Ontogeny and function of the circadian clock in intestinal organoids.

Circadian rhythms regulate diverse aspects of gastrointestinal physiology ranging from the composition of microbiota to motility. However, development of the intestinal circadian clock and detailed mechanisms regulating circadian physiology of the intestine remain largely unknown. In this report, we show that both pluripotent stem cell-derived human intestinal organoids engrafted into mice and patient-derived human intestinal enteroids possess circadian rhythms and demonstrate circadian phase-dependent necrotic cell death responses to Clostridium difficile toxin B (TcdB). Intriguingly, mouse and human enteroids demonstrate anti-phasic necrotic cell death responses to TcdB. RNA-Seq analysis shows that ~3-10% of the detectable transcripts are rhythmically expressed in mouse and human enteroids. Remarkably, we observe anti-phasic gene expression of Rac1, a small GTPase directly inactivated by TcdB, between mouse and human enteroids, and disruption of Rac1 abolishes clock-dependent necrotic cell death responses. Our findings uncover robust functions of circadian rhythms regulating clock-controlled genes in both mouse and human enteroids governing organism-specific, circadian phase-dependent necrotic cell death responses, and lay a foundation for human organ- and disease-specific investigation of clock functions using human organoids for translational applications.

Regulation of estrogen receptor alpha by the SET7 lysine methyltransferase.

Estrogen receptor alpha (ER) is a ligand-dependent transcription factor. Upon binding estrogen, ER recruits coactivator complexes with histone acetyltransferase or methyltransferase activities to activate downstream target genes. In addition to histones, coactivators can modify ER itself and other proteins in the transactivation complex. Here, we show that ER is directly methylated at lysine 302 (K302) by the SET7 methyltransferase. SET7-mediated methylation stabilizes ER and is necessary for the efficient recruitment of ER to its target genes and for their transactivation. The SET7-ER complex structure reveals the molecular basis for ER peptide recognition and predicts that modifications or mutations of nearby residues would affect K302 methylation. Indeed, a breast cancer-associated mutation at K303 (K303R) alters methylation at K302 in vitro and in vivo. These findings raise the possibility that generation, recognition, and removal of modifications within the ER hinge region generate "ER modification cassettes" that yield distinct patterns for signaling downstream events.

Landscape of genomic structural variations in Indian population-based cohorts: Deeper insights into their prevalence and clinical relevance.

Structural variations (SV) are large (>50 base pairs) genomic rearrangements comprising deletions, duplications, insertions, inversions, and translocations. Studying SVs is important because they play active and critical roles in regulating gene expression, determining disease predispositions, and identifying population-specific differences among individuals of diverse ancestries. However, SV discoveries in the Indian population using whole-genome sequencing (WGS) have been limited. In this study, using short-read WGS having an average 42X depth of coverage, we identify and characterize 36,210 SVs from 529 individuals enrolled in population-based cohorts in India. These SVs include 24,574 deletions, 2,913 duplications, 8,710 insertions, and 13 inversions; 1.26% (456 out of 36,210) of the identified SVs can potentially impact the coding regions of genes. Furthermore, 56 of these SVs are highly intolerant to loss-of-function changes to the mapped genes, and five SVs impacting ADAMTS17, CCDC40, and RHCE are common in our study individuals. Seven rare SVs significantly impact dosage sensitivity of genes known to be associated with various clinical phenotypes. Most of the SVs in our study are rare and heterozygous. This fine-scale SV discovery in the underrepresented Indian population provides valuable insights that extend beyond Eurocentric human genetic studies.

Broad de-regulated U2AF1 splicing is prognostic and augments leukemic transformation via protein arginine methyltransferase activation.

