Disruption of neuronal RHEB signaling impairs oligodendrocyte differentiation and myelination through mTORC1-DLK1 axis.

How neuronal signaling affects brain myelination remains poorly understood. We show dysregulated neuronal RHEB-mTORC1-DLK1 axis impairs brain myelination. Neuronal Rheb cKO impairs oligodendrocyte differentiation/myelination, with activated neuronal expression of the imprinted gene Dlk1. Neuronal Dlk1 cKO ameliorates myelination deficit in neuronal Rheb cKO mice, indicating that activated neuronal Dlk1 expression contributes to impaired myelination caused by Rheb cKO. The effect of Rheb cKO on Dlk1 expression is mediated by mTORC1; neuronal mTor cKO and Raptor cKO and pharmacological inhibition of mTORC1 recapitulate elevated neuronal Dlk1 expression. We demonstrate that both a secreted form of DLK1 and a membrane-bound DLK1 inhibit the differentiation of cultured oligodendrocyte precursor cells into oligodendrocytes expressing myelin proteins. Finally, neuronal expression of Dlk1 in transgenic mice reduces the formation of mature oligodendrocytes and myelination. This study identifies Dlk1 as an inhibitor of oligodendrocyte myelination and a mechanism linking altered neuronal signaling with oligodendrocyte dysfunction.

Chromosome-level genome assembly of a triploid poplar Populus alba 'Berolinensis'.

Many recent studies have provided significant insights into polyploid breeding, but limited research has been carried out on trees. The genomic information needed to understand growth and response to abiotic stress in polyploidy trees is largely unknown, but has become critical due to the threats to forests imposed by climate change. Populus alba 'Berolinensis,' also known "Yinzhong poplar," is a triploid poplar from northeast China. This hybrid triploid poplar is widely used as a landscape ornamental and in urban forestry owing to its adaptation to adverse environments and faster growth than its parental diploid. It is an artificially synthesized male allotriploid hybrid, with three haploid genomes of P. alba 'Berolinensis' originating from different poplar species, so it is attractive for studying polyploidy genomic mechanisms in heterosis. In this study, we focused on the allelic genomic interactions in P. alba 'Berolinensis,' and generated a high-quality chromosome-level genome assembly consisting of 19 allelic chromosomes. Its three haploid chromosome sets are polymorphic with an average of 25.73 nucleotide polymorphism sites per kilobase. We found that some stress-related genes such as RD22 and LEA7 exhibited sequence differences between different haploid genomes. The genome assembly has been deposited in our polyploid genome online analysis website TreeGenomes (https://www.treegenomes.com). These polyploid genome-related resources will provide a critical foundation for the molecular breeding of P. alba 'Berolinensis' and help us uncover the allopolyploidization effects of heterosis and abiotic stress resistance and traits of polyploidy species in the future.

Genome sequence and evolution of Betula platyphylla.

Betula L. (birch) is a pioneer hardwood tree species with ecological, economic, and evolutionary importance in the Northern Hemisphere. We sequenced the Betula platyphylla genome and assembled the sequences into 14 chromosomes. The Betula genome lacks evidence of recent whole-genome duplication and has the same paleoploidy level as Vitis vinifera and Prunus mume. Phylogenetic analysis of lignin pathway genes coupled with tissue-specific expression patterns provided clues for understanding the formation of higher ratios of syringyl to guaiacyl lignin observed in Betula species. Our transcriptome analysis of leaf tissues under a time-series cold stress experiment revealed the presence of the MEKK1-MKK2-MPK4 cascade and six additional mitogen-activated protein kinases that can be linked to a gene regulatory network involving many transcription factors and cold tolerance genes. Our genomic and transcriptome analyses provide insight into the structures, features, and evolution of the B. platyphylla genome. The chromosome-level genome and gene resources of B. platyphylla obtained in this study will facilitate the identification of important and essential genes governing important traits of trees and genetic improvement of B. platyphylla.

Content analysis of vitamins, dietary fibers and amino acids in a wide collection of barley (Hordeum vulgare L.) from Tibet, China.

