Large-scale long terminal repeat insertions produced a significant set of novel transcripts in cotton

Genomic analysis has revealed that the 1,637-Mb Gossypium arboreum genome contains approximately 81%transposable elements(TEs),while only 57%of the 735-Mb G.raimondii genome is occupied by TEs.In this study,we investigated whether there were unknown transcripts associated with TE or TE fragments and,if so,how these new transcripts were evolved and regulated.As sequence depths increased from 4 to 100 G,a total of 10,284 novel intergenic transcripts(intergenic genes)were discovered.On average,approximately 84%of these intergenic transcripts possibly overlapped with the long terminal repeat(LTR)insertions in the otherwise untranscribed intergenic regions and were expressed at relatively low levels.Most of these intergenic transcripts possessed no transcription activation markers,while the majority of the regular genic genes possessed at least one such marker.Genes without transcription activation markers formed their+1 and-1 nucleosomes more closely(only(117±1.4)bp apart),while twice as big spaces(approximately(403.5±46.0)bp apart)were detected for genes with the activation markers.The analysis of 183 previously assembled genomes across three different kingdoms demonstrated systematically that intergenic transcript numbers in a given genome correlated positively with its LTR content.Evolutionary analysis revealed that genic genes originated during one of the whole-genome duplication events around 137.7million years ago(MYA)for all eudicot genomes or 13.7 MYA for the Gossypium family,respectively,while the intergenic transcripts evolved around 1.6 MYA,resultant of the last LTR insertion.The characterization of these low-transcribed intergenic transcripts can facilitate our understanding of the potential biological roles played by LTRs during speciation and diversifications.

An Experimental Model for Screening Anti-AIDS Drugs with Bovine Immunodeficiency Virus

The assays for bovine immunodeficiency virus (BIV) induced syncytium formation and BIV long terminal repeat (LTR) directed luciferase (Luc) gene expression were applied to screen and evaluate anti AIDS drugs. Frequency of the syncytium formation and BIV LTR directed Luc activity were in proportion to the number of input BIV infected cells. AZT inhibited the syncytium formation and the BIV LTR directed Luc gene expression level. Its inhibitory effects were dosedependent with the IC 50 being 0.24 and 0.052 mmol / L, respectively.

Involvement of chromatin and histone acetylation in the regulation of HIV-LTR by thyroid hormone receptor

The HIV-1 LTR controls the expression of HIV-1 viral genes and thus is critical for viral propagation and pathology. Numerous host factors have been shown to participate in the regulation of the LTR promoter. Among them is the thyroid hormone (T3) receptor (TR). TR has been shown to bind to the critical region of the promoter that contain the NFbB and Sp1 binding sites. Interestingly, earlier transient transfection studies in tissue culture cells have yielded contradicting conclusions on the role of TR in LTR regulation, likely due to the use of different cell types and/or lack of proper chromatin organization. Here, using the frog oocyte as a model system that allows replication-coupled chromatin assembly, mimicking that in somatic cells, we demonstrate that unliganded heterodimers of TR and RXR (9-cis retinoic acid receptor) repress LTR while the addition of T3 relieves the repression and further activates the promoter. More importantly, we show that chromatin and unliganded TR/RXR synergize to repress the promoter in a histone deacetylase-dependent manner.

Genomic Rearrangement in Endogenous Long Terminal Repeat Retrotransposons of Rice Lines Introgressed by Wild Rice （Zizania latifolia Griseb.）

Stochastic introgression of alien DNA may impose a genomic stress to the recipient genome. Herein, we report that apparent de novo genomic rearrangements in 10 of 13 selected endogenous, lowcopy, and potentially active long terminal repeat （LTR） retrotransposons occurred in one or more of three rice lines studied that were introgressed by wild rice （Zizania latifolia Griseb.）. For nine retrotransposons in which both the reverse-transcriptase （RT） region and the LTR region were available, largely concordant rearrangements occurred at both regions in five elements and at the RT region only in the remaining four elements. A marked proportion of the genomic changes was shared by two or all three introgression lines that were derived from a single F~ plant. This indicates that most of the genomic changes occurred at early developmental stages of the F~ somatic cells, which then gave rise to germline cells, and, hence, ensured inheritance of the changes to later generations. Possible causes and potential implications of the introgression-induced genomic rearrangements in LTR retrotransposons are discussed in the context of plant genome evolution and breeding.

M2 pyruvate kinase enhances HIV-1 transcription from its long terminal repeat

Both thymocytes and tumor cells express M2 type isoenzyme of pyruvate kinase(M2PK),which is different from R type isoenzyme of pyruvate kinase(RPK)that is expressed in erythrocytes.In this report,the effect of RPK and M2PK on the transcription of human immunodeficiency virus type 1(HIV-1)was tested.The results indicated that M2PK could enhance HIV-1 transcription from its long terminal repeat(LTR)promoter,while RPK did not have such an effect.Specific down-regulation of M2PK could inhibit HIV-1 transcription from its LTR region.Furthermore,it was found that the C terminal region of M2PK is responsible for this effect.Collectively,the cellular factor M2PK that is expressed in thymocytes could facilitate the transcription of HIV-1.

