Eukaryotic Pif1 helicase unwinds G-quadruplex and dsDNA using a conserved wedge.

G-quadruplexes (G4s) formed by guanine-rich nucleic acids induce genome instability through impeding DNA replication fork progression. G4s are stable DNA structures, the unfolding of which require the functions of DNA helicases. Pif1 helicase binds preferentially to G4 DNA and plays multiple roles in maintaining genome stability, but the mechanism by which Pif1 unfolds G4s is poorly understood. Here we report the co-crystal structure of Saccharomyces cerevisiae Pif1 (ScPif1) bound to a G4 DNA with a 5' single-stranded DNA (ssDNA) segment. Unlike the Thermus oshimai Pif1-G4 structure, in which the 1B and 2B domains confer G4 recognition, ScPif1 recognizes G4 mainly through the wedge region in the 1A domain that contacts the 5' most G-tetrad directly. A conserved Arg residue in the wedge is required for Okazaki fragment processing but not for mitochondrial function or for suppression of gross chromosomal rearrangements. Multiple substitutions at this position have similar effects on resolution of DNA duplexes and G4s, suggesting that ScPif1 may use the same wedge to unwind G4 and dsDNA. Our results reveal the mechanism governing dsDNA unwinding and G4 unfolding by ScPif1 helicase that can potentially be generalized to other eukaryotic Pif1 helicases and beyond.

Activity-dependent compartmentalization of dendritic mitochondria morphology through local regulation of fusion-fission balance in neurons in vivo.

Neuronal mitochondria play important roles beyond ATP generation, including Ca2+ uptake, and therefore have instructive roles in synaptic function and neuronal response properties. Mitochondrial morphology differs significantly between the axon and dendrites of a given neuronal subtype, but in CA1 pyramidal neurons (PNs) of the hippocampus, mitochondria within the dendritic arbor also display a remarkable degree of subcellular, layer-specific compartmentalization. In the dendrites of these neurons, mitochondria morphology ranges from highly fused and elongated in the apical tuft, to more fragmented in the apical oblique and basal dendritic compartments, and thus occupy a smaller fraction of dendritic volume than in the apical tuft. However, the molecular mechanisms underlying this striking degree of subcellular compartmentalization of mitochondria morphology are unknown, precluding the assessment of its impact on neuronal function. Here, we demonstrate that this compartment-specific morphology of dendritic mitochondria requires activity-dependent, Ca2+ and Camkk2-dependent activation of AMPK and its ability to phosphorylate two direct effectors: the pro-fission Drp1 receptor Mff and the recently identified anti-fusion, Opa1-inhibiting protein, Mtfr1l. Our study uncovers a signaling pathway underlying the subcellular compartmentalization of mitochondrial morphology in dendrites of neurons in vivo through spatially precise and activity-dependent regulation of mitochondria fission/fusion balance.

Rare SNP in the HELB gene interferes with RPA interaction and cellular function of HELB.

HELB is a human helicase involved in initiation of DNA replication, the replication stress response, and regulation of double-strand DNA break repair. rs75770066 is a rare SNP in the HELB gene that affects age at natural menopause. rs75770066 results in a D506G substitution in an acidic patch within the 1A domain of the helicase that is known to interact with RPA. We found that this amino acid change dramatically impairs the cellular function of HELB. D506G-HELB exhibits impaired interaction with RPA, which likely results in the effects of rs75770066 as this reduces recruitment of HELB to sites of DNA damage. Reduced recruitment of D506G-HELB to double-strand DNA breaks and the concomitant increase in homologous recombination likely alters the levels of meiotic recombination, which affects the viability of gametes. Because menopause occurs when oocyte levels drop below a minimum threshold, altered repair of meiotic double-stranded DNA breaks has the potential to directly affect the age at natural menopause.

Diverse pathogen-associated molecular patterns affect transcription of genes in the toll-like receptor signaling pathway in goat blood.

Pathogen-associated molecular patterns (PAMPs) such as lipopolysaccharide (LPS), peptidoglycan (PGN), Polyinosinic-polycytidylic acid (poly I:C), and CpG Oligodeoxynucleotides (ODN) are recognized by Toll-like receptors (TLR). This study aimed to investigate the effect of diverse PAMPs on the transcription of TLR signaling pathway genes in goat blood. Whole blood was collected from 3 female BoerXSpanish goats and treated with the following PAMPs: 10 µg/ml LPS, PGN, CpG ODN (2216), CpG ODN (2006), and 12.5 µg/ml Poly I:C. Blood-treated PBS served as a control. The expression of 84 genes in the human TLR signaling pathway RT2 PCR Array (Qiagen) was evaluated using real-time PCR. Treatment with PBS affected the expression of 74 genes, Poly I:C affected the expression of 40 genes, t ODN 2006 affected the expression of 50 genes, ODN 2216 affected the expression of 52 genes, LPS affected the expression of 49 genes, while PGN affected the expression of 49 genes. Our results show that PAMPs modulated and increased the expression of genes in the TLR signaling pathway. These results highlight important insights into how the host responds to different pathogens and may help design adjuvants for therapeutics and vaccines that target different.

Activity-dependent subcellular compartmentalization of dendritic mitochondria structure in CA1 pyramidal neurons.

