Cooperation of Mtmr8 with PI3K regulates actin filament modeling and muscle development in zebrafish

Embryonic temperature has long-term effects on muscle circRNA expression and somatic growth in Nile tilapia

Embryonic temperature has a lasting impact on muscle phenotype in vertebrates, involving complex molecular mechanisms that encompass both protein-coding and non-coding genes. Circular RNAs (circRNAs) are a class of regulatory RNAs that play important roles in various biological processes, but the effect of variable thermal conditions on the circRNA transcriptome and its long-term impact on muscle growth plasticity remains largely unexplored. To fill this knowledge gap, we performed a transcriptomic analysis of circRNAs in fast muscle of Nile tilapia (Oreochromis niloticus) subjected to different embryonic temperatures (24°C, 28°C and 32°C) and then reared at a common temperature (28°C) for 4 months. Nile tilapia embryos exhibited faster development and subsequently higher long-term growth at 32°C compared to those reared at 28°C and 24°C. Next-generation sequencing data revealed a total of 5,141 unique circRNAs across all temperature groups, of which 1,604, 1,531, and 1,169 circRNAs were exclusively found in the 24°C, 28°C and 32°C groups, respectively. Among them, circNexn exhibited a 1.7-fold (log2) upregulation in the 24°C group and a 1.3-fold (log2) upregulation in the 32°C group when compared to the 28°C group. Conversely, circTTN and circTTN_b were downregulated in the 24°C groups compared to their 28°C and 32°C counterparts. Furthermore, these differentially expressed circRNAs were found to have multiple interactions with myomiRs, highlighting their potential as promising candidates for further investigation in the context of muscle growth plasticity. Taken together, our findings provide new insights into the molecular mechanisms that may underlie muscle growth plasticity in response to thermal variation in fish, with important implications in the context of climate change, fisheries and aquaculture.

Interplay between myotubularins and Ca2+ homeostasis

The myotubularin family, encompassing myotubularin 1 (MTM1) and 14 myotubularin-related proteins (MTMRs), represents a conserved group of phosphatases featuring a protein tyrosine phosphatase domain. Nine members are characterized by an active phosphatase domain C(X)5R, dephosphorylating the D3 position of PtdIns(3)P and PtdIns(3,5)P2. Mutations in myotubularin genes result in human myopathies, and several neuropathies including X-linked myotubular myopathy and Charcot-Marie-Tooth type 4B. MTM1, MTMR6 and MTMR14 also contribute to Ca2+ signaling and Ca2+ homeostasis that play a key role in many MTM-dependent myopathies and neuropathies. Here we explore the evolving roles of MTM1/MTMRs, unveiling their influence on critical aspects of Ca2+ signaling pathways.

Stage-dependent localization of F-actin and Na+ /K+ -ATPase in zebrafish embryos detected using optimized cryosectioning immunostaining protocol

The increasing use of the zebrafish model in biomedical and (eco)toxicological studies aimed at understanding the function of various proteins highlight the importance of optimizing existing methods to study gene and protein expression and localization in this model. In this context, zebrafish cryosections are still underutilized compared with whole-mount preparations. In this study, we used zebrafish embryos (24-120 hpf) to determine key factors for the preparation of high-quality zebrafish cryosections and to determine the optimal protocol for (immuno)fluorescence analyses of Na⁺ /K⁺ -ATPase and F-actin, across developmental stages from 1 to 5 dpf. The results showed that the highest quality zebrafish cryosections were obtained after the samples were fixed in 4% paraformaldehyde (PFA) for 1 h, incubated in 2.5% bovine gelatin/25% sucrose mixture, embedded in OCT, and then sectioned to 8 μm thickness at -20°C. Fluorescence microscopy analysis of phalloidin-labeled zebrafish skeletal muscle revealed that 1-h-4% PFA-fixed samples allowed optimal binding of phalloidin to F-actin. Further immunofluorescence analyses revealed detailed localization of F-actin and Na⁺ /K⁺ -ATPase in various tissues of the zebrafish and a stage-dependent increase in their respective expression in the somitic muscles and pronephros. Finally, staining of zebrafish cryosections and whole-mount samples revealed organ-specific and zone-dependent localizations of the Na⁺ /K⁺ -ATPase α1-subunit. RESEARCH HIGHLIGHTS: This study brings optimization of existing protocols for preparation and use of zebrafish embryos cryosections in (immuno)histological analyses. It reveals stage-dependent localization/expression of F-actin and Na⁺ /K⁺ -ATPase in zebrafish embryos.

