Confronting risks of mirror life.

Broad discussion is needed to chart a path forward.

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

is a colonial marine hydroid that shows 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 species, and , placing them in a comparative evolutionary framework with other cnidarian genomes. We also generated and annotated a single-cell transcriptomic atlas for adult male and identified cell-type markers for all major cell types, including key i-cell markers.

The genome of the colonial hydroid reveals their stem cells utilize a toolkit of evolutionarily shared genes with all animals.

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 species, and , placing them in a comparative evolutionary framework with other cnidarian genomes. We also generated and annotated a single-cell transcriptomic atlas for adult male and identified cell type markers for all major cell types, including key i-cell markers.

Cnidofest 2022: hot topics in cnidarian research.

The second annual Cnidarian Model Systems Meeting, aka "Cnidofest", took place in Davis, California from 7 to 10th of September, 2022. The meeting brought together scientists using cnidarians to study molecular and cellular biology, development and regeneration, evo-devo, neurobiology, symbiosis, physiology, and comparative genomics. The diversity of topics and species represented in presentations highlighted the importance and versatility of cnidarians in addressing a wide variety of biological questions.

Parallels and contrasts between the cnidarian and bilaterian maternal-to-zygotic transition are revealed in Hydractinia embryos.

Embryogenesis requires coordinated gene regulatory activities early on that establish the trajectory of subsequent development, during a period called the maternal-to-zygotic transition (MZT). The MZT comprises transcriptional activation of the embryonic genome and post-transcriptional regulation of egg-inherited maternal mRNA. Investigation into the MZT in animals has focused almost exclusively on bilaterians, which include all classical models such as flies, worms, sea urchin, and vertebrates, thus limiting our capacity to understand the gene regulatory paradigms uniting the MZT across all animals.

Parallels and contrasts between the cnidarian and bilaterian maternal-to-zygotic transition are revealed in embryos.

Embryogenesis requires coordinated gene regulatory activities early on that establish the trajectory of subsequent development, during a period called the maternal-to-zygotic transition (MZT). The MZT comprises transcriptional activation of the embryonic genome and post-transcriptional regulation of egg-inherited maternal mRNA. Investigation into the MZT in animals has focused almost exclusively on bilaterians, which include all classical models such as flies, worms, sea urchin, and vertebrates, thus limiting our capacity to understand the gene regulatory paradigms uniting the MZT across all animals.

XY sex determination in a cnidarian.

Background: Sex determination occurs across animal species, but most of our knowledge about its mechanisms comes from only a handful of bilaterian taxa. This limits our ability to infer the evolutionary history of sex determination within animals.

Results: In this study, we generated a linkage map of the genome of the colonial cnidarian Hydractinia symbiolongicarpus and used it to demonstrate that this species has an XX/XY sex determination system.

Cryopreservation of Sperm to Support Community-Based Repository Development for Preservation of Genetic Resources.

Hydractinia symbiolongicarpus is an emerging model organism in which cutting-edge genomic tools and resources are being developed for use in a growing number of research fields. One limitation of this model system is the lack of long-term storage for genetic resources. The goal of this study was to establish a generalizable cryopreservation approach for Hydractinia that would support future repository development for other cnidarian species.

A family of unusual immunoglobulin superfamily genes in an invertebrate histocompatibility complex.

Most colonial marine invertebrates are capable of allorecognition, the ability to distinguish between themselves and conspecifics. One long-standing question is whether invertebrate allorecognition genes are homologous to vertebrate histocompatibility genes. In the cnidarian allorecognition is controlled by at least two genes, () and (), which encode highly polymorphic cell-surface proteins that serve as markers of self.

Cell Aggregation Assays for Homophilic Interactions Between Cell Surface Proteins.

Many proteins expressed on the cellular surface provide signaling and cell adhesion properties required for vital cellular functions. These binding interactions can occur between different but complementary proteins such as a ligand and receptor, or between the same protein acting as both ligand and receptor. The cell aggregation assay is a straightforward technique to identify homophilic interactions from such proteins.

The Hydractinia allorecognition system.

Hydractinia symbiolongicarpus is a colonial hydroid and a long-standing model system for the study of invertebrate allorecognition. The Hydractinia allorecognition system allows colonies to discriminate between their own tissues and those of unrelated conspecifics that co-occur with them on the same substrate. This recognition mediates spatial competition and mitigates the risk of stem cell parasitism.

New binding specificities evolve via point mutation in an invertebrate allorecognition gene.

Many organisms use genetic self-recognition systems to distinguish themselves from conspecifics. In the cnidarian, , self-recognition is partially controlled by (). encodes a highly polymorphic transmembrane protein that discriminates self from nonself by binding to other Alr2 proteins with identical or similar sequences.

