Stat3/Cdc25a-dependent cell proliferation promotes embryonic axis extension during zebrafish gastrulation

The physical roles of different posterior tissues in zebrafish axis elongation

Shaping embryonic tissues requires spatiotemporal changes in genetic and signaling activity as well as in tissue mechanics. Studies linking specific molecular perturbations to changes in the tissue physical state remain sparse. Here we study how specific genetic perturbations affecting different posterior tissues during zebrafish body axis elongation change their physical state, the resulting large-scale tissue flows, and posterior elongation. Using a custom analysis software to reveal spatiotemporal variations in tissue fluidity, we show that dorsal tissues are most fluid at the posterior end, rigidify anterior of this region, and become more fluid again yet further anteriorly. In the absence of notochord (noto mutants) or when the presomitic mesoderm is substantially reduced (tbx16 mutants), dorsal tissues elongate normally. Perturbations of posterior-directed morphogenetic flows in dorsal tissues (vangl2 mutants) strongly affect the speed of elongation, highlighting the essential role of dorsal cell flows in delivering the necessary material to elongate the axis.

Modeling Musculoskeletal Disorders in Zebrafish: Advancements in Muscle and Bone Research

Zebrafish (Danio rerio) have emerged as a valuable model organism for investigating musculoskeletal development and the pathophysiology of associated diseases. Key genes and biological processes in zebrafish that closely mirror those in humans, rapid development, and transparent embryos make zebrafish ideal for the in vivo studies of bone and muscle formation, as well as the molecular mechanisms underlying musculoskeletal disorders. This review focuses on the utility of zebrafish in modeling various musculoskeletal conditions, with an emphasis on bone diseases such as osteoporosis and osteogenesis imperfecta, as well as muscle disorders like Duchenne muscular dystrophy. These models have provided significant insights into the molecular pathways involved in these diseases, helping to identify the key genetic and biochemical factors that contribute to their progression. These findings have also advanced our understanding of disease mechanisms and facilitated the development of potential therapeutic strategies for musculoskeletal disorders.

Differential Sensitivity of Midline Patterning to Mitosis during and after Primitive Streak Extension

Background

Midline establishment is a fundamental process during early embryogenesis for Bilaterians . Midline patterning in nonamniotes can occur without mitosis, through Planar Cell Polarity (PCP) signaling. By contrast, amniotes utilize both cell proliferation and PCP signaling for patterning early midline landmark, the primitive streak (PS). This study examined their roles for midline patterning at post PS-extension.

Results

In contrast to PS extension stages, embryos under mitotic arrest during the post PS-extension preserved notochord (NC) extension and Hensen's node (HN)/PS regression judged by both morphology and marker genes, although they became shorter, and laterality was lost. Remarkably, no or background level of expression was detected for the majority of PCP core components in the NC-HN-PS area at post PS-extension stages, except for robustly detected prickle-1 . Morpholino knockdown of Prickle-1 showed little influence on midline patterning, except for suppressed embryonic growth. Lastly, associated with mitotic arrest-induced size reduction, midline tissue cells displayed hypertrophy.

Conclusion

Thus, the study has identified at least two distinct mitosis sensitivity phases during early midline pattering: One is PS extension that requires both mitosis and PCP, and the other is mitotic arrest-resistant midline patterning with little influence by PCP at post PS-extension stages.

Anti-Cancer Potential of Isoflavone-Enriched Fraction from Traditional Thai Fermented Soybean against Hela Cervical Cancer Cells

Cervical cancer is a leading cause of gynecological malignancies and cancer-related deaths among women worldwide. This study investigates the anti-cancer activity of Thua Nao, a Thai fermented soybean, against HeLa cervical carcinoma cells, and explores its underlying mechanisms. Our findings reveal that the ethyl acetate fraction of Thua Nao (TN-EA) exhibits strong anti-cancer potential against HeLa cells. High-performance liquid chromatography (HPLC) analysis identified genistein and daidzein as the major isoflavones in TN-EA responsible for its anti-cancer activity. TN-EA and genistein reduced cell proliferation and induced G2/M phase arrest, while daidzein induced G1 arrest. These responses were associated with the downregulation of cell cycle regulators, including Cyclin B1, cycle 25C (Cdc25C), and phosphorylated cyclin-dependent kinase 1 (CDK-1), and the upregulation of the cell cycle inhibitor p21. Moreover, TN-EA and its active isoflavones promoted apoptosis in HeLa cells through the intrinsic pathway, evidenced by increased levels of cleaved Poly (ADP-ribose) polymerase (PARP) and caspase-3, loss of mitochondrial membrane potential, and the downregulation of anti-apoptotic proteins B-cell leukemia/lymphoma 2 (Bcl-2), B-cell lymphoma-extra-large (Bcl-xL), cellular inhibitor of apoptosis proteins 1 (cIAP), and survivin. Additionally, TN-EA and its active isoflavones effectively reduced cell invasion and migration by downregulating extracellular matrix degradation enzymes, including Membrane type 1-matrix metalloproteinase (MT1-MMP), urokinase-type plasminogen activator (uPA), and urokinase-type plasminogen activator receptor (uPAR), and reduced the levels of the mesenchymal marker N-cadherin. At the molecular level, TN-EA suppressed STAT3 activation via the regulation of JNK and Erk1/2 signaling pathways, leading to reduced proliferation and invasion of HeLa cells.

Zmiz1 is a novel regulator of lymphatic endothelial cell gene expression and function

Zinc Finger MIZ-Type Containing 1 (Zmiz1), also known as ZIMP10 or RAI17, is a transcription cofactor and member of the Protein Inhibitor of Activated STAT (PIAS) family of proteins. Zmiz1 is critical for a variety of biological processes including vascular development. However, its role in the lymphatic vasculature is unknown. In this study, we utilized human dermal lymphatic endothelial cells (HDLECs) and an inducible, lymphatic endothelial cell (LEC)-specific Zmiz1 knockout mouse model to investigate the role of Zmiz1 in LECs. Transcriptional profiling of ZMIZ1-deficient HDLECs revealed downregulation of genes crucial for lymphatic vessel development. Additionally, our findings demonstrated that loss of Zmiz1 results in reduced expression of proliferation and migration genes in HDLECs and reduced proliferation and migration in vitro. We also presented evidence that Zmiz1 regulates Prox1 expression in vitro and in vivo by modulating chromatin accessibility at Prox1 regulatory regions. Furthermore, we observed that loss of Zmiz1 in mesenteric lymphatic vessels significantly reduced valve density. Collectively, our results highlight a novel role of Zmiz1 in LECs and as a transcriptional regulator of Prox1, shedding light on a previously unknown regulatory factor in lymphatic vascular biology.

Stat3 Regulates Developmental Hematopoiesis and Impacts Myeloid Cell Function via Canonical and Non-Canonical Modalities

INTRODUCTION

Signal transducer and activator of transcription (STAT) 3 is extensively involved in the development, homeostasis, and function of immune cells, with STAT3 disruption associated with human immune-related disorders. The roles ascribed to STAT3 have been assumed to be due to its canonical mode of action as an inducible transcription factor downstream of multiple cytokines, although alternative noncanonical functional modalities have also been identified. The relative involvement of each mode was further explored in relevant zebrafish models.

