microRNA-206 modulates an Rtn4a/Cxcr4a/Thbs3a axis in newly forming somites to maintain and stabilize the somite boundary formation of zebrafish embryos

Genomic Structure, Protein Character, Phylogenic Implication, and Embryonic Expression Pattern of a Zebrafish New Member of Zinc Finger BED-Type Gene Family

We reported a new member of the C₂H₂-zinc-finger BED-type (ZBED) protein family found in zebrafish (Danio rerio). It was previously assigned as an uncharacterized protein LOC569044 encoded by the Zgc:161969 gene, the transcripts of which were highly expressed in the CNS after the spinal cord injury of zebrafish. As such, this novel gene deserves a more detailed investigation. The 2.79-kb Zgc:161969 gene contains one intron located on Chromosome 6 at 16,468,776-16,475,879 in the zebrafish genome encoding a 630-aa protein LOC569044. This protein is composed of a DNA-binding BED domain, which is highly conserved among the ZBED protein family, and a catalytic domain consisting of an α-helix structure and an hAT dimerization region. Phylogenetic analysis revealed the LOC569044 protein to be clustered into the monophyletic clade of the ZBED protein family of golden fish. Specifically, the LOC569044 protein was classified as closely related to the monophyletic clades of zebrafish ZBED4-like isoforms and ZBED isoform 2. Furthermore, Zgc:161969 transcripts represented maternal inheritance, expressed in the brain and eyes at early developmental stages and in the telencephalon ventricular zone at late developmental stages. After characterizing the LOC569044 protein encoded by the Zgc:161969 gene, it was identified as a new member of the zebrafish ZBED protein family, named the ZBEDX protein.

Quantification of Idua Enzymatic Activity Combined with Observation of Phenotypic Change in Zebrafish Embryos Provide a Preliminary Assessment of Mutated idua Correlated with Mucopolysaccharidosis Type I

Mucopolysaccharidosis type I (MPS I) is an inherited autosomal recessive disease resulting from mutation of the α-l-Iduronidase (IDUA) gene. New unknown mutated nucleotides of idua have increasingly been discovered in newborn screening, and remain to be elucidated. In this study, we found that the z-Idua enzymatic activity of zebrafish idua-knockdown embryos was reduced, resulting in the accumulation of undegradable metabolite of heparin sulfate, as well as increased mortality and defective phenotypes similar to some symptoms of human MPS I. After microinjecting mutated z-idua-L346R, -T364M, -E398-deleted, and -E540-frameshifted mRNAs, corresponding to mutated human IDUA associated with MPS I, into zebrafish embryos, no increase in z-Idua enzymatic activity, except of z-idua-E540-frameshift-injected embryos, was noted compared with endogenous z-Idua of untreated embryos. Defective phenotypes were observed in the z-idua-L346R-injected embryos, suggesting that failed enzymatic activity of mutated z-Idua-L346R might have a dominant negative effect on endogenous z-Idua function. However, defective phenotypes were not observed in the z-idua-E540-frameshifted-mRNA-injected embryos, which provided partial enzymatic activity. Based on these results, we suggest that the z-Idua enzyme activity assay combined with phenotypic observation of mutated-idua-injected zebrafish embryos could serve as an alternative platform for a preliminary assessment of mutated idua not yet characterized for their role in MPS I.

Cerebroventricular Injection of Pgk1 Attenuates MPTP-Induced Neuronal Toxicity in Dopaminergic Cells in Zebrafish Brain in a Glycolysis-Independent Manner

Parkinson’s disease (PD) is characterized by the degeneration of dopaminergic neurons. While extracellular Pgk1 (ePgk1) is reported to promote neurite outgrowth, it remains unclear if it can affect the survival of dopaminergic cells. To address this, we employed cerebroventricular microinjection (CVMI) to deliver Pgk1 into the brain of larvae and adult zebrafish treated with methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as a PD-like model. The number of dopamine-producing cells in ventral diencephalon clusters of Pgk1-injected, MPTP-treated embryos increased over that of MPTP-treated embryos. Swimming distances of Pgk1-injected, MPTP-treated larvae and adult zebrafish were much longer compared to MPTP-treated samples. The effect of injected Pgk1 on both dopamine-producing cells and locomotion was time- and dose-dependent. Indeed, injected Pgk1 could be detected, located on dopamine neurons. When the glycolytic mutant Pgk1, Pgk1-T378P, was injected into the brain of MPTP-treated zebrafish groups, the protective ability of dopaminergic neurons did not differ from that of normal Pgk1. Therefore, ePgk1 is functionally independent from intracellular Pgk1 serving as an energy supplier. Furthermore, when Pgk1 was added to the culture medium for culturing dopamine-like SH-SY5Y cells, it could reduce the ROS pathway and apoptosis caused by the neurotoxin MPP⁺. These results show that ePgk1 benefits the survival of dopamine-producing cells and decreases neurotoxin damage.

What we can learn from embryos to understand the mesenchymal-to-epithelial transition in tumor progression

Epithelial plasticity involved the terminal and transitional stages that occur during epithelial-to-mesenchymal transition (EMT) and mesenchymal-to-epithelial transition (MET), both are essential at different stages of early embryonic development that have been co-opted by cancer cells to undergo tumor metastasis. These processes are regulated at multiple instances, whereas the post-transcriptional regulation of key genes mediated by microRNAs is gaining major attention as a common and conserved pathway. In this review, we focus on discussing the latest findings of the cellular and molecular basis of the less characterized process of MET during embryonic development, with special attention to the role of microRNAs. Although we take in consideration the necessity of being cautious when extrapolating the obtained evidence, we propose some commonalities between early embryonic development and cancer progression that can shed light into our current understanding of this complex event and might aid in the design of specific therapeutic approaches.

