The mitochondrial protein Sod2 is important for the migration, maintenance, and fitness of germ cells.

To maintain a range of cellular functions and to ensure cell survival, cells must control their levels of reactive oxygen species (ROS). The main source of these molecules is the mitochondrial respiration machinery, and the first line of defense against these toxic substances is the mitochondrial enzyme superoxide dismutase 2 (Sod2). Thus, investigating early expression patterns and functions of this protein is critical for understanding how an organism develops ways to protect itself against ROS and enhance tissue fitness.

Spatial organization and function of RNA molecules within phase-separated condensates are controlled by Dnd1.

Germ granules, condensates of phase-separated RNA and protein, are organelles essential for germline development in different organisms The patterning of the granules and its relevance for germ cell fate are not fully understood. Combining three-dimensional structural and functional analyses, we study the dynamic spatial organization of molecules within zebrafish germ granules. We find that localization of RNA molecules to the periphery of the granules, where ribosomes are localized depends on translational activity at this location.

Linking human Dead end 1 (DND1) variants to male infertility employing zebrafish embryos.

Study Question: Is the vertebrate protein Dead end (DND1) a causative factor for human infertility and can novel in vivo assays in zebrafish help in evaluating this?

Summary Answer: Combining patient genetic data with functional in vivo assays in zebrafish reveals a possible role for DND1 in human male fertility.

What Is Known Already: About 7% of the male population is affected by infertility but linking specific gene variants to the disease is challenging. The function of the DND1 protein was shown to be critical for germ cell development in several model organisms but a reliable and cost-effective method for evaluating the activity of the protein in the context of human male infertility is still missing.

Primordial germ cells adjust their protrusion type while migrating in different tissue contexts in vivo.

In both physiological processes and disease contexts, migrating cells have the ability to adapt to conditions in their environment. As an in vivo model for this process, we use zebrafish primordial germ cells that migrate throughout the developing embryo. When migrating within an ectodermal environment, the germ cells form fewer and smaller blebs when compared with their behavior within mesodermal environment.

A robust and tunable system for targeted cell ablation in developing embryos.

Cell ablation is a key method in the research fields of developmental biology, tissue regeneration, and tissue homeostasis. Eliminating specific cell populations allows for characterizing interactions that control cell differentiation, death, behavior, and spatial organization of cells. Current methodologies for inducing cell death suffer from relatively slow kinetics, making them unsuitable for analyzing rapid events and following primary and immediate consequences of the ablation.

Blebs-Formation, Regulation, Positioning, and Role in Amoeboid Cell Migration.

In the context of development, tissue homeostasis, immune surveillance, and pathological conditions such as cancer metastasis and inflammation, migrating amoeboid cells commonly form protrusions called blebs. For these spherical protrusions to inflate, the force for pushing the membrane forward depends on actomyosin contraction rather than active actin assembly. Accordingly, blebs exhibit distinct dynamics and regulation.

Hand2 delineates mesothelium progenitors and is reactivated in mesothelioma.

The mesothelium lines body cavities and surrounds internal organs, widely contributing to homeostasis and regeneration. Mesothelium disruptions cause visceral anomalies and mesothelioma tumors. Nonetheless, the embryonic emergence of mesothelia remains incompletely understood.

A JAM-A-tetraspanin-αvβ5 integrin complex regulates contact inhibition of locomotion.

Contact inhibition of locomotion (CIL) is a process that regulates cell motility upon collision with other cells. Improper regulation of CIL has been implicated in cancer cell dissemination. Here, we identify the cell adhesion molecule JAM-A as a central regulator of CIL in tumor cells.

AMPK adapts metabolism to developmental energy requirement during dendrite pruning in Drosophila.

To reshape neuronal connectivity in adult stages, Drosophila sensory neurons prune their dendrites during metamorphosis using a genetic degeneration program that is induced by the steroid hormone ecdysone. Metamorphosis is a nonfeeding stage that imposes metabolic constraints on development. We find that AMP-activated protein kinase (AMPK), a regulator of energy homeostasis, is cell-autonomously required for dendrite pruning.

Heading towards a dead end: The role of DND1 in germ line differentiation of human iPSCs.

The DND microRNA-mediated repression inhibitor 1 (DND1) is a conserved RNA binding protein (RBP) that plays important roles in survival and fate maintenance of primordial germ cells (PGCs) and in the development of the male germline in zebrafish and mice. Dead end was shown to be expressed in human pluripotent stem cells (PSCs), PGCs and spermatogonia, but little is known about its specific role concerning pluripotency and human germline development. Here we use CRISPR/Cas mediated knockout and PGC-like cell (PGCLC) differentiation in human iPSCs to determine if DND1 (1) plays a role in maintaining pluripotency and (2) in specification of PGCLCs.

Zebrafish Primordial Germ Cell Migration.

Similar to many other organisms, zebrafish primordial germ cells (PGCs) are specified at a location distinct from that of gonadal somatic cells. Guided by chemotactic cues, PGCs migrate through embryonic tissues toward the region where the gonad develops. In this process, PGCs employ a bleb-driven amoeboid migration mode, characterized by low adhesion and high actomyosin contractility, a strategy used by other migrating cells, such as leukocytes and certain types of cancer cells.