METHODS

Genome editing with CRISPR/Cas9 was used to generate mutants of the conserved zebrafish Stat3 protein: a loss of function knockout (KO) mutant and a mutant lacking C-terminal sequences including the transactivation domain (ΔTAD). Lines harboring these mutations were analyzed with respect to blood and immune cell development and function in comparison to wild-type zebrafish.

RESULTS

The Stat3 KO mutant showed perturbation of hematopoietic lineages throughout primitive and early definitive hematopoiesis. Neutrophil numbers did not increase in response to lipopolysaccharide (LPS) or granulocyte colony-stimulating factor (G-CSF) and their migration was significantly diminished, the latter correlating with abrogation of the Cxcl8b/Cxcr2 pathway, with macrophage responses perturbed. Intriguingly, many of these phenotypes were not shared by the Stat3 ΔTAD mutant. Indeed, only neutrophil and macrophage development were disrupted in these mutants with responsiveness to LPS and G-CSF maintained, and neutrophil migration actually increased.

CONCLUSION

This study has identified roles for zebrafish Stat3 within hematopoietic stem cells impacting multiple lineages throughout primitive and early definitive hematopoiesis, myeloid cell responses to G-CSF and LPS and neutrophil migration. Many of these roles showed conservation, but notably several involved noncanonical modalities, providing additional insights for relevant diseases.

Stat3 Has a Different Role in Axon Growth During Development Than It Does in Axon Regeneration After Injury

Signal transducer and activator of transcription 3 (STAT3) is essential for neural development and regeneration as a key transcription factor and mitochondrial activator. However, the mechanism of Stat3 in axon development and regeneration has not been fully understood. In this study, using zebrafish posterior lateral line (PLL) axons, we demonstrate that Stat3 plays distinct roles in PLL axon embryonic growth and regeneration. Our experiments indicate that stat3 is required for PLL axon extension. In stat3 mutant zebrafish, the PLL axon ends were stalled at the level of the cloaca, and expression of stat3 rescues the PLL axon growth in a cell-autonomous manner. Jak/Stat signaling inhibition did not affect PLL axon growth indicating Jak/Stat was dispensable for PLL axon growth. In addition, we found that Stat3 was co-localized with mitochondria in PLL axons and important for the mitochondrial membrane potential and ATPase activity. The PLL axon growth defect of stat3 mutants was mimicked and rescued by rotenone and DCHC treatment, respectively, which suggests that Stat3 regulates PLL axon growth through mitochondrial Stat3. By contrast, mutation of stat3 or Jak/Stat signaling inhibition retarded PLL axon regeneration. Meanwhile, we also found Schwann cell migration was also inhibited in stat3 mutants. Taken together, Stat3 is required for embryonic PLL axon growth by regulating the ATP synthesis efficiency of mitochondria, whereas Stat3 stimulates PLL axon regeneration by regulating Schwann cell migration via Jak/Stat signaling. Our findings show a new mechanism of Stat3 in axon growth and regeneration.

Contribution of Signal Transducer and Activator of Transcription 3 (STAT3) to Bone Development and Repair

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor activated canonically by numerous cytokines and other factors, with significant roles in immunity, immune diseases, and cancer. It has also been implicated in several human skeletal disorders, with loss-of-function (LOF) mutations associated with aberrant skeletal development. To gain further insights, two zebrafish STAT3 lines were investigated: a complete LOF knockout (KO) mutant and a partial LOF mutant with the transactivation domain truncated (ΔTAD). Consistent with other studies, the KO mutants were smaller, with reduced length in early embryos exacerbated by a decreased growth rate from 5 days postfertilization (dpf). They displayed skeletal deformities that approached 80% incidence by 30 dpf, with a significant reduction in early bone but not cartilage formation. Further analysis additionally identified considerable abrogation of caudal fin regeneration, concomitant with a paucity of infiltrating macrophages and neutrophils, which may be responsible for this. Most of these phenotypes were also observed in the ΔTAD mutants, indicating that loss of canonical STAT3 signaling was the likely cause. However, the impacts on early bone formation and regeneration were muted in the ΔTAD mutant, suggesting the potential involvement of noncanonical functions in these processes.

Talin-1 inhibits Smurf1-mediated Stat3 degradation to modulate β-cell proliferation and mass in mice

Insufficient pancreatic β-cell mass and reduced insulin expression are key events in the pathogenesis of diabetes mellitus (DM). Here we demonstrate the high expression of Talin-1 in β-cells and that deficiency of Talin-1 reduces β-cell proliferation, which leads to reduced β-cell mass and insulin expression, thus causing glucose intolerance without affecting peripheral insulin sensitivity in mice. High-fat diet fed exerbates these phenotypes. Mechanistically, Talin-1 interacts with the E3 ligase smad ubiquitination regulatory factor 1 (Smurf1), which prohibits ubiquitination of the signal transducer and activator of transcription 3 (Stat3) mediated by Smurf1, and ablation of Talin-1 enhances Smurf1-mediated ubiquitination of Stat3, leading to decreased β-cell proliferation and mass. Furthermore, haploinsufficiency of Talin-1 and Stat3 genes, but not that of either gene, in β-cell in mice significantly impairs glucose tolerance and insulin expression, indicating that both factors indeed function in the same genetic pathway. Finally, inducible deletion Talin-1 in β-cell causes glucose intolerance in adult mice. Collectively, our findings reveal that Talin-1 functions as a crucial regulator of β-cell mass, and highlight its potential as a therapeutic target for DM patients.

Daily Rhythmicity of Muscle-Related and Rhythm Genes Expression in Mackerel Tuna (Euthynnus affinis)

The aim of this study was to investigate the circadian rhythm of muscle-related gene expression in mackerel tuna under different weather conditions. The experiment was carried out under two weather conditions at four sampling times (6:00, 12:00, 18:00, and 24:00) to determine the expression of growth, function, and rhythm genes: white muscle rhythm genes were rhythmic on sunny and cloudy days, except for PER3 and RORA; all functional genes had daily rhythmicity. Red muscle had daily rhythmicity on both sunny and cloudy days; functional genes had daily rhythmicity except for MBNL. The expression levels of the rhythm gene PER1 were determined to be significantly different by independent t-test samples in white muscle at 6:00, 12:00, 18:00, and 24:00 under different weather conditions; the expression levels of the functional genes MBNL and MSTN were both significantly different. In the red muscle, the expression of the rhythm genes PER3, REVERBA, and BMAL1 was determined by independent t-test samples at 6:00, 12:00, 18:00, and 24:00 on cloudy and sunny days; the functional gene MBNL was significantly different. The present study showed that mackerel tuna muscle rhythm genes and functional genes varied significantly in expression levels depending on weather, time of day, and light intensity and that the expression levels of myogenic genes were closely related to clock gene expression. The fish were also able to adapt to changes in light intensity in different weather conditions through positive physiological regulation.