Extracellular Pgk1 enhances neurite outgrowth of motoneurons through Nogo66/NgR-independent targeting of NogoA

NogoA inhibits neurite outgrowth of motoneurons (NOM) through interaction with its receptors, Nogo66/NgR. Inhibition of Nogo receptors rescues NOM, but not to the extent exhibited by NogoA-knockout mice, suggesting the presence of other pathways. We found that NogoA-overexpressing muscle cells reduced phosphoglycerate kinase 1 (Pgk1) secretion, resulting in inhibiting NOM. Apart from its glycolytic role and independent of the Nogo66 pathway, extracellular Pgk1 stimulated NOM by triggering a reduction of p-Cofilin-S3, a growth cone collapse marker, through decreasing a novel Rac1-GTP/p-Pak1-T423/p-P38-T180/p-MK2-T334/p-Limk1-S323/p-Cofilin-S3 molecular pathway. Not only did supplementary Pgk1 enhance NOM in defective cells, but injection of Pgk1 rescued denervation in muscle-specific NogoA-overexpression of zebrafish and an Amyotrophic Lateral Sclerosis mouse model, SOD1 G93A. Thus, Pgk1 secreted from muscle is detrimental to motoneuron neurite outgrowth and maintenance.

Conditional Overexpression of rtn4al in Muscle of Adult Zebrafish Displays Defects Similar to Human Amyotrophic Lateral Sclerosis

The protein level of muscle-specific human NogoA is abnormally upregulated in amyotrophic lateral sclerosis (ALS) mice and patients. On the other hand, while the presence of miR-206 in muscle cells delays onset and death in ALS, the relationship between these two phenomena remains unclear. Mammalian NogoA protein, also known as Reticulon 4a (Rtn4a), plays an important role in inhibiting the outgrowth of motor neurons. Our group previously identified zebrafish rtn4al as the target gene of miR-206 and found that knockdown of miR-206 increases rtn4al mRNA and Rtn4al protein in zebrafish embryos. It can be concluded from these results that neurite outgrowth of motor neurons is inhibited by Rtn4a1, which is entirely consistent with overexpression of either human NogoA or zebrafish homolog Rtn4al. Since an animal model able to express NogoA/rtn4al at the mature stage is unavailable, we generated a zebrafish transgenic line, Tg(Zα:TetON-Rtn4al), which conditionally and specifically overexpresses Rtn4al in the muscle tissue. After doxycycline induction, adult zebrafish displayed denervation at neuromuscular junction during the first week, then muscle disintegration and split myofibers during the third week, and, finally, significant weight loss in the sixth week. These results suggest that this zebrafish transgenic line, representing the inducible overexpression of Rtn4a1 in muscle, may provide an alternative animal model with which to study ALS because it exhibits ALS-like phenotype.

Mir-206 partially rescues myogenesis deficiency by inhibiting CUGBP1 accumulation in the cell models of myotonic dystrophy

Objectives: In this study, we aim to determine how CUG-expansion and the abundance of Celf1 regulates normal myocyte differentiation and reveal the role ofmiR-206 in myotonic dystrohy and explore a possible gene therapy vector. Methods: we set up CUG-expansion and Celf1 overexpression C2C12 cell models to imitate the myocyte differentiation defects of DM1, then transfected AdvmiR-206 into cell models, tested the level of myogenic markers MyoD, MyoG, Mef2c, Celf1 by RT-PCRand Western Blotting, detected myotube formation by myosin heavy chain immunostaining. Result: 3'-UTR CUG-expansion leads to myotube defects and impaired myoblasts differentiation. Overexpression of Celf1 inhibits myoblast differentiation and impairs differentiation. Knockdown of Celf1 partially rescues differentiation defects of myoblasts harboring CUG-expansion. miR-206 incompletely reverses myoblast differentiation inhibition induced by CUG-expansion and partially recuses myoblast differentiation defects induced by Celf1 overexpression. Conclusions: Ectopic miR-206 mimicking the endogenous temporal patterns specifically drives a myocyte program that boosts myoblast lineages, likely by promoting the expression of MyoD to rectify the myogenic deficiency by stimulating the accumulation of Celf1. Abbreviations: DMPK: (dystrophia myotonica protein kinase); 3'-UTR: (3'-untranslated region); MBNL1: (muscleblind-like [Drosophila]); DM1: (myotonic dystrophy type 1); GFP: (green fluorescent protein); RT-PCR: (quantitative reverse transcriptase-polymerase chain reaction); shRNA: (short hairpin RNA).

miR-206 is required for changes in cell adhesion that drive muscle cell morphogenesis in Xenopus laevis

MicroRNAs (miRNAs) are highly conserved small non-coding RNA molecules that post-transcriptionally regulate gene expression in multicellular organisms. Within the set of muscle-specific miRNAs, miR-206 expression is largely restricted to skeletal muscle and is found exclusively within the bony fish lineage. Although many studies have implicated miR-206 in muscle maintenance and disease, its role in skeletal muscle development remains largely unknown. Here, we examine the role of miR-206 during Xenopus laevis somitogenesis. In Xenopus laevis, miR-206 expression coincides with the onset of somitogenesis. We show that both knockdown and over-expression of miR-206 result in abnormal somite formation affecting muscle cell rotation, attachment, and elongation. In particular, our data suggests that miR-206 regulates changes in cell adhesion that affect the ability of newly formed somites to adhere to the notochord as well as to the intersomitic boundaries. Additionally, we show that β-dystroglycan and F-actin expression levels are significantly reduced, suggesting that knockdown of miR-206 levels affects cellular mechanics necessary for cell shape changes and attachments that are required for proper muscle formation.