Intracellular CMTM2 negatively regulates human immunodeficiency virus type-1 transcription through targeting the transcription factors AP-1 and CREB

Background The CKLF-like MARVEL transmembrane domain-containing family （CMTM） is a novel family of proteins linking chemokines and TM4SF. Different members exhibit diverse biological functions. In this study, the effect of intracellular CMTM2 on regulating human immunodeficiency virus type-1 （HIV-1） transcription was evaluated.Methods The effects of CMTM2 on regulating full-length HIV-1 provirus and the HIV-1 long terminal repeat （LTR）-directed transcription were assessed by luciferase assay. Transcription factor assays, using the luciferase reporter plasmids of AP-1, CRE, and NF-κB were conducted to explore the signaling pathway（s） that may be regulated by CMTM2. The potential relationship between CMTM2 and the transcription factor AP-1 was further analyzed by Western blotting analyses to investigate the effect of CMTM2 on PMA-induced ERK1/2 phosphorylation.Results The results from the current study revealed that CMTM2 acts as a negative regulator of HIV-1 transcription.CMTM2 exerted a suppressive action on both full-length HIV-1 provirus and HIV-1 LTR-directed transcription.Transcription factor assays showed that CMTM2 selectively inhibited basal AP-1 and CREB activity. Co-expression of HIV-1 Tat, a potent AP-1 and CREB activator, can not reverse CMTM2-mediated AP-1 and CREB inhibition, suggesting a potent and specific effect of CMTM2 on negatively regulating these two signaling pathways.Conclusion Intracellular CMTM2 can negatively regulate HIV-1 transcription, at least in part, by targeting the AP-1 and CREB pathways. Exploring the mechanisms further may lead to new ways to control HIV-1 replication.

Cultivated hawthorn(Crataegus pinnatifida var.major)genome sheds light on the evolution of Maleae(apple tribe)

Cultivated hawthorn(Crataegus pinnatifida var.major)is an important medicinal and edible plant with a long history of use for health protection in China.Herein,we provide a de novo chromosomelevel genome sequence of the hawthorn cultivar“Qiu Jinxing.”We assembled an 823.41 Mb genome encoding 40571 genes and further anchored the779.24 Mb sequence into 17 pseudo-chromosomes,which account for 94.64%of the assembled genome.Phylogenomic analyses revealed that cultivated hawthorn diverged from other species within the Maleae(apple tribe)at approximately 35.4 Mya.Notably,genes involved in the flavonoid and triterpenoid biosynthetic pathways have been significantly amplified in the hawthorn genome.In addition,our results indicated that the Maleae share a unique ancient tetraploidization event;however,no recent independent whole-genome duplication event was specifically detected in hawthorn.The amplification of non-specific long terminal repeat retrotransposons contributed the most to the expansion of the hawthorn genome.Furthermore,we identified two paleo-sub-genomes in extant species of Maleae and found that these two sub-genomes showed different rearrangement mechanisms.We also reconstructed the ancestral chromosomes of Rosaceae and discussed two possible paleopolyploid origin patterns(autopolyploidization or allopolyploidization)of Maleae.Overall,our study provides an improved context for understanding the evolution of Maleae species,and this new highquality reference genome provides a useful resource for the horticultural improvement of hawthorn.

The CREB Regulated Transcription Coactivator 2 Suppresses HIV-1 Transcription by Preventing RNA PolⅡfrom Binding to HIV-1 LTR

The CREB-regulated transcriptional co-activators(CRTCs),including CRTC1,CRTC2 and CRTC3,enhance transcription of CREB-targeted genes.In addition to regulating host gene expression in response to cAMP,CRTCs also increase the infection of several viruses.While human immunodeficiency virus type 1(HIV-1)long terminal repeat(LTR)promoter harbors a cAMP response element and activation of the cAMP pathway promotes HIV-1 transcription,it remains unknown whether CRTCs have any effect on HIV-1 transcription and HIV-1 infection.Here,we reported that CRTC2 expression was induced by HIV-1 infection,but CRTC2 suppressed HIV-1 infection and diminished viral RNA expression.Mechanistic studies revealed that CRTC2 inhibited transcription from HIV-1 LTR and diminished RNA PolⅡoccupancy at the LTR independent of its association with CREB.Importantly,CRTC2 inhibits the activation of latent HIV-1.Together,these data suggest that in response to HIV-1 infection,cells increase the expression of CRTC2 which inhibits HIV-1 gene expression and may play a role in driving HIV-1 into latency.