miR-100-5p Promotes Epidermal Stem Cell Proliferation through Targeting MTMR3 to Activate PIP3/AKT and ERK Signaling Pathways

Skin epidermal stem cells (EpSCs) play a critical role in wound healing and are ideal seed cells for skin tissue engineering. Exosomes from human adipose-derived stem cells (ADSC-Exos) promote human EpSC proliferation, but the underlying mechanism remains unclear. Here, we investigated the effect of miR-100-5p, one of the most abundant miRNAs in ADSC-Exos, on the proliferation of human EpSCs and explored the mechanisms involved. MTT and BrdU incorporation assays showed that miR-100-5p mimic transfection promoted EpSC proliferation in a time-dependent manner. Cell cycle analysis showed that miR-100-5p mimic transfection significantly decreased the percentage of cells in the G1 phase and increased the percentage of cells in the G2/M phase. Myotubularin-related protein 3 (MTMR3), a lipid phosphatase, was identified as a direct target of miR-100-5p. Knockdown of MTMR3 in EpSCs by RNA interference significantly enhanced cell proliferation, decreased the percentage of cells in the G1 phase and increased the percentage of cells in the S phase. Overexpression of MTMR3 reversed the proproliferative effect of miR-100-5p on EpSCs, indicating that miR-100-5p promoted EpSC proliferation by downregulating MTMR3. Mechanistic studies showed that transfection of EpSCs with miR-100-5p mimics elevated the intracellular PIP3 level, induced AKT and ERK phosphorylation, and upregulated cyclin D1, E1, and A2 expression, which could be attenuated by MTMR3 overexpression. Consistently, intradermal injection of ADSC-Exos or miR-100-5p-enriched ADSC-Exos into cultured human skin tissues significantly reduced MTMR3 expression and increased the thickness of the epidermis and the number of EpSCs in the basal layer of the epidermis. The aforementioned effect of miR-100-5p-enriched ADSC-Exos was stronger than that of ADSC-Exos and was reversed by MTMR3 overexpression. Collectively, our findings indicate that miR-100-5p promotes EpSC proliferation through MTMR3-mediated elevation of PIP3 and activation of AKT and ERK. miR-100-5p-enriched ADSC-Exos can be used to treat skin wound and expand EpSCs for generating epidermal autografts and engineered skin equivalents.

Hereditary Spastic Paraplegia: An Update

Hereditary spastic paraplegia (HSP) is a rare neurodegenerative disorder with the predominant clinical manifestation of spasticity in the lower extremities. HSP is categorised based on inheritance, the phenotypic characters, and the mode of molecular pathophysiology, with frequent degeneration in the axon of cervical and thoracic spinal cord’s lateral region, comprising the corticospinal routes. The prevalence ranges from 0.1 to 9.6 subjects per 100,000 reported around the globe. Though modern medical interventions help recognize and manage the disorder, the symptomatic measures remain below satisfaction. The present review assimilates the available data on HSP and lists down the chromosomes involved in its pathophysiology and the mutations observed in the respective genes on the chromosomes. It also sheds light on the treatment available along with the oral/intrathecal medications, physical therapies, and surgical interventions. Finally, we have discussed the related diagnostic techniques as well as the linked pharmacogenomics studies under future perspectives.