Zmiz1 is a novel regulator of lymphatic endothelial cell gene expression and function

Zinc Finger MIZ-Type Containing 1 (Zmiz1), also known as ZIMP10 or RAI17, is a transcription cofactor and member of the Protein Inhibitor of Activated STAT (PIAS) family of proteins. Zmiz1 is critical for a variety of biological processes including vascular development. However, its role in the lymphatic vasculature is unknown. In this study, we utilized human dermal lymphatic endothelial cells (HDLECs) and an inducible, lymphatic endothelial cell (LEC)-specific Zmiz1 knockout mouse model to investigate the role of Zmiz1 in LECs. Transcriptional profiling of Zmiz1-deficient HDLECs revealed downregulation of genes crucial for lymphatic vessel development. Additionally, our findings demonstrated that loss of Zmiz1 results in reduced expression of proliferation and migration genes in HDLECs and reduced proliferation and migration in vitro. We also presented evidence that Zmiz1 regulates Prox1 expression in vitro and in vivo by modulating chromatin accessibility at Prox1 regulatory regions. Furthermore, we observed that loss of Zmiz1 in mesenteric lymphatic vessels significantly reduced valve density. Collectively, our results highlight a novel role of Zmiz1 in LECs and as a transcriptional regulator of Prox1, shedding light on a previously unknown regulatory factor in lymphatic vascular biology.

STAT3 and HIF1α cooperatively mediate the transcriptional and physiological responses to hypoxia

STAT3 and HIF1α are two fundamental transcription factors involved in many merging processes, like angiogenesis, metabolism, and cell differentiation. Notably, under pathological conditions, the two factors have been shown to interact genetically, but both the molecular mechanisms underlying such interactions and their relevance under physiological conditions remain unclear. In mouse embryonic stem cells (ESCs) we manage to determine the specific subset of hypoxia-induced genes that need STAT3 to be properly transcribed and, among them, fundamental genes like Vegfa, Hk1, Hk2, Pfkp and Hilpda are worth mentioning. Unexpectedly, we also demonstrated that the absence of STAT3 does not affect the expression of Hif1α mRNA nor the stabilization of HIF1α protein, but the STAT3-driven regulation of the hypoxia-dependent subset of gene could rely on the physical interaction between STAT3 and HIF1α. To further elucidate the physiological roles of this STAT3 non-canonical nuclear activity, we used a CRISPR/Cas9 zebrafish stat3 knock-out line. Notably, hypoxia-related fluorescence of the hypoxia zebrafish reporter line (HRE:mCherry) cannot be induced when Stat3 is not active and, while Stat3 Y705 phosphorylation seems to have a pivotal role in this process, S727 does not affect the Stat3-dependent hypoxia response. Hypoxia is fundamental for vascularization, angiogenesis and immune cells mobilization; all processes that, surprisingly, cannot be induced by low oxygen levels when Stat3 is genetically ablated. All in all, here we report the specific STAT3/HIF1α-dependent subset of genes in vitro and, for the first time with an in vivo model, we determined some of the physiological roles of STAT3-hypoxia crosstalk.

Splicing factor deficits render hematopoietic stem and progenitor cells sensitive to STAT3 inhibition

Hematopoietic stem and progenitor cells (HSPCs) sustain lifelong hematopoiesis. Mutations of pre-mRNA splicing machinery, especially splicing factor 3b, subunit 1 (SF3B1), are early lesions found in malignancies arising from HSPC dysfunction. However, why splicing factor deficits contribute to HSPC defects remains incompletely understood. Using zebrafish, we show that HSPC formation in sf3b1 homozygous mutants is dependent on STAT3 activation. Clinically, mutations in SF3B1 are heterozygous; thus, we explored if targeting STAT3 could be a vulnerability in these cells. We show that SF3B1 heterozygosity confers heightened sensitivity to STAT3 inhibition in zebrafish, mouse, and human HSPCs. Cells carrying mutations in other splicing factors or treated with splicing modulators are also more sensitive to STAT3 inhibition. Mechanistically, we illustrate that STAT3 inhibition exacerbates aberrant splicing in SF3B1 mutant cells. Our findings reveal a conserved vulnerability of splicing factor mutant HSPCs that could allow for their selective targeting in hematologic malignancies.

The detection of mutation within goat cell division cycle 25 A and its effect on kidding number

Cell division cycle 25 A (CDC25A) accounts for an essential function on early folliculogenesis of female mammals, especially regulating the function of intra-ovarian, thus this gene is pinpointed as a candidate gene that influences the kidding number of goat. On this ground, the purpose of this study was to investigate whether the reported 20-nt nucleotide variants locus (rs639467625) of the CDC25A gene influences kidding number in Shaanbei white cashmere goat (SBWC). The χ²-test showed that there were more ID genotypes in mothers of multiple lambs than in mothers of single lambs. Interestingly, this indel locus was related to the first-born kidding number in the group of SBWC goats (p < 0.05). Similarly, the result of the t-test was consistent with the result of the χ²-test, showed the kidding number of ID genotype individuals was large than that of II individuals (p < 0.05). These findings proved that the different genotypes of CDC25A have impacts on goat kidding numbers. Thus, the results led us to speculate that the ID genotype of CDC25A was one of the main indel influencing goat kidding numbers. Simultaneously, this study was expected to provide useful DNA markers for superior individuals selection by marker-assisted selection (MAS) and make a contribution to goats breeding.

Variable phenotypes and penetrance between and within different zebrafish ciliary transition zone mutants

Meckel syndrome, nephronophthisis, Joubert syndrome and Bardet-Biedl syndrome are caused by mutations in proteins that localize to the ciliary transition zone (TZ). The phenotypically distinct syndromes suggest that these TZ proteins have differing functions. However, mutations in a single TZ gene can result in multiple syndromes, suggesting that the phenotype is influenced by modifier genes. We performed a comprehensive analysis of ten zebrafish TZ mutants, including mks1, tmem216, tmem67, rpgrip1l, cc2d2a, b9d2, cep290, tctn1, nphp1 and nphp4, as well as mutants in ift88 and ift172. Our data indicate that variations in phenotypes exist between different TZ mutants, supporting different tissue-specific functions of these TZ genes. Further, we observed phenotypic variations within progeny of a single TZ mutant, reminiscent of multiple disease syndromes being associated with mutations in one gene. In some mutants, the dynamics of the phenotype became complex with transitory phenotypes that are corrected over time. We also demonstrated that multiple-guide-derived CRISPR/Cas9 F0 'crispant' embryos recapitulate zygotic null phenotypes, and rapidly identified ciliary phenotypes in 11 cilia-associated gene candidates (ankfn1, ccdc65, cfap57, fhad1, nme7, pacrg, saxo2, c1orf194, ttc26, zmynd12 and cfap52).

