Pparα deficiency inhibits the proliferation of neuronal and glial precursors in the zebrafish central nervous system.

BACKGROUND: Many molecules and signaling pathways involved in neural development play a role in neurodegenerative diseases and brain tumor progression. Peroxisome proliferator-activated receptor (PPAR) proteins regulate the differentiation of tissues and the progression of many diseases. However, the role of these proteins in neural development is unclear. RESULTS: We examined the function of Pparα in the neural development of zebrafish. Two duplicate paralogs for mammalian PPARA/Ppara, namely pparaa and pparab, are present in the zebrafish genome. Both pparaa and pparab are expressed in the developing central nervous system in zebrafish embryos. Inhibiting the function of Pparα by using either the PPARα/Pparα antagonist GW6471 or pparaa or pparab truncated constructs produced identical phenotypes, which were sufficient to reduce the proliferation of neuronal and glial precursor cells without affecting the formation of neural progenitors. CONCLUSIONS: We demonstrated that both Pparαa and Pparαb proteins are essential regulators of the proliferation of neuronal and glial precursors. This study provides a better understanding of the functions of PPARα/Pparα in neural development and further expands our knowledge of the potential role of PPARα/Pparα in neurological disorders and brain tumors. Developmental Dynamics 247:1264-1275, 2018. © 2018 Wiley Periodicals, Inc.

Dtx2 deficiency induces ependymo-radial glial cell proliferation and improves spinal cord motor function recovery.

Traumatic injury to the spinal cord can lead to significant, permanent disability. Mammalian spinal cords are not capable of regeneration; in contrast, adult zebrafish are capable of such regeneration, fully recovering motor function. Understanding the mechanisms underlying zebrafish neuroregeneration may provide useful information regarding endogenous regenerative potential and aid in the development of therapeutic strategies in humans. DTXs regulate a variety of cellular processes. However, their role in neural regeneration has not been described. We found that zebrafish dtx2, encoding Deltex E3 ubiquitin ligase 2, is expressed in ependymo-radial glial cells in the adult spinal cord. After spinal cord injury, the heterozygous dtx2 mutant fish motor function recovered quicker than that of the wild-type controls. The mutant fish displayed increased ependymo-radial glial cell proliferation and augmented motor neuron formation. Moreover, her gene expression, downstream of Notch signaling, increased in Dtx2 mutants. Notch signaling inactivation by dominant-negative Rbpj abolished the increased ependymo-radial glia proliferation caused by Dtx2 deficiency. These results indicate that ependymo-radial glial proliferation is induced by Dtx2 deficiency, by activating Notch-Rbpj signaling to improve spinal cord regeneration and motor function recovery.

Etv5a Suppresses Neural Progenitor Cell Proliferation by Inhibiting sox2 Transcription.

Neural progenitor cells are self-renewable, proliferative, and multipotent cell populations that generate diverse types of neurons and glia to build the nervous system. Transcription factors play critical roles in regulating various cellular processes; however, the transcription factors that regulate the development of neural progenitors are yet to be identified. In the present study, we demonstrated that zebrafish etv5a is expressed in the neural progenitor cells of the neuroectoderm. Downregulation of endogenous Etv5a function by etv5a morpholino or an etv5a dominant-negative variant increased the proliferation of sox2-positive neural progenitor cells, accompanied by inhibition of neurogenesis and gliogenesis. These phenotypes in Etv5a-depleted embryos could be rescued by a co-injection with etv5a cRNA. Etv5a overexpression reduced sox2 expression. Direct binding of Etv5a to the regulatory elements of sox2 was affirmed by chromatin immunoprecipitation. These data revealed that Etv5a directly suppressed sox2 expression to reduce the proliferation of neural progenitor cells. In addition, the expression of foxm1, a putative target gene of Etv5a and a direct upstream transcription factor of sox2, was upregulated in Etv5a-deficient embryos. Moreover, the suppression of Foxm1 function by the foxm1 dominant-negative construct nullified the phenotype of upregulated sox2 expression caused by Etv5a deficiency. Overall, our results indicated that Etv5a regulates the expression of sox2 via direct binding to the sox2 promoter and indirect regulation by inhibiting foxm1 expression. Hence, we revealed the role of Etv5a in the transcriptional hierarchy that regulates the proliferation of neural progenitor cells.