Barley (Hordeum vulgare L.) is an important agricultural crop. Various studies on the genetic diversity, biochemical and molecular attributes on this species are known. However, information on nutritional variability in a large panel of barley cultivars is limited. Therefore, it is of interest for a quantitative analysis of vitamins, amino acids and dietary fibers in 245 barley of Tibet region in China. The coefficient of variation analysis revealed strong variation of vitamins (VB1>VB2>VE), essential amino acids (valine, histidine, methionine, lysine), non-essential amino acids (proline, tyrosine, cysteine), dietary fibers, (cellulose > lignin). Principal component analysis detected three clusters of cultivars, each with specific characteristics. However, the most nutritional cultivars were found in Cluster 3, which encompassed 52 cultivars. Distinctly, six cultivars (ZQ2000, BJX230, BJX229, BJX249, BJX191 and BJX265) were identified with highest nutritional values. This study reveals a large nutritional diversity in barley cultivars from Tibet and represents an important reference for the exploitation of these germplasm in crop improvement and breeding programmes.

Negative feedback loop between BpAP1 and BpPI/BpDEF heterodimer in Betula platyphylla × B. pendula.

MADS-box genes encode transcription factors involved in the control of many important developmental processes, especially the flower development of angiosperms. Analysis on gene regulatory relationship between MADS-box genes is useful for understanding the molecular mechanism of flower development. In this study, we focused on the regulatory relationship between MADS-box transcription factors APETALA1 (AP1) and PISTILLATA(PI)/DEFICIENS (DEF) in birch. We found that BpPI was an authentic target gene of BpAP1, and BpAP1 activated the expression of BpPI via directly binding to the CArG box motif. Functional analysis of BpPI showed that overexpression of BpPI may delay flowering via restricting flowering activators, in which BpAP1 was significantly down-regulated. We further investigated the regulatory of BpAP1 by BpPI, and found that BpPI could directly bind to the promoter of BpAP1 to restrict BpAP1 expression. In addition, we also found that BpPI could interact with its hypothetical partner BpDEF to co-regulate BpAP1 in birch. Our results suggested that overexpression of BpPI may delay flowering via restricting flowering activators, and there is a negative feedback loop between BpAP1 and BpPI/BpDEF heterodimer in birch. Our results will bring new evidences for further analysis of the molecular mechanism of flower formation in plants that produced unisexual flowers.

BpAP1 directly regulates BpDEF to promote male inflorescence formation in Betula platyphylla × B. pendula.

Flowering is a crucial process for plants that is under complex genetic control. AP1 acts as an organizer and a switch for the transition from vegetative to reproductive growth. In our previous study, we found that overexpression of BpAP1 significantly promoted the formation of male inflorescence in birch (Betula platyphlla × B. pendula). In this study, we aimed at investigating the molecular regulatory mechanism of BpAP1 during the process of male inflorescence formation in birch. We found that overexpression of BpAP1 affected the expression of many flowering-related genes, and had significant effect on B class MADS-box genes. A BpAP1-mediated gene regulatory network was constructed and B class gene BpDEF was finally predicted as a key target gene of BpAP1. Chromatin immunoprecipitation results indicated that BpAP1 could directly regulate BpDEF during the process of male inflorescence formation. Yeast one-hybrid assays and its validation in tobacco results suggested that BpAP1 regulated BpDEF via binding to a consensus DNA sequence known as CArG box. Gene function analysis of BpDEF indicated that BpDEF may function in sex-determination, and in particular specify the identity of male inflorescence in birch. Our results provide valuable clues for our understanding of the molecular mechanism of BpAP1 during the process of male inflorescence formation in birch.

The p53/miRNAs/Ccna2 pathway serves as a novel regulator of cellular senescence: Complement of the canonical p53/p21 pathway.