A conserved myotubularin-related phosphatase regulates autophagy by maintaining autophagic flux

Macroautophagy (autophagy) targets cytoplasmic cargoes to the lysosome for degradation. Like all vesicle trafficking, autophagy relies on phosphoinositide identity, concentration, and localization to execute multiple steps in this catabolic process. Here, we screen for phosphoinositide phosphatases that influence autophagy in Drosophila and identify CG3530. CG3530 is homologous to the human MTMR6 subfamily of myotubularin-related 3-phosphatases, and therefore, we named it dMtmr6. dMtmr6, which is required for development and viability in Drosophila, functions as a regulator of autophagic flux in multiple Drosophila cell types. The MTMR6 family member MTMR8 has a similar function in autophagy of higher animal cells. Decreased dMtmr6 and MTMR8 function results in autophagic vesicle accumulation and influences endolysosomal homeostasis.

miR-99a-5p Regulates the Proliferation and Differentiation of Skeletal Muscle Satellite Cells by Targeting MTMR3 in Chicken

Noncoding RNAs, especially microRNAs (miRNAs), have been reported to play important roles during skeletal muscle development and regeneration. Our previous sequencing data revealed that miR-99a-5p is one of the most abundant miRNAs in chicken breast muscle. The purpose of this study was to reveal the regulatory mechanism of miR-99a-5p in the proliferation and differentiation of chicken skeletal muscle satellite cells (SMSCs). Through the investigation of cell proliferation activity, cell cycle progression, and 5-ethynyl-29-deoxyuridine (EdU) assay, we found that miR-99a-5p can significantly promote the proliferation of SMSCs. Moreover, we found that miR-99a-5p can inhibit myotube formation by decreasing the expression of muscle cell differentiation marker genes. After miR-99a-5p target gene scanning, we confirmed that miR-99a-5p directly targets the 3′ untranslated region (UTR) of myotubularin-related protein 3 (MTMR3) and regulates its expression level during chicken SMSC proliferation and differentiation. We also explored the role of MTMR3 in muscle development and found that its knockdown significantly facilitates the proliferation but represses the differentiation of SMSCs, which is opposite to the effects of miR-99a-5p. Overall, we demonstrated that miR-99a-5p regulates the proliferation and differentiation of SMSCs by targeting MTMR3.

Identification and biological evaluation of novel benzothiazole derivatives bearing a pyridine-semicarbazone moiety as apoptosis inducers via activation of procaspase-3 to caspase-3

Three series of compounds were designed, synthesized and evaluated for their in vitro anticancer activity against a procaspase-3 over-expression cancer cell line (U937) and a procaspase-3 no-expression cancer cell line (MCF-7) to rule out off-target effects. Biological evaluation led to the identification of a series of benzothiazole derivatives bearing a pyridine-semicarbazone moiety, 8j and 8k, with promising anticancer activity and remarkable selectivity. Further mechanism studies revealed that compounds 8j and 8k could induce apoptosis of cancer cells by activating procaspase-3 to caspase-3, and compound 8k exhibited the strongest procaspase-3 activation activity. Structure-activity relationships (SARs) revealed that the presence of benzothiazole and an N,N,O-donor set is crucial for the anticancer activity and selectivity, and reducing the electron density of the N,N,O-donor set results in a dramatic decline in the anticancer activity and selectivity. Furthermore, toxicity evaluation (zebrafish) in vivo and metabolic stability studies (human, rat and mouse liver microsomes) were performed to provide reliable guidance for further PK/PD studies in vivo.