Zinc protection of fertilized eggs is an ancient feature of sexual reproduction in animals.

One of the earliest and most prevalent barriers to successful reproduction is polyspermy, or fertilization of an egg by multiple sperm. To prevent these supernumerary fertilizations, eggs have evolved multiple mechanisms. It has recently been proposed that zinc released by mammalian eggs at fertilization may block additional sperm from entering.

PIRs mediate innate myeloid cell memory to nonself MHC molecules.

Immunological memory specific to previously encountered antigens is a cardinal feature of adaptive lymphoid cells. However, it is unknown whether innate myeloid cells retain memory of prior antigenic stimulation and respond to it more vigorously on subsequent encounters. In this work, we show that murine monocytes and macrophages acquire memory specific to major histocompatibility complex I (MHC-I) antigens, and we identify A-type paired immunoglobulin-like receptors (PIR-As) as the MHC-I receptors necessary for the memory response.

The colonial cnidarian .

, a genus of colonial marine cnidarians, has been used as a model organism for developmental biology and comparative immunology for over a century. It was this animal where stem cells and germ cells were first studied. However, protocols for efficient genetic engineering have only recently been established by a small but interactive community of researchers.

Invertebrate allorecognition.

Most colonial marine invertebrates live as surface encrustations in benthic environments. As they grow, these animals frequently encounter other members of their own species. These encounters typically lead to conflict, in which the colonies aggressively compete for space, or co-existence, in which the colonies peacefully border each other.

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

Background: Hydractinia 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.

Results: Here, we report the use of CRISPR/Cas9 genome editing to generate targeted genomic insertions in H.

Donor SIRPα polymorphism modulates the innate immune response to allogeneic grafts.

Mice devoid of T, B, and natural killer (NK) cells distinguish between self and allogeneic nonself despite the absence of an adaptive immune system. When challenged with an allograft, they mount an innate response characterized by accumulation of mature, monocyte-derived dendritic cells (DCs) that produce interleukin-12 and present antigen to T cells. However, the molecular mechanisms by which the innate immune system detects allogeneic nonself to generate these DCs are not known.

A gut response.

Unexpected findings from the immune system of sea urchin larvae potentially provide insights into immune signaling in ancestral animals.

Allorecognition proteins in an invertebrate exhibit homophilic interactions.

Sessile colonial invertebrates-animals such as sponges, corals, bryozoans, and ascidians-can distinguish between their own tissues and those of conspecifics upon contact [1]. This ability, called allorecognition, mediates spatial competition and can prevent stem cell parasitism by ensuring that colonies only fuse with self or close kin. In every taxon studied to date, allorecognition is controlled by one or more highly polymorphic genes [2-8].

Two unique human decidual macrophage populations.

Several important events occur at the maternal-fetal interface, including generation of maternal-fetal tolerance, remodeling of the uterine smooth muscle and its spiral arteries and glands, and placental construction. Fetal-derived extravillous trophoblasts come in direct contact with maternal decidual leukocytes. Macrophages represent ∼20% of the leukocytes at this interface.

Model systems of invertebrate allorecognition.

Nearly all colonial marine invertebrates are capable of allorecognition--the ability to distinguish between self and genetically distinct members of the same species. When two or more colonies grow into contact, they either reject each other and compete for the contested space or fuse and form a single, chimeric colony. The specificity of this response is conferred by genetic systems that restrict fusion to self and close kin.

Hydractinia allodeterminant alr1 resides in an immunoglobulin superfamily-like gene complex.

Allorecognition, the ability to discriminate between self and nonself, is ubiquitous among colonial metazoans and widespread among aclonal taxa. Genetic models for the study of allorecognition have been developed in the jawed vertebrates, invertebrate chordate Botryllus, and cnidarian Hydractinia. In Botryllus, two genes contribute to the histocompatibility response, FuHC and fester.

HLA-G homodimer-induced cytokine secretion through HLA-G receptors on human decidual macrophages and natural killer cells.

Human decidual CD14(+) macrophages and CD56(+) NK cells were isolated from material obtained after first-trimester pregnancy terminations. Each cell type expressed a specific surface receptor for histocompatibility leukocyte antigen (HLA)-G (an MHC class Ib protein that is expressed on extravillous trophoblasts), LILRB1 on CD14(+) macrophages and KIR2DL4 on CD56(+) NK cells. Cross-linking with anti-LILRB1 or anti-KIR2DL4 resulted in up-regulation of a small subset of mRNAs including those for IL-6, IL-8, and TNFalpha detected using a microarray representing 114 cytokines.