Neuronal mitochondria play important roles beyond ATP generation, including Ca2+ uptake, and therefore have instructive roles in synaptic function and neuronal response properties. Mitochondrial morphology differs significantly in the axon and dendrites of a given neuronal subtype, but in CA1 pyramidal neurons (PNs) of the hippocampus, mitochondria within the dendritic arbor also display a remarkable degree of subcellular, layer-specific compartmentalization. In the dendrites of these neurons, mitochondria morphology ranges from highly fused and elongated in the apical tuft, to more fragmented in the apical oblique and basal dendritic compartments, and thus occupy a smaller fraction of dendritic volume than in the apical tuft. However, the molecular mechanisms underlying this striking degree of subcellular compartmentalization of mitochondria morphology are unknown, precluding the assessment of its impact on neuronal function. Here, we demonstrate that this compartment-specific morphology of dendritic mitochondria requires activity-dependent, Camkk2-dependent activation of AMPK and its ability to phosphorylate two direct effectors: the pro-fission Drp1 receptor Mff and the recently identified anti-fusion, Opa1-inhibiting protein, Mtfr1l. Our study uncovers a new activity-dependent molecular mechanism underlying the extreme subcellular compartmentalization of mitochondrial morphology in dendrites of neurons in vivo through spatially precise regulation of mitochondria fission/fusion balance.

Neuronal mitochondrial morphology is significantly affected by both fixative and oxygen level during perfusion.

Neurons in the brain have a uniquely polarized structure consisting of multiple dendrites and a single axon generated from a cell body. Interestingly, intracellular mitochondria also show strikingly polarized morphologies along the dendrites and axons: in cortical pyramidal neurons (PNs), dendritic mitochondria have a long and tubular shape, while axonal mitochondria are small and circular. Mitochondria play important roles in each compartment of the neuron by generating adenosine triphosphate (ATP) and buffering calcium, thereby affecting synaptic transmission and neuronal development. In addition, mitochondrial shape, and thereby function, is dynamically altered by environmental stressors such as oxidative stress or in various neurodegenerative diseases including Alzheimer's disease and Parkinson's disease. Although the importance of altered mitochondrial shape has been claimed by multiple studies, methods for studying this stress-sensitive organelle have not been standardized. Here we address pertinent steps that influence mitochondrial morphology during experimental processes. We demonstrate that fixative solutions containing only paraformaldehyde (PFA), or that introduce hypoxic conditions during the procedure, induce dramatic fragmentation of mitochondria both in vitro and in vivo. This disruption was not observed following the use of glutaraldehyde (GA) addition or oxygen supplementation, respectively. Finally, using pre-formed fibril α-synuclein treated neurons, we show fixative choice can alter experimental outcomes. Specifically, α-synuclein-induced mitochondrial remodeling could not be observed with PFA only fixation as fixation itself caused mitochondrial fragmentation. Our study provides optimized methods for examining mitochondrial morphology in neurons and demonstrates that fixation conditions are critical when investigating the underlying cellular mechanisms involving mitochondria in physiological and neurodegenerative disease models.

Natural and synthetic pathogen associated molecular patterns modulate galectin expression in cow blood.

Pathogen-associated Molecular Patterns (PAMPs) are highly conserved structural motifs that are recognized by Pathogen Recognition receptors (PRRs) to initiate immune responses. Infection by these pathogens and the immune response to PAMPS such as lipopolysaccharide (LPS), Peptidoglycan (PGN), bacterial oligodeoxynucleotides [CpG oligodeoxynucleotides 2006 (CpG ODN2006) and CpG oligodeoxynucleotides 2216 (CpG ODN2216)], and viral RNA Polyinosinic-Polycytidylic Acid (Poly I:C), are associated with infectious and metabolic diseases in animals impacting health and production. It is established that PAMPs mediate the production of cytokines by binding to PRRs such as Toll-like receptors (TLR) on immune cells. Galectins (Gal) are carbohydrate-binding proteins that when expressed play essential roles in the resolution of infectious and metabolic diseases. Thus it is important to determine if the expression of galectin gene (LGALS) and Gal secretion in blood are affected by exposure to LPS and PGN, PolyI:C and bacterial CpG ODNs. LPS increased transcription of LGALS4 and 12 (2.5 and 2.02 folds respectively) and decreased secretion of Gal 4 (p < 0.05). PGN increased transcription of LGALS-1, -2, -3, -4, -7, and -12 (3.0, 2.3, 2.0, 4.1, 3.3, and 2.4 folds respectively) and secretion of Gal-8 and Gal-9 (p < 0.05). Poly I:C tended to increase the transcription of LGALS1, LGALS4, and LGALS8 (1.78, 1.88, and 1.73 folds respectively). Secretion of Gal-1, -3, -8 and nine were significantly increased in treated samples compared to control (p < 0.05). CpG ODN2006 did not cause any significant fold changes in LGALS transcription (FC < 2) but increased secretion of Gal-1, and-3 (p < 0.05) in plasma compared to control. Gal-4 was however reduced in plasma (p < 0.05). CpG ODN2216 increased transcription of LGALS1 and LGALS3 (3.8 and 1.6 folds respectively), but reduced LGALS2, LGALS4, LGALS7, and LGALS12 (-1.9, -2.0, -2.0 and; -2.7 folds respectively). Secretion of Gal-2 and -3 in plasma was increased compared to control (p < 0.05). Gal-4 secretion was reduced in plasma (p < 0.05). The results demonstrate that PAMPs differentially modulate galectin transcription and translation of galectins in cow blood.