Myotubularin-related protein 7 inhibits insulin signaling in colorectal cancer

Phosphoinositide (PIP) phosphatases such as myotubularins (MTMs) inhibit growth factor receptor signaling. However, the function of myotubularin-related protein 7 (MTMR7) in cancer is unknown. We show that MTMR7 protein was down-regulated with increasing tumor grade (G), size (T) and stage (UICC) in patients with colorectal cancer (CRC) (n=1786). The presence of MTMR7 in the stroma correlated with poor prognosis, whereas MTMR7 expression in the tumor was not predictive for patients' survival. Insulin reduced MTMR7 protein levels in human CRC cell lines, and CRC patients with type 2 diabetes mellitus (T2DM) or loss of imprinting (LOI) of insulin-like growth factor 2 (IGF2) had an increased risk for MTMR7 loss. Mechanistically, MTMR7 lowered PIPs and inhibited insulin-mediated AKT-ERK1/2 signaling and proliferation in human CRC cell lines. MTMR7 provides a novel link between growth factor signaling and cancer, and may thus constitute a potential marker or drug target for human CRC.

Gene Expression Profiles of Human Phosphotyrosine Phosphatases Consequent to Th1 Polarisation and Effector Function

Phosphotyrosine phosphatases (PTPs) constitute a complex family of enzymes that control the balance of intracellular phosphorylation levels to allow cell responses while avoiding the development of diseases. Despite the relevance of CD4 T cell polarisation and effector function in human autoimmune diseases, the expression profile of PTPs during T helper polarisation and restimulation at inflammatory sites has not been assessed. Here, a systematic analysis of the expression profile of PTPs has been carried out during Th1-polarising conditions and upon PKC activation and intracellular raise of Ca²⁺ in effector cells. Changes in gene expression levels suggest a previously nonnoted regulatory role of several PTPs in Th1 polarisation and effector function. A substantial change in the spatial compartmentalisation of ERK during T cell responses is proposed based on changes in the dose of cytoplasmic and nuclear MAPK phosphatases. Our study also suggests a regulatory role of autoimmune-related PTPs in controlling T helper polarisation in humans. We expect that those PTPs that regulate T helper polarisation will constitute potential targets for intervening CD4 T cell immune responses in order to generate new therapies for the treatment of autoimmune diseases.

The PtdIns3-phosphatase MTMR3 interacts with mTORC1 and suppresses its activity

Macroautophagy is a major intracellular degradation system. We previously reported that overexpression of phosphatase-deficient MTMR3, a member of the myotubularin phosphatidylinositol (PI) 3-phosphatase family, leads to induction of autophagy. In this study, we found that MTMR3 interacted with mTORC1, an evolutionarily conserved serine/threonine kinase complex, which regulates cell growth and autophagy in response to environmental stimuli. Furthermore, overexpression of MTMR3 inhibited mTORC1 activity. The N-terminal half of MTMR3, including the PH-G and phosphatase domains, was necessary and sufficient for these effects. Phosphatase-deficient MTMR3 provided more robust suppression of mTORC1 activity than wild-type MTMR3. Furthermore, phosphatase-deficient full length MTMR3 and the phosphatase domain alone were localized to the Golgi. These results suggest a new regulatory mechanism of mTORC1 in association with PI3P.

Zebrafish Lbh-like Is Required for Otx2-mediated Photoreceptor Differentiation

The homeobox transcription factor orthodenticle homolog 2 (otx2) is supposed as an organizer that orchestrates a transcription factor network during photoreceptor development. However, its regulation in the process remains unclear. In this study, we have identified a zebrafish limb bud and heart-like gene (lbh-like), which is expressed initially at 30 hours post fertilization (hpf) in the developing brain and eyes. Lbh-like knockdown by morpholinos specifically inhibits expression of multiple photoreceptor-specific genes, such as opsins, gnat1, gnat2 and irbp. Interestingly, otx2 expression in the morphants is not significantly reduced until 32 hpf when lbh-like begins to express, but its expression level in 72 hpf morphants is higher than that in wild type embryos. Co-injection of otx2 and its downstream target neuroD mRNAs can rescue the faults in eyes of Lbh-like morphants. Combined with the results of promoter-reporter assay, we suggest that lbh-like is a new regulator of photoreceptor differentiation directly through affecting otx2 expression in zebrafish. Furthermore, knockdown of lbh-like increases the activity of Notch pathway and perturbs the balance among proliferation, differentiation and survival of photoreceptor precursors.