Zebrafish: an important model for understanding scoliosis

Scoliosis is a common spinal deformity that considerably affects the physical and psychological health of patients. Studies have shown that genetic factors play an important role in scoliosis. However, its etiopathogenesis remain unclear, partially because of the genetic heterogeneity of scoliosis and the lack of appropriate model systems. Recently, the development of efficient gene editing methods and high-throughput sequencing technology has made it possible to explore the underlying pathological mechanisms of scoliosis. Owing to their susceptibility for developing scoliosis and high genetic homology with human, zebrafish are increasingly being used as a model for scoliosis in developmental biology, genetics, and clinical medicine. Here, we summarize the recent advances in scoliosis research on zebrafish and discuss the prospects of using zebrafish as a scoliosis model.

Functional Analysis of Zebrafish socs4a: Impacts on the Notochord and Sensory Function

The suppressor of cytokine signaling (SOCS) proteins play important roles in cytokine and growth factor signaling, where they act principally as negative feedback regulators, particularly of the downstream signal transducer and activator of transcription (STAT) transcription factors. This critical mode of regulation impacts on both development and homeostasis. However, understanding of the function of SOCS4 remains limited. To address this, we investigated one of the zebrafish SOCS4 paralogues, socs4a, analyzing its expression and the consequences of its ablation. The socs4a gene had a dynamic expression profile during zebrafish embryogenesis, with initial ubiquitous expression becoming restricted to sensory ganglion within the developing nervous system. The knockdown of zebrafish socs4a revealed novel roles in notochord development, as well as the formation of a functional sensory system.

gp130/STAT3 signaling is required for homeostatic proliferation and anabolism in postnatal growth plate and articular chondrocytes

Growth of long bones and vertebrae is maintained postnatally by a long-lasting pool of progenitor cells. Little is known about the molecular mechanisms that regulate the output and maintenance of the cells that give rise to mature cartilage. Here we demonstrate that postnatal chondrocyte-specific deletion of a transcription factor Stat3 results in severely reduced proliferation coupled with increased hypertrophy, growth plate fusion, stunting and signs of progressive dysfunction of the articular cartilage. This effect is dimorphic, with females more strongly affected than males. Chondrocyte-specific deletion of the IL-6 family cytokine receptor gp130, which activates Stat3, phenocopied Stat3-deletion; deletion of Lifr, one of many co-receptors that signals through gp130, resulted in a milder phenotype. These data define a molecular circuit that regulates chondrogenic cell maintenance and output and reveals a pivotal positive function of IL-6 family cytokines in the skeletal system with direct implications for skeletal development and regeneration.

Genetic animal models of scoliosis: A systematical review

Scoliosis is a complex disease with undetermined pathogenesis and has a strong relationship with genetics. Models of scoliosis in animals have been established for better comprehending its pathogenesis and treatment. In this review, we searched all the genetic animal models with body curvature in databases, and reviewed the related genes and scoliosis types. Meanwhile, we also summarized the pathogenesis of scoliosis reported so far. Summarizing the positive phenotypic animal models contributes to a better understanding on the pathogenesis of scoliosis and facilitates the selection of experimental models when a possible pathogenic factor is concerned.

Interleukin-11 signaling promotes cellular reprogramming and limits fibrotic scarring during tissue regeneration

Damage-induced fibrotic scarring limits tissue regeneration in mammals and is a leading cause of morbidity. In contrast, species like zebrafish can regenerate damaged tissues without excessive fibrosis. However, whether specific signaling pathways can both limit fibrosis and promote regeneration is unclear. Here, we show that interleukin-11 (Il-11)/Stat3 signaling has such a dual function. Zebrafish lacking Il-11 receptor function display severely compromised heart, fin, and scale regeneration. Deep phenotyping and transcriptional analysis of adult hearts and fins show that Il-11 signaling drives cellular reprogramming to orchestrate global and tissue-specific regenerative programs and broadly antagonizes hallmarks of adult mammalian scarring. Mechanistically, our data indicate that IL-11 signaling in endothelial cells antagonizes profibrotic transforming growth factor–β signaling and endothelial-to-mesenchymal transition, limiting scarring and promoting cardiomyocyte repopulation, after injury. Overall, our findings position damage-induced Il-11/Stat3 signaling in a key role limiting fibrosis and promoting regeneration, revealing novel targets for regenerative therapies.

Y705 and S727 are required for the mitochondrial import and transcriptional activities of STAT3, and for regulation of stem cell proliferation

The STAT3 transcription factor, acting both in the nucleus and mitochondria, maintains embryonic stem cell pluripotency and promotes their proliferation. In this work, using zebrafish, we determined in vivo that mitochondrial STAT3 regulates mtDNA transcription in embryonic and larval stem cell niches and that this activity affects their proliferation rates. As a result, we demonstrated that import of STAT3 inside mitochondria requires Y705 phosphorylation by Jak, whereas its mitochondrial transcriptional activity, as well as its effect on proliferation, depends on the MAPK target S727. These data were confirmed using mouse embryonic stem cells: although the Y705-mutated STAT3 cannot enter mitochondria, the S727 mutation does not affect import into the organelle and is responsible for STAT3-dependent mitochondrial transcription. Surprisingly, STAT3-dependent increase of mitochondrial transcription appears to be independent from STAT3 binding to STAT3-responsive elements. Finally, loss-of-function experiments, with chemical inhibition of the JAK/STAT3 pathway or genetic ablation of stat3 gene, demonstrated that STAT3 is also required for cell proliferation in the intestine of zebrafish.

Summary: Mitochondrial import of STAT3 requires Y705 phosphorylation by Jak, whereas STAT3 mitochondrial transcriptional activity and its effect on proliferation depend on the MAPK target S727.

Applying Bioinformatic Platforms, In Vitro, and In Vivo Functional Assays in the Characterization of Genetic Variants in the GH/IGF Pathway Affecting Growth and Development

Heritability accounts for over 80% of adult human height, indicating that genetic variability is the main determinant of stature. The rapid technological development of Next-Generation Sequencing (NGS), particularly Whole Exome Sequencing (WES), has resulted in the characterization of several genetic conditions affecting growth and development. The greatest challenge of NGS remains the high number of candidate variants identified. In silico bioinformatic tools represent the first approach for classifying these variants. However, solving the complicated problem of variant interpretation requires the use of experimental approaches such as in vitro and, when needed, in vivo functional assays. In this review, we will discuss a rational approach to apply to the gene variants identified in children with growth and developmental defects including: (i) bioinformatic tools; (ii) in silico modeling tools; (iii) in vitro functional assays; and (iv) the development of in vivo models. While bioinformatic tools are useful for a preliminary selection of potentially pathogenic variants, in vitro—and sometimes also in vivo—functional assays are further required to unequivocally determine the pathogenicity of a novel genetic variant. This long, time-consuming, and expensive process is the only scientifically proven method to determine causality between a genetic variant and a human genetic disease.

