To unwind the biological knots:The DNA/RNA G-quadruplex resolvase RHAU(DHX36)in development and disease

The G-quadruplex(G4)sequences are short fragments of 4-i nterval triple guanine(G)with frequent and ubiquitous distribution in the genome and RNA transcripts.The G4sequences are usually folded into secondary“knot”structure via Hoogsteen hydrogen bond to exert negative regulation on a variety of biological processes,including DNA replication and transcription,mRNA translation,and telomere maintenance.Recent structural biological and mouse genetics studies have demonstrated that RHAU(DHX36)can bind and unwind the G4“knots”to modulate embryonic development and postnatal organ function.Deficiency of RHAU gives rise to embryonic lethality,impaired organogenesis,and organ dysfunction.These studies uncovered the pivotal G4 resolvase function of RHAU to release the G4 barrier,which plays fundamental roles in development and physiological homeostasis.This review discusses the latest advancements and findings in deciphering RHAU functions using animal models.

LonP1 Links Mitochondria–ER Interaction to Regulate Heart Function

Interorganelle contacts and communications are increasingly recognized to play a vital role in cellular function and homeostasis.In particular,the mitochondria–endoplasmic reticulum(ER)membrane contact site(MAM)is known to regulate ion and lipid transfer,as well as signaling and organelle dynamics.However,the regulatory mechanisms of MAM formation and their function are still elusive.Here,we identify mitochondrial Lon protease(LonP1),a highly conserved mitochondrial matrix protease,as a new MAM tethering protein.The removal of LonP1 substantially reduces MAM formation and causes mitochondrial fragmentation.Furthermore,deletion of LonP1 in the cardiomyocytes of mouse heart impairs MAM integrity and mitochondrial fusion and activates the unfolded protein response within the ER(UPR^(ER)).Consequently,cardiac-specific LonP1 deficiency causes aberrant metabolic reprogramming and pathological heart remodeling.These findings demonstrate that LonP1 is a novel MAM-localized protein orchestrating MAM integrity,mitochondrial dynamics,and UPR^(ER),offering exciting new insights into the potential therapeutic strategy for heart failure.

Discovering small molecules as Wnt inhibitors that promote heart regeneration and injury repair

There are intense interests in discovering pro regenerative medicine leads that can promote cardiac differentiation and regeneration,as well as repair damaged heart tissues.We have combined zebrafish embryo-based screens with cardiomyogenesis assays to discover selective small molecules that modulate heart development and regeneration with minimal adverse effects.Two related compounds with novel structures,named as Cardiomogen 1 and 2(CDMG1 and CDMG2),were identified for their capacity to promote myocardial hyperplasia through expansion of the cardiac progenitor cell population.We find that Cardiomogen acts as a Wnt inhibitor by targeting p-catenin and reducing Tcf/Lef-mediated transcription in cultured cells.CDMG treatment of amputated zebrafish hearts reduces nuclear p-catenin in injured heart tissue,increases cardiomyocyte(CM)proliferation,and expedites wound healing,thus accelerating cardiac muscle regeneration.Importantly,Cardiomogen can alleviate the functional deterioration of mammalian hearts after myocardial infarction.Injured hearts exposed to CDMG1 display increased newly formed CMs and reduced fibrotic scar tissue,which are in part attributable to the^-catenin reduction.Our findings indicate Cardiomogen as a Wnt inhibitor in enhancing injury-induced CM proliferation and heart regeneration,highlighting the values of embryo-based small molecule screens in discovery of effective and safe medicine leads.

TSC1 controls IL-1β expression in macrophages via mTORCl-dependent C/EBPβ pathway

The tuberous sclerosis complex I （TSC1） is a tumor suppressor that inhibits the mammalian target of rapamycin （mTOR）, which serves as a key regulator of inflammatory responses after bacterial stimulation in monocytes, macrophages, and primary dendritic cells. Previous studies have shown that TSC1 knockout （KO） macrophages produced increased inflammatory responses including tumor necrosis factor-a （TNF-a） and IL-12 to pro-inflammatory stimuli, but whether and how TSC1 regulates pro-lL-lJ~ expression remains unclear. Here using a mouse model in which myeloid lineage-specific deletion of TSC1 leads to constitutive mTORC1 activation, we found that TSC1 deficiency resulted in impaired expression of pro-I L-1β in macrophages following l ipopolysaccharide stimulation. Such decreased pro-I L-1β expression in TSC1 KO macrophages was rescued by reducing mTORC1 activity with rapamycin or deletion of mTOR. Rictor deficiency has no detectable effect on pro-lL-1β synthesis, suggesting that TSC1 positively controls pro-1L-1β expression through mTORC 1 pathway. Moreover, mechanism studies suggest that mTORC 1-mediated downregulation of the CCAAT enhancer-binding protein （C/EBPβ） critically contributes to the defective pro-lL-1β expression. Overall, these findings highlight a critical role of TSC1 in regulating innate immunity by control of the mTOR1-C/EBPβ pathway.

GATA2^(−/−) human ESCs undergo attenuatedendothelial to hematopoietic transition andthereafter granulocyte commitment

Background: Hematopoiesis is a progressive process collectively controlled by an elaborate network of transcriptionfactors (TFs). Among these TFs, GATA2 has been implicated to be critical for regulating multiple steps of hematopoiesisin mouse models. However, whether similar function of GATA2 is conserved in human hematopoiesis, especially duringearly embryonic development stage, is largely unknown.Results: To examine the role of GATA2 in human background, we generated homozygous GATA2 knockout humanembryonic stem cells (GATA2^(−/−) hESCs) and analyzed their blood differentiation potential. Our results demonstratedthat GATA2^(−/−) hESCs displayed attenuated generation of CD34^(+)CD43^(+) hematopoietic progenitor cells (HPCs), due tothe impairment of endothelial to hematopoietic transition (EHT). Interestingly, GATA2^(−/−) hESCs retained the potentialto generate erythroblasts and macrophages, but never granulocytes. We further identified that SPI1 downregulationwas partially responsible for the defects of GATA2^(−/−) hESCs in generation of CD34^(+)CD43^(+) HPCs and granulocytes.Furthermore, we found that GATA2^(−/−) hESCs restored the granulocyte potential in the presence of Notch signaling.Conclusion: Our findings revealed the essential roles of GATA2 in EHT and granulocyte development throughregulating SPI1, and uncovered a role of Notch signaling in granulocyte generation during hematopoiesis modeled byhuman ESCs.

Master microRNA-222 regulates cardiac microRNA maturation and triggers Tetralogy of Fallot

Dear Editor,Tetralogy of Fallot(TOF)is the most common complex congenital heart disease.Besides gene mutations and copy number variants,altered protein function induced by posttranscriptional or translational regulation also contributes to the onset of TOF.1 MiRNAs are short noncoding RNAs that bind to the 3’-UTR of target mRNAs to repress protein production.However,the causal link between miRNAs and TOF and the underlying mechanism has not been established.