Aging is a multifactorial process characterized by the progressive deterioration of physiological functions. Among the multiple molecular mechanisms, microRNAs (miRNAs) have increasingly been implicated in the regulation of Aging process. However, the contribution of miRNAs to physiological Aging and the underlying mechanisms remain elusive. We herein performed high-throughput analysis using miRNA and mRNA microarray in the physiological Aging mouse, attempted to deepen into the understanding of the effects of miRNAs on Aging process at the "network" level. The data showed that various p53 responsive miRNAs, including miR-124, miR-34a and miR-29a/b/c, were up-regulated in Aging mouse compared with that in Young mouse. Further investigation unraveled that similar as miR-34a and miR-29, miR-124 significantly promoted cellular senescence. As expected, mRNA microarray and gene co-expression network analysis unveiled that the most down-regulated mRNAs were enriched in the regulatory pathways of cell proliferation. Fascinatingly, among these down-regulated mRNAs, Ccna2 stood out as a common target of several p53 responsive miRNAs (miR-124 and miR-29), which functioned as the antagonist of p21 in cell cycle regulation. Silencing of Ccna2 remarkably triggered the cellular senescence, while Ccna2 overexpression delayed cellular senescence and significantly reversed the senescence-induction effect of miR-124 and miR-29. Moreover, these p53 responsive miRNAs were significantly up-regulated during the senescence process of p21-deficient cells; overexpression of p53 responsive miRNAs or knockdown of Ccna2 evidently accelerated the cellular senescence in the absence of p21. Taken together, our data suggested that the p53/miRNAs/Ccna2 pathway might serve as a novel senescence modulator independent of p53/p21 pathway.

Dynamic m6A modification regulates local translation of mRNA in axons.

N6-methyladenosine (m6A) is a reversible modification in mRNA and has been shown to regulate processing, translation and decay of mRNA. However, the roles of m6A modification in neuronal development are still not known. Here, we found that the m6A eraser FTO is enriched in axons and can be locally translated. Axon-specific inhibition of FTO by rhein, or compartmentalized siRNA knockdown of Fto in axons led to increases of m6A levels. GAP-43 mRNA is modified by m6A and is a substrate of FTO in axons. Loss-of-function of this non-nuclear pool of FTO resulted in increased m6A modification and decreased local translation of axonal GAP-43 mRNA, which eventually repressed axon elongation. Mutation of a predicted m6A site in GAP-43 mRNA eliminated its m6A modification and exempted regulation of its local translation by axonal FTO. This work showed an example of dynamic internal m6A demethylation of non-nuclear localized mRNA by the demethylase FTO. Regulation of m6A modification of axonal mRNA by axonal FTO might be a general mechanism to control their local translation in neuronal development.

miR-194 functions as a novel modulator of cellular senescence in mouse embryonic fibroblasts.

MicroRNA-194 (miR-194), a typical p53 responsive miRNA, serves as a tumor suppressor similar as p53, and has been demonstrated to play an anti-proliferation role in various human cancers. In spite of the pivotal role of p53 during aging process, the knowledge of miR-194's contribution to cellular senescence is limited. We herein sought to explore the role of miR-194 in the replicative senescence and stress-induced senescence of mouse embryonic fibroblasts. Our results unraveled that, compared to young cells, miR-194 is highly expressed in senescent cells, and extra expression of miR-194 significantly triggers the replicative senescence of MEFs and H2 O2 -induced senescence of NIH/3T3 cells, while inhibition of miR-194 exhibited the opposite effect. We further unveiled that DNMT3A was a direct and authentic target of miR-194, which has been reported to be closely associated with cellular senescence. Taken together, our data suggest that miR-194 may significantly promote the development of cellular senescence in mouse embryonic fibroblasts, which potentially occurs through inhibiting the DNMT3A expression.

DNA damage responsive miR-33b-3p promoted lung cancer cells survival and cisplatin resistance by targeting p21WAF1/CIP1.

Cisplatin is the most potent and widespread used chemotherapy drug for lung cancer treatment. However, the development of resistance to cisplatin is a major obstacle in clinical therapy. The principal mechanism of cisplatin is the induction of DNA damage, thus the capability of DNA damage response (DDR) is a key factor that influences the cisplatin sensitivity of cancer cells. Recent advances have demonstrated that miRNAs (microRNAs) exerted critical roles in DNA damage response; nonetheless, the association between DNA damage responsive miRNAs and cisplatin resistance and its underlying molecular mechanism still require further investigation. The present study has attempted to identify differentially expressed miRNAs in cisplatin induced DNA damage response in lung cancer cells, and probe into the effects of the misexpressed miRNAs on cisplatin sensitivity. Deep sequencing showed that miR-33b-3p was dramatically down-regulated in cisplatin-induced DNA damage response in A549 cells; and ectopic expression of miR-33b-3p endowed the lung cancer cells with enhanced survival and decreased γH2A.X expression level under cisplatin treatment. Consistently, silencing of miR-33b-3p in the cisplatin-resistant A549/DDP cells evidently sensitized the cells to cisplatin. Furthermore, we identified CDKN1A (p21) as a functional target of miR-33b-3p, a critical regulator of G1/S checkpoint, which potentially mediated the protection effects of miR-33b-3p against cisplatin. In aggregate, our results suggested that miR-33b-3p modulated the cisplatin sensitivity of cancer cells might probably through impairing the DNA damage response. And the knowledge of the drug resistance conferred by miR-33b-3p has great clinical implications for improving the efficacy of chemotherapies for treating lung cancers.

