jellyfish) are an early branch of animals that do not succumb to age, but the developmental potential of their adult stem cells remains unclear. Here, we show that adult stem cells in the cnidarian Hydractinia symbiolongicarpus (known as i-cells) are pluripotent. We transplanted single i-cells from transgenic fluorescent donors to wild type recipients and followed them in vivo in the translucent animals. Single engrafted i-cells self-renewed and contributed to all somatic lineages and to gamete production, co-existing with and eventually displacing the allogeneic recipients cells. Hence, a fully functional, sexually competent individual can originate from a single adult i-cell. Given that some of their cells remain pluripotent beyond embryogenesis and throughout life, we conclude that Hydractinia embryos never complete gastrulation. Pluripotent i-cells underlie a regenerative, plant-like life history in these animals.

developmental 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

Senescence-induced cellular reprogramming drives cnidarian whole-body regeneration

Cell fate stability is essential to maintaining law and order in complex animals. However, high stability comes at the cost of reduced plasticity and, by extension, poor regenerative ability. This evolutionary trade-off has resulted in most modern animals being rather simple and regenerative or complex and non-regenerative. The mechanisms mediating cellular plasticity and allowing for regeneration remain unknown. We show that signals emitted by senescent cells can destabilize the differentiated state of neighboring somatic cells, reprogramming them into stem cells that are capable of driving whole-body regeneration in the cnidarian Hydractinia symbiolongicarpus. Pharmacological or genetic inhibition of senescence prevented reprogramming and regeneration. Conversely, induction of transient ectopic senescence in a regenerative context resulted in supernumerary stem cells and faster regeneration. We propose that senescence signaling is an ancient mechanism mediating cellular plasticity. Understanding the senescence environment that promotes cellular reprogramming could provide a new avenue to enhance regeneration.

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↗

bioRxiv2021

Hydrozoan sperm-specific H2B histone variants stabilize chromatin and block transcription without enhancing chromatin condensation

Many animals achieve sperm chromatin compaction and stabilisation during spermatogenesis by replacing canonical histones with sperm nuclear basic proteins (SNBPs) such as protamines. A number of animals including hydrozoan cnidarians and echinoid sea urchins lack protamines and have instead evolved a distinctive family of sperm-specific histone H2Bs (spH2Bs) with extended N-termini rich in SPKK-related motifs. Sperm packaging in echinoids such as sea urchins is regulated by spH2Bs and their sperm is negatively buoyant for fertilization on the sea floor. Hydroid cnidarians also package sperm with spH2Bs but undertake broadcast spawning and their sperm properties are poorly characterised. We show that sperm chromatin from the hydroid Hydractinia possesses higher stability than its somatic equivalent, with reduced accessibility of sperm chromatin to transposase Tn5 integration in vivo and to endonucleases in vitro. However, nuclear dimensions are only moderately reduced in mature Hydractinia sperm compared to other cell types. Ectopic expression of spH2B in the background of H2B knockdown resulted in downregulation of global transcription and cell cycle arrest in embryos without altering their nuclear density. Taken together, spH2B variants containing SPKK-related motifs act to stabilise chromatin and silence transcription in Hydractinia sperm without significant chromatin compaction. This is consistent with a contribution of spH2B to sperm buoyancy as a reproductive adaptation.

developmental biology↗

bioRxiv2018

CRISPR/Cas9-mediated gene knockin in the hydroid Hydractinia symbiolongicarpus

BackgroundHydractinia symbiolongicarpus, a colonial cnidarian, is a tractable model system for many cnidarian-specific and general biological questions. Until recently, tests of gene function in Hydractinia have relied on laborious forward genetic approaches, randomly integrated transgenes, or transient knockdown of mRNAs.\n\nResultsHere, we report the use of CRISPR/Cas9 genome editing to generate targeted genomic insertions in H. symbiolonigcarpus. We used CRISPR/Cas9 to promote homologous recombination of two fluorescent reporters, eGFP and tdTomato, into the Eukaryotic elongation factor 1 alpha (Eef1a) locus. We demonstrate that the transgenes are expressed ubiquitously and are stable over two generations of breeding. We further demonstrate that CRISPR/Cas9 genome editing can be used to mark endogenous proteins with FLAG or StrepII-FLAG affinity tags to enable in vivo and ex vivo protein studies.\n\nConclusionsThis is the first account of CRISPR/Cas9 mediated knockins in Hydractinia and the first example of the germline transmission of a CRISPR/Cas9 inserted transgene in a cnidarian. The ability to precisely insert exogenous DNA into the Hydractinia genome will enable sophisticated genetic studies and further development of functional genomics tools in this understudied cnidarian model.

molecular biology↗