Preclinical models of diabetic wound healing: A critical review

The treatment of diabetic wounds (DWs) is always challenging for the medical community because of its multifaceted pathophysiology. Due to practical and ethical considerations, direct studies of therapeutic interventions on human subjects are limited. Thus, it is ideal for performing studies on animals having less genetic and biological variability. An ideal DW model should progress toward reproducibility, quantifiable interpretation, therapeutic significance, and effective translation into clinical use. In the last couple of decades, various animal models were developed to examine the complex cellular and biochemical process of skin restoration in DW healing. Also, these models were used to assess the potency of developed active pharmaceutical ingredients and formulations. However, many animal models lack studying mechanisms that can appropriately restate human DW, stay a huge translational challenge. This review discusses the available animal models with their significance in DW experiments and their limitations, focusing on levels of proof of effectiveness in selecting appropriate models to restate the human DW to improve clinical outcomes. Although numerous newer entities and combinatory formulations are very well appreciated preclinically for DW management, they fail in clinical trials, which may be due to improper selection of the appropriate model. The major future challenge could be developing a model that resembles the human DW environment, can potentiate translational research in DW care.

Stat3 loss in mesenchymal progenitors causes Job syndrome-like skeletal defects by reducing Wnt/β-catenin signaling

Job syndrome is a rare genetic disorder caused by STAT3 mutations and primarily characterized by immune dysfunction along with comorbid skeleton developmental abnormalities including osteopenia, recurrent fracture of long bones, and scoliosis. So far, there is no definitive cure for the skeletal defects in Job syndrome, and treatments are limited to management of clinical symptoms only. Here, we have investigated the molecular mechanism whereby Stat3 regulates skeletal development and osteoblast differentiation. We showed that removing Stat3 function in the developing limb mesenchyme or osteoprogenitor cells in mice resulted in shortened and bow limbs with multiple fractures in long bones that resembled the skeleton symptoms in the Job Syndrome. However, Stat3 loss did not alter chondrocyte differentiation and hypertrophy in embryonic development, while osteoblast differentiation was severely reduced. Genome-wide transcriptome analyses as well as biochemical and histological studies showed that Stat3 loss resulted in down-regulation of Wnt/β-catenin signaling. Restoration of Wnt/β-catenin signaling by injecting BIO, a small molecule inhibitor of GSK3, or crossing with a Lrp5 gain of function (GOF) allele, rescued the bone reduction phenotypes due to Stat3 loss to a great extent. These studies uncover the essential functions of Stat3 in maintaining Wnt/β-catenin signaling in early mesenchymal or osteoprogenitor cells and provide evidence that bone defects in the Job Syndrome are likely caused by Wnt/β-catenin signaling reduction due to reduced STAT3 activities in bone development. Enhancing Wnt/β-catenin signaling could be a therapeutic approach to reduce bone symptoms of Job syndrome patients.

Grass carp (Ctenopharyngodon idellus) Cdc25a down-regulates IFN 1 expression by reducing TBK1 phosphorylation

In vertebrates, TANK Binding Kinase 1 (TBK1) plays an important role in innate immunity, mainly because it can mediate production of interferon to resist the invasion of pathogens. In mammals, cell division cycle-25a (Cdc25a) is a member of the Cdc25 family of cell division cycle proteins. It is a phosphatase that plays an important role in cell cycle regulation by dephosphorylating its substrate proteins. Currently, many phosphatases are reported to play a role in innate immunity. This is because the phosphatases can shut down or reduce immune signaling pathways by down-regulating phosphorylation signals. However, there are no reports on fish Cdc25a in innate immunity. In this paper, we conducted a preliminary study on the involvement of grass carp Cdc25a in innate immunity. First, we cloned the full-length cDNA of grass carp Cdc25a (CiCdc25a), and found that it shares the highest genetic relationship with that of Anabarilius grahami through phylogenetic tree comparison. In grass carp tissues and CIK cells, the expression of CiCdc25a mRNA was up-regulated under poly (I:C) stimulation. Therefore, CiCdc25a can respond to poly (I:C). The subcellular localization results showed that CiCdc25a is distributed both in the cytoplasm and nucleus. We also found that CiCdc25a can down-regulate the expression of IFN 1 with or without poly (I:C) stimulation. In other words, the down-regulation of IFN1 by CiCdc25a is independent of poly (I:C) stimulation. Further functional studies have shown that the inhibition of IFN1 expression by CiCdc25a may be related to decrease of TBK1 activity. We also confirmed that the phosphorylation of TBK1 at Ser172 is essential for production of IFN 1. In short, CiCdc25a can interact with TBK1 and subsequently inhibits the phosphorylation of TBK1, thereby weakens TBK1 activity. These results indicated that grass carp Cdc25a down-regulates IFN 1 expression by reducing TBK1 phosphorylation.

Postembryonic screen for mutations affecting spine development in zebrafish

The spine gives structural support for the adult body, protects the spinal cord, and provides muscle attachment for moving through the environment. The development and maturation of the spine and its physiology involve the integration of multiple musculoskeletal tissues including bone, cartilage, and fibrocartilaginous joints, as well as innervation and control by the nervous system. One of the most common disorders of the spine in human is adolescent idiopathic scoliosis (AIS), which is characterized by the onset of an abnormal lateral curvature of the spine of <10° around adolescence, in otherwise healthy children. The genetic basis of AIS is largely unknown. Systematic genome-wide mutagenesis screens for embryonic phenotypes in zebrafish have been instrumental in the understanding of early patterning of embryonic tissues necessary to build and pattern the embryonic spine. However, the mechanisms required for postembryonic maturation and homeostasis of the spine remain poorly understood. Here we report the results from a small-scale forward genetic screen for adult-viable recessive and dominant zebrafish mutations, leading to overt morphological abnormalities of the adult spine. Germline mutations induced with N-ethyl N-nitrosourea (ENU) were transmitted and screened for dominant phenotypes in 1229 F1 animals, and subsequently bred to homozygosity in F3 families; from these, 314 haploid genomes were screened for adult-viable recessive phenotypes affecting general body shape. We cumulatively found 40 adult-viable (3 dominant and 37 recessive) mutations each leading to a defect in the morphogenesis of the spine. The largest phenotypic group displayed larval onset axial curvatures, leading to whole-body scoliosis without vertebral dysplasia in adult fish. Pairwise complementation testing of 16 mutant lines within this phenotypic group revealed at least 9 independent mutant loci. Using massively-parallel whole genome or whole exome sequencing and meiotic mapping we defined the molecular identity of several loci for larval onset whole-body scoliosis in zebrafish. We identified a new mutation in the skolios/kinesin family member 6 (kif6) gene, causing neurodevelopmental and ependymal cilia defects in mouse and zebrafish. We also report multiple recessive alleles of the scospondin and a disintegrin and metalloproteinase with thrombospondin motifs 9 (adamts9) genes, which all display defects in spine morphogenesis. Our results provide evidence of monogenic traits that are essential for normal spine development in zebrafish, that may help to establish new candidate risk loci for spine disorders in humans.