Zebrafish dazl regulates cystogenesis and germline stem cell specification during the primordial germ cell to germline stem cell transition.

Fertility and gamete reserves are maintained by asymmetric divisions of the germline stem cells to produce new stem cells or daughters that differentiate as gametes. Before entering meiosis, differentiating germ cells (GCs) of sexual animals typically undergo cystogenesis. This evolutionarily conserved process involves synchronous and incomplete mitotic divisions of a GC daughter (cystoblast) to generate sister cells connected by intercellular bridges that facilitate the exchange of materials to support rapid expansion of the gamete progenitor population.

Bioorthogonal mRNA labeling at the poly(A) tail for imaging localization and dynamics in live zebrafish embryos.

Live imaging of mRNA in cells and organisms is important for understanding the dynamic aspects underlying its function. Ideally, labeling of mRNA should not alter its structure or function, nor affect the biological system. However, most methods applied make use of genetically encoded tags and reporters that significantly enhance the size of the mRNA of interest.

Chemokine-biased robust self-organizing polarization of migrating cells in vivo.

To study the mechanisms controlling front-rear polarity in migrating cells, we used zebrafish primordial germ cells (PGCs) as an in vivo model. We find that polarity of bleb-driven migrating cells can be initiated at the cell front, as manifested by actin accumulation at the future leading edge and myosin-dependent retrograde actin flow toward the other side of the cell. In such cases, the definition of the cell front, from which bleb-inhibiting proteins such as Ezrin are depleted, precedes the establishment of the cell rear, where those proteins accumulate.

Using migrating cells as probes to illuminate features in live embryonic tissues.

The biophysical and biochemical properties of live tissues are important in the context of development and disease. Methods for evaluating these properties typically involve destroying the tissue or require specialized technology and complicated analyses. Here, we present a novel, noninvasive methodology for determining the spatial distribution of tissue features within embryos, making use of nondirectionally migrating cells and software we termed "Landscape," which performs automatized high-throughput three-dimensional image registration.

E-cadherin focuses protrusion formation at the front of migrating cells by impeding actin flow.

The migration of many cell types relies on the formation of actomyosin-dependent protrusions called blebs, but the mechanisms responsible for focusing this kind of protrusive activity to the cell front are largely unknown. Here, we employ zebrafish primordial germ cells (PGCs) as a model to study the role of cell-cell adhesion in bleb-driven single-cell migration in vivo. Utilizing a range of genetic, reverse genetic and mathematical tools, we define a previously unknown role for E-cadherin in confining bleb-type protrusions to the leading edge of the cell.

Building Relationships: A Role for Innexins in Tissue Formation.

The mechanisms that govern cell interactions during organ formation are not fully understood. In this issue of Developmental Cell, Miao et al. demonstrate a channel-independent role for gap junction proteins in the establishment of contacts between three cell types that build up the micropyle during oocyte development in Drosophila.

Dead end and Detour: The function of the RNA-binding protein Dnd in posttranscriptional regulation in the germline.

Posttranscriptional regulation is a key part of controlling gene expression in different cell types, in particular in the context of specification, maintenance and differentiation of germline cells. A central regulator of these processes is the vertebrate protein Dead end (Dnd). This RNA-binding protein is important for the survival and preservation of the fate of primordial germ cells (PGCs) and for subsequent development of the male germline.

Tracking and line integration of diffuse cellular subdomains by mesh advection.

Active molecular transport ensures a purposeful spatiotemporal distribution of cellular proteins and is therefore key to a wide range of processes such as morphogenesis, homeostasis or migration. However, redistributions of molecules in bulk are seldom quantified because the regions involved are too diffuse to be segmented consistently. To bridge this gap, we propose a Laplace-corrected Runge-Kutta advection that is based on mesh triangulation.

Germ cell migration-Evolutionary issues and current understanding.

In many organisms, primordial germ cells (PGCs) are specified at a different location than where the gonad forms, meaning that PGCs must migrate toward the gonad within the early developing embryo. Following species-specific paths, PGCs can be passively carried by surrounding tissues and also perform active migration. When PGCs actively migrate through and along a variety of embryonic structures in different organisms, they adopt an ancestral robust migration mode termed "amoeboid motility", which allows cells to migrate within diverse environments.

Cellular Blebs and Membrane Invaginations Are Coupled through Membrane Tension Buffering.

Bleb-type cellular protrusions play key roles in a range of biological processes. It was recently found that bleb growth is facilitated by a local supply of membrane from tubular invaginations, but the interplay between the expanding bleb and the membrane tubes remains poorly understood. On the one hand, the membrane area stored in tubes may serve as a reservoir for bleb expansion.

Retention of paternal DNA methylome in the developing zebrafish germline.

Two waves of DNA methylation reprogramming occur during mammalian embryogenesis; during preimplantation development and during primordial germ cell (PGC) formation. However, it is currently unclear how evolutionarily conserved these processes are. Here we characterise the DNA methylomes of zebrafish PGCs at four developmental stages and identify retention of paternal epigenetic memory, in stark contrast to the findings in mammals.