The role of splicing dysregulation in cancer is underscored by splicing factor mutations; however, its impact in the absence of such rare mutations is poorly understood. To reveal complex patient subtypes and putative regulators of pathogenic splicing in Acute Myeloid Leukemia (AML), we developed a new approach called OncoSplice. Among diverse new subtypes, OncoSplice identified a biphasic poor prognosis signature that partially phenocopies U2AF1-mutant splicing, impacting thousands of genes in over 40% of adult and pediatric AML cases. U2AF1-like splicing co-opted a healthy circadian splicing program, was stable over time and induced a leukemia stem cell (LSC) program. Pharmacological inhibition of the implicated U2AF1-like splicing regulator, PRMT5, rescued leukemia mis-splicing and inhibited leukemic cell growth. Genetic deletion of IRAK4, a common target of U2AF1-like and PRMT5 treated cells, blocked leukemia development in xenograft models and induced differentiation. These analyses reveal a new prognostic alternative-splicing mechanism in malignancy, independent of splicing-factor mutations.

Synthetic Gene Network with Positive Feedback Loop Amplifies Cellulase Gene Expression in Neurospora crassa.

Second-generation or lignocellulosic biofuels are a tangible source of renewable energy, which is critical to combat climate change by reducing the carbon footprint. Filamentous fungi secrete cellulose-degrading enzymes called cellulases, which are used for production of lignocellulosic biofuels. However, inefficient production of cellulases is a major obstacle for industrial-scale production of second-generation biofuels. We used computational simulations to design and implement synthetic positive feedback loops to increase gene expression of a key transcription factor, CLR-2, that activates a large number of cellulases in a filamentous fungus, Neurospora crassa. Overexpression of CLR-2 reveals previously unappreciated roles of CLR-2 in lignocellulosic gene network, which enabled simultaneous induction of approximately 50% of 78 lignocellulosic degradation-related genes in our engineered Neurospora strains. This engineering results in dramatically increased cellulase activity due to cooperative orchestration of multiple enzymes involved in the cellulose degradation pathway. Our work provides a proof of principle in utilizing mathematical modeling and synthetic biology to improve the efficiency of cellulase synthesis for second-generation biofuel production.

Infrequent mutation of ATBF1 in human breast cancer.

Deletion at chromosome 16q is frequent in prostate and breast cancers, suggesting the existence of one or more tumor suppressor genes in 16q. Recently, the transcription factor ATBF1 at 16q22 was identified as a strong candidate tumor suppressor gene in prostate cancer, and loss of ATBF1 expression was associated with poorer prognosis in breast cancer. In the present study, we examined mutation, expression, and promoter methylation of ATBF1 in 32 breast cancer cell lines. Only 2 of the 32 cancer cell lines had mutations, although 18 nucleotide polymorphisms were detected. In addition, 24 of 32 (75%) cancer cell lines had reduced ATBF1 mRNA levels, yet promoter methylation was not involved in gene silencing. These findings suggest that ATBF1 plays a role in breast cancer through transcriptional downregulation rather than mutations.

The enzymatic basis of processivity in lambda exonuclease.

Lambda exonuclease is a highly processive 5'-->3' exonuclease that degrades double-stranded (ds)DNA. The single-stranded DNA produced by lambda exonuclease is utilized by homologous pairing proteins to carry out homologous recombination. The extensive studies of lambda biology, lambda exonuclease enzymology and the availability of the X-ray crystallographic structure of lambda exonuclease make it a suitable model to dissect the mechanisms of processivity. lambda Exonuclease is a toroidal homotrimeric molecule and this quaternary structure is a recurring theme in proteins engaged in processive reactions in nucleic acid metabolism. We have identified residues in lambda exonuclease involved in recognizing the 5'-phosphate at the ends of broken dsDNA. The preference of lambda exonuclease for a phosphate moiety at 5' dsDNA ends has been established in previous studies; our results indicate that the low activity in the absence of the 5'-phosphate is due to the formation of inert enzyme-substrate complexes. By examining a lambda exonuclease mutant impaired in 5'-phosphate recognition, the significance of catalytic efficiency in modulating the processivity of lambda exonuclease has been elucidated. We propose a model in which processivity of lambda exonuclease is expressed as the net result of competition between pathways that either induce forward translocation or promote reverse translocation and dissociation.