For more papers, visit a faculty member's page from the listing on Whitehead Faculty and access the PubMed link.
Inhibition of hypothalamic MCT1 expression increases food intake and alters orexigenic and anorexigenic neuropeptide expression.
Sci Rep. 2016 Sep 28;6:33606.
Elizondo-Vega, R., Cortes-Campos, C.*, Barahona, M.J., Carril, C., Ordenes, P., Salgado, M., Oyarce, K., and Garcia-Robles, M.L.
Hypothalamic glucosensing, which involves the detection of glucose concentration changes by brain cells and subsequent release of orexigenic or anorexigenic neuropeptides, is a crucial process that regulates feeding behavior. Arcuate nucleus (AN) neurons are classically thought to be responsible for hypothalamic glucosensing through a direct sensing mechanism; however, recent data has shown a metabolic interaction between tanycytes and AN neurons through lactate that may also be contributing to this process. Monocarboxylate transporter 1 (MCT1) is the main isoform expressed by tanycytes, which could facilitate lactate release to hypothalamic AN neurons. We hypothesize that MCT1 inhibition could alter the metabolic coupling between tanycytes and AN neurons, altering feeding behavior. To test this, we inhibited MCT1 expression using adenovirus-mediated transfection of a shRNA into the third ventricle, transducing ependymal wall cells and tanycytes. Neuropeptide expression and feeding behavior were measured in MCT1-inhibited animals after intracerebroventricular glucose administration following a fasting period. Results showed a loss in glucose regulation of orexigenic neuropeptides and an abnormal expression of anorexigenic neuropeptides in response to fasting. This was accompanied by an increase in food intake and in body weight gain. Taken together, these results indicate that MCT1 expression in tanycytes plays a role in feeding behavior regulation.
Prodigious plant methylomes.
Genome Biol. 2016 Sep 27;17(1):197.
Schmitz and colleagues recently investigated DNA methylation patterns in diverse flowering plant species, finding substantial variation in the extent and distribution of methylation in angiosperms.
O-fucosylated glycoproteins form assemblies in close proximity to the nuclear pore complexes of Toxoplasma gondii.
Proc Natl Acad Sci U S A. 2016 Sep 23.
Bandini, G., Haserick, J.R., Motari, E., Ouologuem, D.T., Lourido, S.*, Roos, D.S., Costello, C.E., Robbins, P.W., and Samuelson, J.
Toxoplasma gondii is an intracellular parasite that causes disseminated infections in fetuses and immunocompromised individuals. Although gene regulation is important for parasite differentiation and pathogenesis, little is known about protein organization in the nucleus. Here we show that the fucose-binding Aleuria aurantia lectin (AAL) binds to numerous punctate structures in the nuclei of tachyzoites, bradyzoites, and sporozoites but not oocysts. AAL also binds to Hammondia and Neospora nuclei but not to more distantly related apicomplexans. Analyses of the AAL-enriched fraction indicate that AAL binds O-linked fucose added to Ser/Thr residues present in or adjacent to Ser-rich domains (SRDs). Sixty-nine Ser-rich proteins were reproducibly enriched with AAL, including nucleoporins, mRNA-processing enzymes, and cell-signaling proteins. Two endogenous SRDs-containing proteins and an SRD-YFP fusion localize with AAL to the nuclear membrane. Superresolution microscopy showed that the majority of the AAL signal localizes in proximity to nuclear pore complexes. Host cells modify secreted proteins with O-fucose; here we describe the O-fucosylation pathway in the nucleocytosol of a eukaryote. Furthermore, these results suggest O-fucosylation is a mechanism by which proteins involved in gene expression accumulate near the NPC.
Editing DNA methylation in the mammalian genome.
Cell. 2016 Sep 22;167(1):233-247
Liu, X.S.*, Wu, H.*, Ji, X.*, Stelzer, Y.*, Wu, X.*, Czauderna, S.*, Shu, J.*, Dadon, D.*, Young, R.A.*, and Jaenisch, R.*
Mammalian DNA methylation is a critical epigenetic mechanism orchestrating gene expression networks in many biological processes. However, investigation of the functions of specific methylation events remains challenging. Here, we demonstrate that fusion of Tet1 or Dnmt3a with a catalytically inactive Cas9 (dCas9) enables targeted DNA methylation editing. Targeting of the dCas9-Tet1 or -Dnmt3a fusion protein to methylated or unmethylated promoter sequences caused activation or silencing, respectively, of an endogenous reporter. Targeted demethylation of the BDNF promoter IV or the MyoD distal enhancer by dCas9-Tet1 induced BDNF expression in post-mitotic neurons or activated MyoD facilitating reprogramming of fibroblasts into myoblasts, respectively. Targeted de novo methylation of a CTCF loop anchor site by dCas9-Dnmt3a blocked CTCF binding and interfered with DNA looping, causing altered gene expression in the neighboring loop. Finally, we show that these tools can edit DNA methylation in mice, demonstrating their wide utility for functional studies of epigenetic regulation.