MicroRNA-33 promotes the replicative senescence of mouse embryonic fibroblasts by suppressing CDK6.

MicroRNAs are a large class of tiny noncoding RNAs, which have emerged as critical regulators of gene expression, and thus are involved in multiple cellular processes, including cellular senescence. MicroRNA-33 has previously been established to exert crucial effect on cell proliferation, lipid metabolism and cholesterol metabolism. Nonetheless, the association between microRNA-33 and cellular senescence and its underlying molecular mechanism are far to be elucidated. The present study has attempted to probe into the effect of microRNA-33 on MEFs senescence. Our data unveiled that microRNA-33 was dramatically down-regulated in senescent MEFs compared to the young MEFs, and ectopic expression of microRNA-33 promoted MEFs senescence, while knock-down of microRNA-33 exhibited a protective effect against senescence phenotype. Moreover, we verified CDK6 as a direct target of microRNA-33 in mouse. Silencing of CDK6 induced the premature senescence phenotype of MEFs similarly as microRNA-33, while enforced expression of CDK6 significantly reverse the senescence-induction effect of microRNA-33. Taken together, our results suggested that microRNA-33 enhanced the replicative senescence of MEFs potentially by suppressing CDK6 expression.

The complete mitochondrial genome of Daurian ground squirrel, Spermophilus dauricus.

The mitochondrial genome sequence of Daurian ground squirrel, Spermophilus dauricus, is determined and described for the first time in this study. The genome was a total of 16 512 bp in length and had a base composition of A (32.08%), G (12.53%), C (24.35%), and T (31.04%), indicating that the percentage of A + T (63.12%) is higher than G + C (36.88%). Similar to those reported from other animal mitochondrial genomes, it possessed a typically conserved structure, including 13 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes and 1 control region (D-loop). Most of these genes were found to locate on the H-strand except for the ND6 gene and 8 tRNA genes. The phylogenetic analysis showed Spermophilus dauricus formed the sister group to the Pteromyini tribe. This mitochondrial genome sequence would supply useful genetic resources to uncover Sciuridae family evolution.

The association of APOC4 polymorphisms with premature coronary artery disease in a Chinese Han population.

BACKGROUND: Hypercholesterolemia arising from abnormal lipid metabolism is one of the critical risk factors for coronary artery disease (CAD), however the roles of genetic variants in lipid metabolism-related genes on premature CAD (≤ 60 years old) development still require further investigation. We herein genotyped four single nucleotide polymorphisms (SNPs) in lipid metabolism-related genes (rs1132899 and rs5167 in APOC4, rs1801693 and rs7765781 in LPA), aimed to shed light on the influence of these SNPs on individual susceptibility to early-onset CAD. METHODS: Genotyping of the four SNPs (rs1132899, rs5167, rs1801693 and rs7765781) was performed in 224 premature CAD cases and 297 control subjects (≤ 60 years old) using polymerase chain reaction-ligation detection reaction (PCR-LDR) method. The association of these SNPs with premature CAD was performed with SPSS software. RESULTS: Multivariate logistic regression analysis showed that C allele (OR = 1.50, P = 0.027) and CC genotype (OR = 2.84, P = 0.022) of APOC4 rs1132899 were associated with increased premature CAD risk, while the other three SNPs had no significant effect. Further stratified analysis uncovered a more evident association with the risk of premature CAD among male subjects (C allele, OR = 1.65, and CC genotype, OR = 3.33). CONCLUSIONS: Our data provides the first evidence that APOC4 rs1132899 polymorphism was associated with an increased risk of premature CAD in Chinese subjects, and the association was more significant among male subjects.