No evidence for AID/MBD4-coupled DNA demethylation in zebrafish embryos

The mechanisms responsible for active DNA demethylation remain elusive in Metazoa. A previous study that utilized zebrafish embryos provided a potent mechanism for active demethylation in which three proteins, AID, MBD4, and GADD45 are involved. We recently found age-dependent DNA hypomethylation in zebrafish, and it prompted us to examine if AID and MBD4 could be involved in the phenomenon. Unexpectedly, however, we found that most of the findings in the previous study were not reproducible. First, the injection of a methylated DNA fragment into zebrafish eggs did not affect either the methylation of genomic DNA, injected methylated DNA itself, or several loci tested or the expression level of aid, which has been shown to play a role in demethylation. Second, aberrant methylation was not observed at certain CpG islands following the injection of antisense morpholino oligonucleotides against aid and mbd4. Furthermore, we demonstrated that zebrafish MBD4 cDNA lacked a coding region for the methyl-CpG binding domain, which was assumed to be necessary for guidance to target regions. Taken together, we concluded that there is currently no evidence to support the proposed roles of AID and MBD4 in active demethylation in zebrafish embryos.

MTM-6, a phosphoinositide phosphatase, is required to promote synapse formation in Caenorhabditis elegans

Forming the proper number of synapses is crucial for normal neuronal development. We found that loss of function of the phosphoinositide phosphatase mtm-6 results in a reduction in the number of synaptic puncta. The reduction in synapses is partially the result of MTM-6 regulation of the secretion of the Wnt ligand EGL-20 from cells in the tail and partially the result of neuronal action. MTM-6 shows relative specificity for EGL-20 over the other Wnt ligands. We suggest that the ability of MTM-6 to regulate EGL-20 secretion is a function of its expression pattern. We conclude that regulation of secretion of different Wnt ligands can use different components. Additionally, we present a novel neuronal function for MTM-6.

Identification of the crucial molecular events during the large-scale myoblast fusion in sheep

It is well known that in sheep most myofibers are formed before birth; however, the crucial myogenic stage and the cellular and molecular mechanisms underpinning phenotypic variation of fetal muscle development remain to be ascertained. We used histological, microarray, and quantitative real-time PCR (qPCR) methods to examine the developmental characteristics of fetal muscle at 70, 85, 100, 120, and 135 days of gestation in sheep. We show that day 100 is an important checkpoint for change in muscle transcriptome and histomorphology in fetal sheep and that the period of 85–100 days is the vital developmental stage for large-scale myoblast fusion. Furthermore, we identified the cis-regulatory motifs for E2F1 or MEF2A in a list of decreasingly or increasingly expressed genes between 85 and 100 days, respectively. Further analysis demonstrated that the mRNA and phosphorylated protein levels of E2F1 and MEF2A significantly declined with myogenic progression in vivo and in vitro. qRT-PCR analysis indicated that PI3K and FST, as targets of E2F1, may be involved in myoblast differentiation and fusion and that downregulation of MEF2A contributes to transition of myofiber types by differential regulation of the target genes involved at the stage of 85–100 days. We clarify for the first time the timing of myofiber proliferation and development during gestation in sheep, which would be beneficial to meat sheep production. Our findings present a repertoire of gene expression in muscle during large-scale myoblast fusion at transcriptome-wide level, which contributes to elucidate the regulatory network of myogenic differentiation.