The Simons Genome Diversity Project: 300 genomes from 142 diverse populations.
Nature. 2016 Sep 21.
Mallick, S., Li, H., Lipson, M., Mathieson, I., Gymrek, M.*, Racimo, F., Zhao, M., Chennagiri, N., Nordenfelt, S., Tandon, A., Skoglund, P., Lazaridis, I., Sankararaman, S., Fu, Q., Rohland, N., Renaud, G., Erlich ,Y., Willems, T., Gallo, C., Spence, J.P., Song, Y.S., Poletti, G., Balloux, F., van Driem, G., de Knijff, P., Romero, I.G., Jha, A.R., Behar, D.M., Bravi, C.M., Capelli, C., Hervig, T., Moreno-Estrada, A., Posukh, O.L., Balanovska, E., Balanovsky, O., Karachanak-Yankova, S., Sahakyan, H., Toncheva, D., Yepiskoposyan, L., Tyler-Smith, C., Xue, Y., Abdullah, M.S., Ruiz-Linares, A., Beall, C.M., Di Rienzo, A., Jeong, C., Starikovskaya, E.B., Metspalu, E., Parik, J., Villems, R., Henn, B.M., Hodoglugil, U., Mahley, R., Sajantila, A., Stamatoyannopoulos, G., Wee, J.T., Khusainova, R., Khusnutdinova, E., Litvinov, S., Ayodo, G., Comas, D., Hammer, M.F., Kivisild, T., Klitz, W., Winkler, C.A., Labuda, D., Bamshad, M., Jorde, L.B., Tishkoff, S.A., Watkins, W.S., Metspalu, M., Dryomov, S., Sukernik, R., Singh, L., Thangaraj, K., Pääbo, S., Kelso, J., Patterson, N., and Reich, D.
Here we report the Simons Genome Diversity Project data set: high quality genomes from 300 individuals from 142 diverse populations. These genomes include at least 5.8 million base pairs that are not present in the human reference genome. Our analysis reveals key features of the landscape of human genome variation, including that the rate of accumulation of mutations has accelerated by about 5% in non-Africans compared to Africans since divergence. We show that the ancestors of some pairs of present-day human populations were substantially separated by 100,000 years ago, well before the archaeologically attested onset of behavioural modernity. We also demonstrate that indigenous Australians, New Guineans and Andamanese do not derive substantial ancestry from an early dispersal of modern humans; instead, their modern human ancestry is consistent with coming from the same source as that of other non-Africans.
Parent-of-origin DNA methylation dynamics during mouse development.
Cell Rep. 2016 Sep 20;16(12):3167-80.
Stelzer, Y.*, Wu, H.*, Song, Y.*, Shivalila, C.S.*, Markoulaki, S.*, and Jaenisch, R.*
Parent-specific differentially methylated regions (DMRs) are established during gametogenesis and regulate parent-specific expression of imprinted genes. Monoallelic expression of imprinted genes is essential for development, suggesting that imprints are faithfully maintained in embryos and adults. To test this hypothesis, we targeted a reporter for genomic methylation to the imprinted Dlk1-Dio3 intergenic DMR (IG-DMR) to assess the methylation of both parental alleles at single-cell resolution. Biallelic gain or loss of IG-DMR methylation occurred in a small fraction of mouse embryonic stem cells, significantly affecting developmental potency. Mice carrying the reporter in either parental allele showed striking parent-specific changes in IG-DMR methylation, causing substantial and consistent tissue- and cell-type-dependent signatures in embryos and postnatal animals. Furthermore, dynamics in DNA methylation persisted during adult neurogenesis, resulting in inter-individual diversity. This substantial cell-cell DNA methylation heterogeneity implies that dynamic DNA methylation variations in the adult may be of functional importance.
Germinal center B cell dynamics.
Immunity. 2016 Sep 20;45(3):471-82.
Mesin, L.*, Ersching, J.*, and Victora, G.D.*
Germinal centers (GCs) are the site of antibody diversification and affinity maturation and as such are vitally important for humoral immunity. The study of GC biology has undergone a renaissance in the past 10 years, with a succession of findings that have transformed our understanding of the cellular dynamics of affinity maturation. In this review, we discuss recent developments in the field, with special emphasis on how GC cellular and clonal dynamics shape antibody affinity and diversity during the immune response.