Thermal Proteome Profiling in Zebrafish Reveals Effects of Napabucasin on Retinoic Acid Metabolism

Thermal proteome profiling (TPP) allows for the unbiased detection of drug-target protein engagements in vivo. Traditionally, 1 cell type is used for TPP studies, with the risk of missing important differentially expressed target proteins. The use of whole organisms would circumvent this problem. Zebrafish embryos are amenable to such an approach. Here, we used TPP on whole zebrafish embryo lysate to identify protein targets of napabucasin, a compound that may affect signal transducer and activator of transcription 3 (Stat3) signaling through an ill-understood mechanism. In zebrafish embryos, napabucasin induced developmental defects consistent with inhibition of Stat3 signaling. TPP profiling showed no distinct shift in Stat3 upon napabucasin treatment, but effects were detected on the oxidoreductase, Pora, which might explain effects on Stat3 signaling. Interestingly, thermal stability of several aldehyde dehydrogenases was affected. Moreover, napabucasin activated aldehyde dehydrogenase enzymatic activity in vitro. Aldehyde dehydrogenases have crucial roles in retinoic acid metabolism, and functionally, we validated napabucasin-mediated activation of the retinoic acid pathway in zebrafish in vivo. We conclude that TPP profiling in whole zebrafish embryo lysate is feasible and facilitates direct correlation of in vivo effects of small molecule drugs with their protein targets.

Teratogenic, Oxidative Stress and Behavioural Outcomes of Three Fungicides of Natural Origin (Equisetum arvense, Mimosa tenuiflora, Thymol) on Zebrafish (Danio rerio)

The improper use of synthetic fungicides has raised public concerns related to environmental pollution and animal health. Over the years, plant-derived antifungals have been investigated as safer alternatives, although little scientific evidence of its neurodevelopmental effects exist. The main objective of this study was to explore the effects of three alternative natural extracts (Equisetum arvense, Mimosa tenuiflora, Thymol) with antifungal properties during the early development of zebrafish by evaluating different teratogenic, oxidative stress and behavioural outcomes. Following the determination of the 96 h-LC₅₀, exposure to sublethal concentrations showed the safety profile of both E. arvense and M. tenuiflora. However, following 96-h exposure to Thymol, increased lethality, pericardial oedema, yolk and eye deformations, and decreased body length were observed. The reduced and oxidized glutathione (GSH:GSSG) ratio was increased, and the glutathione-s-transferase activity in the group exposed to the highest Thymol concentration. Overall, these results support a more reducing environment associated with possible effects at the cellular proliferation level. In addition, the disruption of behavioural states (fear- and anxiety-like disorders) were noted, pointing to alterations in the c-Jun N-terminal kinase developmental signalling pathway, although further studies are required to explore this rationale. Notwithstanding, the results provide direct evidence of the teratogenic effects of Thymol, which might have consequences for non-target species.

The stem-like Stat3-responsive cells of zebrafish intestine are Wnt/β-catenin dependent

The transcription factor Stat3 is required for proliferation and pluripotency of embryonic stem cells; we have prepared and characterized fluorescent Stat3-reporter zebrafish based on repeats of minimal responsive elements. These transgenic lines mimic in vivo Stat3 expression patterns and are responsive to exogenous Stat3; notably, fluorescence is inhibited by both stat3 knockout and IL6/Jak/STAT inhibitors. At larval stages, Stat3 reporter activity correlates with proliferating regions of the brain, haematopoietic tissue and intestine. In the adult gut, the reporter is active in sparse proliferating cells, located at the base of intestinal folds, expressing the stemness marker sox9b and having the morphology of mammalian crypt base columnar cells; noteworthy, zebrafish stat3 mutants show defects in intestinal folding. Stat3 reporter activity in the gut is abolished with mutation of T cell factor 4 (Tcf7l2), the intestinal mediator of Wnt/β-catenin-dependent transcription. The Wnt/β-catenin dependence of Stat3 activity in the gut is confirmed by abrupt expansion of Stat3-positive cells in intestinal adenomas of apc heterozygotes. Our findings indicate that Jak/Stat3 signalling is needed for intestinal stem cell maintenance and possibly crucial in controlling Wnt/β-catenin-dependent colorectal cancer cell proliferation.

Summary: Using a fluorescent reporter for Stat3 activity, we have identified the stem cells of zebrafish intestine and characterized their Wnt requirements and responsiveness.

Maternal contributions to gastrulation in zebrafish

Gastrulation is a critical early morphogenetic process of animal development, during which the three germ layers; mesoderm, endoderm and ectoderm, are rearranged by internalization movements. Concurrent epiboly movements spread and thin the germ layers while convergence and extension movements shape them into an anteroposteriorly elongated body with head, trunk, tail and organ rudiments. In zebrafish, gastrulation follows the proliferative and inductive events that establish the embryonic and extraembryonic tissues and the embryonic axis. Specification of these tissues and embryonic axes are controlled by the maternal gene products deposited in the egg. These early maternally controlled processes need to generate sufficient cell numbers and establish the embryonic polarity to ensure normal gastrulation. Subsequently, after activation of the zygotic genome, the zygotic gene products govern mesoderm and endoderm induction and germ layer patterning. Gastrulation is initiated during the maternal-to-zygotic transition, a process that entails both activation of the zygotic genome and downregulation of the maternal transcripts. Genomic studies indicate that gastrulation is largely controlled by the zygotic genome. Nonetheless, genetic studies that investigate the relative contributions of maternal and zygotic gene function by comparing zygotic, maternal and maternal zygotic mutant phenotypes, reveal significant contribution of maternal gene products, transcripts and/or proteins, that persist through gastrulation, to the control of gastrulation movements. Therefore, in zebrafish, the maternally expressed gene products not only set the stage for, but they also actively participate in gastrulation morphogenesis.

Nodal and planar cell polarity signaling cooperate to regulate zebrafish convergence and extension gastrulation movements

During vertebrate gastrulation, convergence and extension (C and E) of the primary anteroposterior (AP) embryonic axis is driven by polarized mediolateral (ML) cell intercalations and is influenced by AP axial patterning. Nodal signaling is essential for patterning of the AP axis while planar cell polarity (PCP) signaling polarizes cells with respect to this axis, but how these two signaling systems interact during C and E is unclear. We find that the neuroectoderm of Nodal-deficient zebrafish gastrulae exhibits reduced C and E cell behaviors, which require Nodal signaling in both cell- and non-autonomous fashions. PCP signaling is partially active in Nodal-deficient embryos and its inhibition exacerbates their C and E defects. Within otherwise naïve zebrafish blastoderm explants, however, Nodal induces C and E in a largely PCP-dependent manner, arguing that Nodal acts both upstream of and in parallel with PCP during gastrulation to regulate embryonic axis extension cooperatively.