RGS2 Suppresses Melanoma Growth via Inhibiting MAPK and AKT Signaling Pathways.

BACKGROUND/AIM: This study aimed to explore RGS2 as a regulator of melanoma cell growth. MATERIALS AND METHODS: Effect of RGS2 over-expression was analyzed in three melanoma cell lines, and Rgs2 knockdown was performed in zebrafish. RESULTS: RGS2 was differentially expressed among the cell lines. In B16F10 cells, RGS2 over-expression inhibited MAPK and AKT activation, and prevented cell growth. A similar outcome was observed in A375 cells, but the MAPK signals were not suppressed. In A2058 cells, RGS2 repressed AKT activation, but without affecting cell growth. Moreover, MAPK and AKT constitutive activation abolished the RGS2 inhibitory effect on B16F10 cell growth. Rgs2 knockdown caused ectopic melanocyte differentiation, and promoted MAPK and AKT activation in zebrafish embryos. CONCLUSION: RGS2 prevents melanoma cell growth by inhibiting MAPK and AKT, but this effect depends on the overall cell genetic landscape. Further studies are warranted to investigate the anticancer therapeutic potential of RGS2 for melanoma.

PLA2G6 mutations cause motor dysfunction phenotypes of young-onset dystonia-parkinsonism type 14 and can be relieved by DHA treatment in animal models.

Parkinson's disease (PD), the most common neurodegenerative motor disorder, is currently incurable. Although many studies have provided insights on the substantial influence of genetic factors on the occurrence and development of PD, the molecular mechanism underlying the disease is largely unclear. Previous studies have shown that point mutations in the phospholipase A2 group VI gene (PLA2G6) correlate with young-onset dystonia-parkinsonism type 14 (PARK14). However, limited information is available regarding the pathogenic role of this gene and the mechanism underlying its function. To study the role of PLA2G6 mutations, we first used zebrafish larvae to screen six PLA2G6 mutations and revealed that injection of D331Y, T572I, and R741Q mutation constructs induced phenotypes such as motility defects and reduction in dopaminergic neurons. The motility defects could be alleviated by treatment with L-3, 4-dihydroxyphenylalanine (L-dopa), indicating that these mutations are pathological for PARK14 symptoms. Furthermore, the injection of D331Y and T572I mutation constructs reduced phospholipase activity of PLA2G6 and its lipid metabolites, which confirmed that these two mutations are loss-of-function mutations. Metabolomic analysis revealed that D331Y or T572I mutation led to higher phospholipid and lower docosahexaenoic acid (DHA) levels, indicating that reduced DHA levels are pathological for defective motor functions. Further, a dietary DHA supplement relieved the motility defects in PLA2G6D331Y/D331Y knock-in mice. This result revealed that the D331Y mutation caused defective PLA2G6 phospholipase activity and consequently reduced the DHA level, which is the pathogenic factor responsible for PARK14. The results of this study will facilitate the development of therapeutic strategies for PARK14.

Aminoacrylate intermediates in the reaction of Citrobacter freundii tyrosine phenol-lyase.