The apo-structure of the leucine sensor Sestrin2 is still elusive.
Sci Signal. 2016 Sep 20;9(446):ra92.
Saxton, R.A.*, Knockenhauer, K.E., Schwartz, T.U., and Sabatini, D.M.*
9, ra92.Sestrin2 is a GATOR2-interacting protein that directly binds leucine and is required for the inhibition of mTORC1 under leucine deprivation, indicating that it is a leucine sensor for the mTORC1 pathway. We recently reported the structure of Sestrin2 in complex with leucine [Protein Data Bank (PDB) ID, 5DJ4] and demonstrated that mutations in the leucine-binding pocket that alter the affinity of Sestrin2 for leucine result in a corresponding change in the leucine sensitivity of mTORC1 in cells. A lower resolution structure of human Sestrin2 (PDB ID, 5CUF), which was crystallized in the absence of exogenous leucine, showed Sestrin2 to be in a nearly identical conformation as the leucine-bound structure. On the basis of this observation, it has been argued that leucine binding does not affect the conformation of Sestrin2 and that Sestrin2 may not be a sensor for leucine. We show that simple analysis of the reported "apo"-Sestrin2 structure reveals the clear presence of prominent, unmodeled electron density in the leucine-binding pocket that exactly accommodates the leucine observed in the higher resolution structure. Refining the reported apo-structure with leucine eliminated the large Fobs-Fcalc difference density at this position and improved the working and free R factors of the model. Consistent with this result, our own structure of Sestrin2 crystallized in the absence of exogenous leucine also contained electron density that is best explained by leucine. Thus, the structure of apo-Sestrin2 remains elusive.
Conserved imprinting associated with unique epigenetic signatures in the i genus.
Nat Plants. 2016 Sep 19;2:16145.
Klosinska, M.*, Picard, C.L.*, and Gehring, M.*
In plants, imprinted gene expression occurs in endosperm seed tissue and is sometimes associated with differential DNA methylation between maternal and paternal alleles1. Imprinting is theorized to have been selected for because of conflict between parental genomes in offspring2, but most studies of imprinting have been conducted in Arabidopsis thaliana, an inbred primarily self-fertilizing species that should have limited parental conflict. We examined embryo and endosperm allele-specific expression and DNA methylation genome-wide in the wild outcrossing species Arabidopsis lyrata. Here we show that the majority of A. lyrata imprinted genes also exhibit parentally biased expression in A. thaliana, suggesting that there is evolutionary conservation in gene imprinting. Surprisingly, we discovered substantial interspecies differences in methylation features associated with paternally expressed imprinted genes (PEGs). Unlike in A. thaliana, the maternal allele of many A. lyrata PEGs was hypermethylated in the CHG context. Increased maternal allele CHG methylation was associated with increased expression bias in favour of the paternal allele. We propose that CHG methylation maintains or reinforces repression of maternal alleles of PEGs. These data suggest that the genes subject to imprinting are largely conserved, but there is flexibility in the epigenetic mechanisms employed between closely related species to maintain monoallelic expression. This supports the idea that imprinting of specific genes is a functional phenomenon, and not simply a byproduct of seed epigenomic reprogramming.
Modeling disease risk through analysis of physical interactions between genetic variants within chromatin regulatory circuitry.
Nat Genet. 2016 Sep 19.
Corradin, O.*, Cohen, A.J., Luppino, J.M., Bayles, I.M., Schumacher, F.R., and Scacheri, P.C.
SNPs associated with disease susceptibility often reside in enhancer clusters, or super-enhancers. Constituents of these enhancer clusters cooperate to regulate target genes and often extend beyond the linkage disequilibrium (LD) blocks containing risk SNPs identified in genome-wide association studies (GWAS). We identified 'outside variants', defined as SNPs in weak LD with GWAS risk SNPs that physically interact with risk SNPs as part of a target gene's regulatory circuitry. These outside variants further explain variation in target gene expression beyond that explained by GWAS-associated SNPs. Additionally, the clinical risk associated with GWAS SNPs is considerably modified by the genotype of outside variants. Collectively, these findings suggest a potential model in which outside variants and GWAS SNPs that physically interact in 3D chromatin collude to influence target transcript levels as well as clinical risk. This model offers an additional hypothesis for the source of missing heritability for complex traits.
*Author affiliated with Whitehead Institute for Biomedical Research