Zebrafish embryonic explants undergo genetically encoded self-assembly

Embryonic stem cell cultures are thought to self-organize into embryoid bodies, able to undergo symmetry-breaking, germ layer specification and even morphogenesis. Yet, it is unclear how to reconcile this remarkable self-organization capacity with classical experiments demonstrating key roles for extrinsic biases by maternal factors and/or extraembryonic tissues in embryogenesis. Here, we show that zebrafish embryonic tissue explants, prepared prior to germ layer induction and lacking extraembryonic tissues, can specify all germ layers and form a seemingly complete mesendoderm anlage. Importantly, explant organization requires polarized inheritance of maternal factors from dorsal-marginal regions of the blastoderm. Moreover, induction of endoderm and head-mesoderm, which require peak Nodal-signaling levels, is highly variable in explants, reminiscent of embryos with reduced Nodal signals from the extraembryonic tissues. Together, these data suggest that zebrafish explants do not undergo bona fide self-organization, but rather display features of genetically encoded self-assembly, where intrinsic genetic programs control the emergence of order.

Notochord vacuoles absorb compressive bone growth during zebrafish spine formation

The vertebral column or spine assembles around the notochord rod which contains a core made of large vacuolated cells. Each vacuolated cell possesses a single fluid-filled vacuole, and loss or fragmentation of these vacuoles in zebrafish leads to spine kinking. Here, we identified a mutation in the kinase gene dstyk that causes fragmentation of notochord vacuoles and a severe congenital scoliosis-like phenotype in zebrafish. Live imaging revealed that Dstyk regulates fusion of membranes with the vacuole. We find that localized disruption of notochord vacuoles causes vertebral malformation and curving of the spine axis at those sites. Accordingly, in dstyk mutants the spine curves increasingly over time as vertebral bone formation compresses the notochord asymmetrically, causing vertebral malformations and kinking of the axis. Together, our data show that notochord vacuoles function as a hydrostatic scaffold that guides symmetrical growth of vertebrae and spine formation.

Overexpressed circPVT1 in oral squamous cell carcinoma promotes proliferation by serving as a miRNA sponge

Circular RNAs (circRNAs) comprise a novel class of widespread non‑coding RNAs that may regulate gene expression in eukaryotes. However, the characterization and function of circRNAs remain elusive in human cancer, including oral squamous cell carcinoma (OSCC). In this study, the expression level of circPVT1 in OSCC was detected and define its functional role in initiation and progression of OSCC. It was identified that circPVT1 was upregulated in OSCC cells and specimens. Knockdown of circPVT1 suppressed cell proliferation as evidenced by Cell Counting kit‑8 assay and elevated Ki‑67 expression. Mechanistically, it was demonstrated that circPVT1 possessed two targeting sites of microRNA (miRNA/miR)‑125b and could effectively sponge miR‑125b to release its downstream mRNA targets. Subsequently, the downstream target signal transducer and activator of transcription 3 (STAT3) was verified as a direct target of miR‑125b and STAT3 expression was regulated by the circPVT1/miR‑125b axis. CircPVT1 functioned as competing endogenous RNA (ceRNA) to increase the STAT3 level and cell proliferation through sponging miR‑125b. In conclusion, circPVT1 regulates cell proliferation and may serve as a promising therapeutic target for OSCC patients. Therefore, silencing of circPVT1 could be a future direction to develop a novel treatment strategy.

Shmt2: A Stat3 Signaling New Player in Prostate Cancer Energy Metabolism

Prostate cancer (PCa) is a multifactorial disease characterized by the aberrant activity of different regulatory pathways. STAT3 protein mediates some of these pathways and its activation is implicated in the modulation of several metabolic enzymes. A bioinformatic analysis indicated a STAT3 binding site in the upstream region of SHMT2 gene. We demonstrated that in LNCaP, PCa cells’ SHMT2 expression is upregulated by the JAK2/STAT3 canonical pathway upon IL-6 stimulation. Activation of SHTM2 leads to a decrease in serine levels, pushing PKM2 towards the nuclear compartment where it can activate STAT3 in a non-canonical fashion that in turn promotes a transient shift toward anaerobic metabolism. These results were also confirmed on FFPE prostate tissue sections at different Gleason scores. STAT3/SHMT2/PKM2 loop in LNCaP cells can modulate a metabolic shift in response to inflammation at early stages of cancer progression, whereas a non-canonical STAT3 activation involving the STAT3/HIF-1α/PKM2 loop is responsible for the maintenance of Warburg effect distinctive of more aggressive PCa cells. Chronic inflammation might thus prime the transition of PCa cells towards more advanced stages, and SHMT2 could represent a missing factor to further understand the molecular mechanisms responsible for the transition of prostate cancer towards a more aggressive phenotype.

Distinct inflammatory and wound healing responses to complex caudal fin injuries of larval zebrafish

Wound repair is controlled temporally and spatially to restore tissue homeostasis. Previously we reported that thermal damage of the larval zebrafish fin disrupts collagen organization and wound healing compared to tail transection (LeBert et al., 2018). Here we characterize different injury models in larval zebrafish to dissect temporal and spatial dynamics of repair in complex damage. We found that each damage model triggers distinct inflammatory and tissue responses, with Stat3 and TGFβ playing key roles in the regulation of mesenchymal cells during simple repair. While thermal injury disrupts collagen fibers initially, healing is recovered as inflammation resolves, and mesenchymal cells and collagen fibers align. By contrast, infected wounds lead to persistent inflammation and loss of mesenchymal cells, resulting in minimal tissue repair. These wound models have broad physiological relevance, thereby providing a valuable advance in our toolkit to probe the dynamics of inflammation and wound repair in complex tissue damage.

A 20-bp insertion/deletion (indel) polymorphism within the CDC25A gene and its associations with growth traits in goat

Cell division cycle 25A (CDC25A), a member of the CDC25 family of phosphatases, is required for progression from G1 to the S phase of the cell cycle. CDC25A provides an essential function during early embryonic development in mice, suggesting that it plays an important role in growth and development. In this study, we used mathematical expectation (ME) methods to identify a 20-bp insertion/deletion (indel) polymorphism of CDC25A gene in Shaanbei White Cashmere (SBWC) goats. We also investigated the association between this 20-bp indel and growth-related traits in SBWC goats. Association results showed that the indel was related to growth traits (height at hip cross, cannon circumference, and cannon circumference index) in SBWC goats. The height at hip cross of individuals with insertion/insertion (II) genotype was higher than those with insertion/deletion (ID) genotype (P=0.02); on the contrary, the cannon circumference and cannon circumference index of individuals with ID genotype were superior when compared with those with II genotype (P=0.017 and P=0.009). These findings suggest that the 20-bp indel in the CDC25A gene significantly affects growth-related traits, and could be utilized as a candidate marker for marker-assisted selection (MAS) in the cashmere goat industry.