Apolipoprotein C1 regulates epiboly during gastrulation in zebrafish

Apolipoprotein C1 (Apoc1) is associated with lipoprotein metabolism, but its physiological role during embryogenesis is largely unknown. We reveal a new function of Apoc1b, a transcript isoform of Apoc1, in epiboly during zebrafish gastrulation. Apoc1b is expressed in yolk syncytial layers and in deep cells of the ventral and lateral region of the embryos. It displays a radial gradient with high levels in the interior layer and low levels in the superficial layer. Knockdown of Apoc1b by injecting antisense morpholino (MO) caused the epiboly arrest in deep cells. Moreover, we show that the radial intercalation and the radial gradient distribution of E-cadherin are disrupted both in Apoc1b knockdown and overexpressed embryos. Therefore, Apoc1b controls epiboly via E-cadherin-mediated radial intercalation in a gradient-dependent manner.

Phosphoinositides: tiny lipids with giant impact on cell regulation

Phosphoinositides (PIs) make up only a small fraction of cellular phospholipids, yet they control almost all aspects of a cell's life and death. These lipids gained tremendous research interest as plasma membrane signaling molecules when discovered in the 1970s and 1980s. Research in the last 15 years has added a wide range of biological processes regulated by PIs, turning these lipids into one of the most universal signaling entities in eukaryotic cells. PIs control organelle biology by regulating vesicular trafficking, but they also modulate lipid distribution and metabolism via their close relationship with lipid transfer proteins. PIs regulate ion channels, pumps, and transporters and control both endocytic and exocytic processes. The nuclear phosphoinositides have grown from being an epiphenomenon to a research area of its own. As expected from such pleiotropic regulators, derangements of phosphoinositide metabolism are responsible for a number of human diseases ranging from rare genetic disorders to the most common ones such as cancer, obesity, and diabetes. Moreover, it is increasingly evident that a number of infectious agents hijack the PI regulatory systems of host cells for their intracellular movements, replication, and assembly. As a result, PI converting enzymes began to be noticed by pharmaceutical companies as potential therapeutic targets. This review is an attempt to give an overview of this enormous research field focusing on major developments in diverse areas of basic science linked to cellular physiology and disease.

Lipid phosphatases identified by screening a mouse phosphatase shRNA library regulate T-cell differentiation and protein kinase B AKT signaling

Screening a complete mouse phosphatase lentiviral shRNA library using high-throughput sequencing revealed several phosphatases that regulate CD4 T-cell differentiation. We concentrated on two lipid phosphatases, the myotubularin-related protein (MTMR)9 and -7. Silencing MTMR9 by shRNA or siRNA resulted in enhanced T-helper (Th)1 differentiation and increased Th1 protein kinase B (PKB)/AKT phosphorylation while silencing MTMR7 caused increased Th2 and Th17 differentiation and increased AKT phosphorylation in these cells. Irradiated mice reconstituted with MTMR9 shRNA-transduced bone marrow cells had an elevated proportion of T-box transcription factor T-bet expressors among their CD4 T cells. After adoptive transfer of naïve cells from such reconstituted mice, immunization resulted in a greater proportion of T-box transcription factor T-bet-expressing cells. Thus, myotubularin-related proteins have a role in controlling in vitro and in vivo Th-cell differentiation, possibly through regulation of phosphatidylinositol [3,4,5]-trisphosphate activity.