Tyrosine phenol-lyase (TPL) from Citrobacter freundii is a pyridoxal 5'-phosphate (PLP)-dependent enzyme that catalyzes the reversible hydrolytic cleavage of l-Tyr to give phenol and ammonium pyruvate. The proposed reaction mechanism for TPL involves formation of an external aldimine of the substrate, followed by deprotonation of the alpha-carbon to give a quinonoid intermediate. Elimination of phenol then has been proposed to give an alpha-aminoacrylate Schiff base, which releases iminopyruvate that ultimately undergoes hydrolysis to yield ammonium pyruvate. Previous stopped-flow kinetic experiments have provided direct spectroscopic evidence for the formation of the external aldimine and quinonoid intermediates in the reactions of substrates and inhibitors; however, the predicted alpha-aminoacrylate intermediate has not been previously observed. We have found that 4-hydroxypyridine, a non-nucleophilic analogue of phenol, selectively binds and stabilizes aminoacrylate intermediates in reactions of TPL with S-alkyl-l-cysteines, l-tyrosine, and 3-fluoro-l-tyrosine. In the presence of 4-hydroxypyridine, a new absorption band at 338 nm, assigned to the alpha-aminoacrylate, is observed with these substrates. Formation of the 338 nm peaks is concomitant with the decay of the quinonoid intermediates, with good isosbestic points at approximately 365 nm. The value of the rate constant for aminoacrylate formation is similar to k(cat), suggesting that leaving group elimination is at least partially rate limiting in TPL reactions. In the reaction of S-ethyl-l-cysteine in the presence of 4-hydroxypyridine, a subsequent slow reaction of the alpha-aminoacrylate is observed, which may be due to iminopyruvate formation. Both l-tyrosine and 3-fluoro-l-tyrosine exhibit kinetic isotope effects of approximately 2-3 on alpha-aminoacrylate formation when the alpha-(2)H-labeled substrates are used, consistent with the previously reported internal return of the alpha-proton to the phenol product. These results are the first direct spectroscopic observation of alpha-aminoacrylate intermediates in the reactions of TPL.

Role of lysine-256 in Citrobacter freundii tyrosine phenol-lyase in monovalent cation activation.

Tyrosine phenol-lyase (TPL) from Citrobacter freundii is dependent on monovalent cations, K(+) or NH(4)(+), for high activity. We have shown previously that Glu-69, which is a ligand to the bound cation, is important in monovalent cation binding and activation [Sundararaju, B., Chen, H., Shillcutt, S., and Phillips, R. S. (2000) Biochemistry 39, 8546-8555]. Lys-256 is located in the monovalent cation binding site of TPL, where it forms a hydrogen bond with a structural water bound to the cation. This lysine residue is highly conserved in sequences of TPL and the paralogue, tryptophan indole-lyase. We have now prepared K256A, K256H, K256R, and E69D/K256R mutant TPLs to probe the role of Lys-256 in monovalent cation binding and activation. K256A and K256H TPLs have low activity (k(cat)/K(m) values of 0.01-0.1%), are not activated by monovalent cations, and do not exhibit fluorescence emission at 500 nm from the PLP cofactor. In contrast, K256R TPL has higher activity (k(cat)/K(m) about 10% of wild-type TPL), is activated by K(+), and exhibits fluorescence emission from the PLP cofactor. K256A, K256H, and K256R TPLs bind PLP somewhat weaker than wild-type TPL. E69D/K256R TPL was prepared to determine if the guanidine side chain could substitute for the monovalent cation. This mutant TPL has wild-type activity with S-Et-L-Cys or S-(o-nitrophenyl)-L-Cys but has no detectable activity with L-Tyr. E69D/K256R TPL is not activated by monovalent cations and does not show PLP fluorescence. In contrast to wild-type and other mutant TPLs, PLP binding to E69D/K256R is very slow, requiring several hours of incubation to obtain 1 mol of PLP per subunit. Thus, E69D/K256R TPL appears to have altered dynamics. All of the mutant TPLs react with inhibitors, L-Ala, L-Met, and L-Phe, to form equilibrating mixtures of external aldimine and quinonoid intermediates. Thus, Lys-256 is not the base which removes the alpha-proton during catalysis. The results show that the function of Lys-256 in TPL is in monovalent cation binding and activation.