Induction of interferon-stimulated genes and cellular stress pathways by morpholinos in zebrafish

The phenotypes caused by morpholino-mediated interference of gene function in zebrafish are often not observed in the corresponding mutant(s). We took advantage of the availability of a relatively large collection of transcriptomic datasets to identify common signatures that characterize morpholino-injected animals (morphants). In addition to the previously reported activation of tp53 expression, we observed increased expression of the interferon-stimulated genes (ISGs), isg15 and isg20, the cell death pathway gene casp8, and other cellular stress response genes including phlda3, mdm2 and gadd45aa. Studies involving segmentation stage embryos were more likely to show upregulation of these genes. We also found that the expression of these genes could be upregulated by increasing doses of an egfl7 morpholino, or even high doses of the standard control morpholino. Thus, these data show that morpholinos can induce the expression of ISGs in zebrafish embryos and further our understanding of morpholino effects.

Loss-of-function approaches in comparative physiology: is there a future for knockdown experiments in the era of genome editing?

Loss-of-function technologies, such as morpholino- and RNAi-mediated gene knockdown, and TALEN- and CRISPR/Cas9-mediated gene knockout, are widely used to investigate gene function and its physiological significance. Here, we provide a general overview of the various knockdown and knockout technologies commonly used in comparative physiology and discuss the merits and drawbacks of these technologies with a particular focus on research conducted in zebrafish. Despite their widespread use, there is an ongoing debate surrounding the use of knockdown versus knockout approaches and their potential off-target effects. This debate is primarily fueled by the observations that, in some studies, knockout mutants exhibit phenotypes different from those observed in response to knockdown using morpholinos or RNAi. We discuss the current debate and focus on the discrepancies between knockdown and knockout phenotypes, providing literature and primary data to show that the different phenotypes are not necessarily a direct result of the off-target effects of the knockdown agents used. Nevertheless, given the recent evidence of some knockdown phenotypes being recapitulated in knockout mutants lacking the morpholino or RNAi target, we stress that results of knockdown experiments need to be interpreted with caution. We ultimately argue that knockdown experiments should not be discontinued if proper control experiments are performed, and that with careful interpretation, knockdown approaches remain useful to complement the limitations of knockout studies (e.g. lethality of knockout and compensatory responses).

Lack of Cyclin B1 in zebrafish causes lengthening of G2 and M phases

An essential part of the Mitosis Promoting Factor, Cyclin B1 is indispensable for cells to enter mitosis. We report here that the zebrafish early arrest mutant specter is a loss-of-function mutation in the сyclin B1 gene. cyclin B1 is maternally transcribed in zebrafish, and the zygotic phenotype is apparent by early segmentation. Lack of zygotic Cyclin B1 does not stop cells from dividing, rather it causes an abnormal and elongated progression through the G2 and M phases of the cell cycle. Many mutant cells show signs of chromosomal instability or enter apoptosis. Using CRISPR-mediated gene editing, we produced a more severe gain-of-function mutation confirming that specter is the result of nonfunctional Cyclin B1. Although also a recessive phenotype, this new mutation produces an alternative splice-form of cyclin B1 mRNA, whose product lacks several key components for Cyclin B1, but not the Cdk1-binding domain. This mutant form of Cyclin B1 completely prevents cell division. We conclude that, although Cyclin B1 is critical for cells to enter mitosis, another cell cycle protein may be cooperating with Cdk1 at the G2/M checkpoint to sustain a partly functional Mitosis Promoting Factor.

Stat3 Regulates Liver Progenitor Cell-Driven Liver Regeneration in Zebrafish

After liver injury, regeneration manifests as either (1) hepatocytes proliferating to restore the lost hepatocyte mass or (2) if hepatocyte proliferation is compromised, biliary epithelial cells (BECs) dedifferentiating into liver progenitor cells (LPCs), which subsequently differentiate into hepatocytes. Following pharmacogenetic ablation of hepatocytes in Tg(fabp10a:CFP-NTR) zebrafish, resulting in severe liver injury, signal transducer and activator of transcription 3 (Stat3) and its target gene and negative regulator, socs3a, were upregulated in regenerating livers. Using either Stat3 inhibitors, JSI-124 and S3I-201, or stat3 zebrafish mutants, we investigated the role of Stat3 in LPC-driven liver regeneration. Although Stat3 suppression reduced the size of regenerating livers, BEC dedifferentiation into LPCs was unaffected. However, regenerating livers displayed a delay in LPC-to-hepatocyte differentiation and a significant reduction in the number of BECs. While no difference in cell death was detected, Stat3 inhibition significantly reduced LPC proliferation. Notably, stat3 mutants phenocopied the effects of Stat3 chemical inhibitors, although the mutant phenotype was incompletely penetrant. Intriguingly, a subset of socs3a mutants also displayed a lower number of BECs in regenerating livers. We conclude that the Stat3/Socs3a pathway is necessary for the proper timing of LPC-to-hepatocyte differentiation and establishing the proper number of BECs during LPC-driven liver regeneration.

Gon4l regulates notochord boundary formation and cell polarity underlying axis extension by repressing adhesion genes

Anteroposterior (AP) axis extension during gastrulation requires embryonic patterning and morphogenesis to be spatiotemporally coordinated, but the underlying genetic mechanisms remain poorly understood. Here we define a role for the conserved chromatin factor Gon4l, encoded by ugly duckling (udu), in coordinating tissue patterning and axis extension during zebrafish gastrulation through direct positive and negative regulation of gene expression. Although identified as a recessive enhancer of impaired axis extension in planar cell polarity (PCP) mutants, udu functions in a genetically independent, partially overlapping fashion with PCP signaling to regulate mediolateral cell polarity underlying axis extension in part by promoting notochord boundary formation. Gon4l limits expression of the cell–cell and cell–matrix adhesion molecules EpCAM and Integrinα3b, excesses of which perturb the notochord boundary via tension-dependent and -independent mechanisms, respectively. By promoting formation of this AP-aligned boundary and associated cell polarity, Gon4l cooperates with PCP signaling to coordinate morphogenesis along the AP embryonic axis.

Anteroposterior axis extension during gastrulation is dynamically coordinated, but how this is regulated at a molecular level is unclear. Here, the authors show in zebrafish that the chromatin factor Gon4l, encoded by ugly duckling, coordinates axis extension by modulating EpCAM and Integrinα3b expression.

Germline mutations affecting the histone H4 core cause a developmental syndrome by altering DNA damage response and cell cycle control

Covalent modifications of histones have an established role as chromatin effectors, as they control processes such as DNA replication and transcription, and repair or regulate nucleosomal structure. Loss of modifications on histone N tails, whether due to mutations in genes belonging to histone-modifying complexes or mutations directly affecting the histone tails, causes developmental disorders or has a role in tumorigenesis. More recently, modifications affecting the globular histone core have been uncovered as being crucial for DNA repair, pluripotency and oncogenesis. Here we report monoallelic missense mutations affecting lysine 91 in the histone H4 core (H4K91) in three individuals with a syndrome of growth delay, microcephaly and intellectual disability. Expression of the histone H4 mutants in zebrafish embryos recapitulates the developmental anomalies seen in the patients. We show that the histone H4 alterations cause genomic instability, resulting in increased apoptosis and cell cycle progression anomalies during early development. Mechanistically, our findings indicate an important role for the ubiquitination of H4K91 in genomic stability during embryonic development.