Next-generation transcriptome analysis in transgenic birch overexpressing and suppressing APETALA1 sheds lights in reproduction development and diterpenoid biosynthesis.

KEY MESSAGE: Overexpression of BpAP1 could cause early flowering in birch. BpAP1 affected the expression of many flowering-related unigenes and diterpenoid biosynthesis in transgenic birch, and BpPI was a putative target gene of BpAP1. APETALA1 (AP1) is an MADS-box transcription factor that is involved in the flowering process in plants and has been a focus of genetic studies examining flower development. Here, we carried out transcriptome analysis of birch (Betula platyphylla Suk.), including BpAP1 overexpression lines, BpAP1 suppression lines, and non-transgenic line (NT). Compared with NT, we detected 8302 and 7813 differentially expressed unigenes in 35S::BpAP1 and 35S::BpAP1RNAi transgenic lines, respectively. Overexpression and suppression of BpAP1 in birch affected diterpenoid biosynthesis and altered expression of many flowering-related unigenes. Moreover, combining information from the RNA-seq database and the birch genome, we predicted downstream target genes of BpAP1. Among the 166 putative target genes of BpAP1, there was a positive correlation between BpAP1 and BpPI. These results provide references for further examining the relationship between BpAP1 and its target genes, and reveal that BpAP1 functions as a transcription regulator in birch.

Functional characterization of CCR in birch (Betula platyphylla × Betula pendula) through overexpression and suppression analysis.

We cloned a Cinnamoyl-CoA Reductase gene (BpCCR1) from an apical meristem and first internode of Betula platyphylla and characterized its functions in lignin biosynthesis, wood formation and tree growth through transgenic approaches. We generated overexpression and suppression transgenic lines and analyzed them in comparison with the wild-type in terms of lignin content, anatomical characteristics, height and biomass. We found that BpCCR1 overexpression could increase lignin content up to 14.6%, and its underexpression decreased lignin content by 6.3%. Surprisingly, modification of BpCCR1 expression led to conspicuous changes in wood characteristics, including xylem vessel number and arrangement, and secondary wall thickness. The growth of transgenic trees in terms of height was also significantly influenced by the modification of BpCCR1 genes. We discuss the functions of BpCCR1 in the context of a phylogenetic tree built with CCR genes from multiple species.

Overexpression of BpAP1 induces early flowering and produces dwarfism in Betula platyphylla × Betula pendula.

The involvement of APETALA1 (AP1) in the flowering transition has been the focus of much research. Here, we produced Betula platyphylla × Betula pendula (birch) lines that overexpressed BpAP1 using Agrobacterium-mediated transformation; we obtained five independent 35S::BpAP1 transgenic lines. Polymerase chain reaction (PCR), Southern, northern and western analyses were used to identify the transformants. As determined by quantitative real-time PCR (qRT-PCR), BpAP1 expression in roots, shoots, leaves and terminal buds of 35S::BpAP1 transgenic lines was significantly higher than that in the wild type (WT, P < 0.01). The average height of 2-year-old 35S::BpAP1 plants was significantly lower (41.17%) than that of non-transgenic plants. In the 35S::BpAP1 lines, inflorescences emerged successively beginning 2 months after transplanting. In addition, the length-diameter ratio of fully developed male and female inflorescences were both significantly less than those of the WT (P < 0.05), i.e. the morphological characteristic was stubby. The male inflorescences emerged early, with empty, draped anthers, and pollen was rarely produced, whereas the female floret structure was not different from WT. The pistils developed normally and could accept pollen, leading to the production of hybrid progeny (F1 ). F1 plants completed flowering within only 1 year after sowing. We demonstrate that BpAP1 can be inherited through sexual reproduction. Overexpression of BpAP1 caused early flowering and dwarfism; these lines had an obviously shortened juvenile phase. These results greatly increase our understanding of the mechanisms underlying the flowering transition and enhance genetic studies of birch traits, and they open up new possibilities for the breeding of birch and other woody plants.