The myotubularin family of lipid phosphatases in disease and in spermatogenesis

The MTM (myotubularin)/MTMR (myotubularin-related) protein family is comprised of 15 lipid phosphatases, of which nine members are catalytically active. MTMs are known to play a fundamental role in human physiology as gene mutations can give rise to X-linked myotubular myopathy or Charcot-Marie-Tooth disease, which manifest in skeletal muscle or in peripheral neurons respectively. Interestingly, studies have shown MTMR2 and MTMR5, two MTM family members, to be highly expressed in the testis, particularly in Sertoli and germ cells, and knockout of either gene resulted in spermatogenic defects. Other studies have shown that MTMR2 functions in endocytosis and membrane trafficking. In the testis, MTMR2 interacts and co-localizes with c-Src/phospho-Src-(Tyr⁴¹⁶), a non-receptor protein tyrosine kinase that regulates the phosphorylation state of proteins at the apical ES (ectoplasmic specialization), a unique type of cell junction found between Sertoli cells and elongating/elongated spermatids. In the present review, we highlight recent findings that have made a significant impact on our understanding of this protein family in normal cell function and in disease, with the emphasis on the role of MTMs and MTMRs in spermatogenesis. We also describe a working model to explain how MTMR2 interacts with other proteins such as c-Src, dynamin 2, EPS8 (growth factor receptor pathway substrate 8) and ARP2/3 (actin-related protein 2/3) at the apical ES and the apical TBC (tubulobulbar complex; tubular-like invaginations that function in the disassembly of the apical ES and in the recycling of its components) to regulate spermiation at late stage VIII of the seminiferous epithelial cycle.

The benefits of using clickers in small-enrollment seminar-style biology courses

Although the use of clickers and peer discussion is becoming common in large-lecture undergraduate biology courses, their use is limited in small-enrollment seminar-style courses. To investigate whether facilitating peer discussion with clickers would add value to a small-enrollment seminar-style course, we evaluated their usefulness in an 11-student Embryology course at the University of Colorado, Boulder. Student performance data, observations of peer discussion, and interviews with students revealed that adding clickers to a small-enrollment course 1) increases the chance students will do the required reading before class, 2) helps the instructor engage all students in the class, and 3) gives students a focused opportunity to share thinking and to learn from their peers.

Mtmr8 is essential for vasculature development in zebrafish embryos

Background

Embryonic morphogenesis of vascular and muscular systems is tightly coordinated, and a functional cooperation of Mtmr8 with PI3K in actin filament modeling and muscle development has been revealed in zebrafish. Here, we attempt to explore the function of Mtmr8 in vasculature development parallel to its function in muscle development.

Results

During early stage of somitogenesis, mtmr8 expression was detected in both somitic mesodem and ventral mesoderm. Knockdown of mtmr8 by morpholino impairs arterial endothelial marker expression, and results in endothelial cell reduction and vasculogenesis defects, such as retardation in intersegmental vessel development and interruption of trunk dorsal aorta. Moreover, mtmr8 morphants show loss of arterial endothelial cell identity in dorsal aorta, which is effectively rescued by low concentration of PI3K inhibitor, and by over-expression of dnPKA mRNA or vegf mRNA. Interestingly, mtmr8 expression is up-regulated when zebrafish embryos are treated with specific inhibitor of Hedgehog pathway that abolishes arterial marker expression.

Conclusion

These data indicate that Mtmr8 is essential for vasculature development in zebrafish embryos, and may play a role in arterial specification through repressing PI3K activity. It is suggested that Mtmr8 should represent a novel element of the Hedgehog/PI3K/VEGF signaling cascade that controls arterial specification.

Fish-specific duplicated dmrt2b contributes to a divergent function through Hedgehog pathway and maintains left-right asymmetry establishment function

Gene duplication is thought to provide raw material for functional divergence and innovation. Fish-specific dmrt2b has been identified as a duplicated gene of the dmrt2a/terra in fish genomes, but its function has remained unclear. Here we reveal that Dmrt2b knockdown zebrafish embryos display a downward tail curvature and have U-shaped somites. Then, we demonstrate that Dmrt2b contributes to a divergent function in somitogenesis through Hedgehog pathway, because Dmrt2b knockdown reduces target gene expression of Hedgehog signaling, and also impairs slow muscle development and neural tube patterning through Hedgehog signaling. Moreover, the Dmrt2b morphants display defects in heart and visceral organ asymmetry, and, some lateral-plate mesoderm (LPM) markers expressed in left side are randomized. Together, these data indicate that fish-specific duplicated dmrt2b contributes to a divergent function in somitogenesis through Hedgehog pathway and maintains the common function for left-right asymmetry establishment.