Maternal inheritance of mitochondrial DNA

Maternal inheritance of mitochondrial DNA (mtDNA) is generally observed in many eukaryotes. Sperm-derived paternal mitochondria and their mtDNA enter the oocyte cytoplasm upon fertilization and then normally disappear during early embryogenesis. However, the mechanism underlying this clearance of paternal mitochondria has remained largely unknown. Recently, we showed that autophagy is required for the elimination of paternal mitochondria in Caenorhabditis elegans embryos. Shortly after fertilization, autophagosomes are induced locally around the penetrated sperm components. These autophagosomes engulf paternal mitochondria, resulting in their lysosomal degradation during early embryogenesis. In autophagy-defective zygotes, paternal mitochondria and their genomes remain even in the larval stage. Therefore, maternal inheritance of mtDNA is accomplished by autophagic degradation of paternal mitochondria. We also found that another kind of sperm-derived structure, called the membranous organelle, is degraded by zygotic autophagy as well. We thus propose to term this allogeneic (nonself) organelle autophagy as allophagy.     

Connections Between Benthic Populations and Local Strandings of the Southern Bull Kelp Durvillaea Antarctica Along the Continental Coast of Chile1

Floating seaweeds are important dispersal vectors in marine ecosystems. However, the relationship between benthic populations and stranded seaweeds has received little attention. After detachment, a fraction of floating specimens returns to the shore, resulting in strandings that fluctuate in space and time. It has been hypothesized that the availability of stranded seaweeds is related to their benthic abundance on adjacent coasts. Using the large fucoid Durvillaea antarctica, we tested whether stranded biomasses are higher at sites with dense adjacent benthic populations. Benthic abundance of D. antarctica along the continental coast of Chile was estimated using three approximations: (i) availability of potentially suitable habitat (PSH), (ii) categorical visual abundance estimates in the field, and (iii) abundance measurements in the intertidal zone. Higher PSH for D. antarctica was observed between 31° S–32° S and 40° S–42° S than between 33° S and 39° S. Lowest benthic biomasses were estimated for the northern latitudes (31° S–32° S). Regression models showed that the association between stranded biomass and PSH was highest when only the extent of rocky shore 10 km to the south of each beach was included, suggesting relatively short-distance dispersal and asymmetrical transport of floating kelps, which is further supported by low proportions of rafts with Lepas spp. (indicator of rafting). The results indicate that stranded biomasses are mostly subsidized by nearby benthic populations, which can partly explain the low genetic connectivity among populations in the study region. Future studies should also incorporate other local factors (e.g., winds, currents, wave-exposure) that influence stranding dynamics.     

Effect of isolation methodology on stem cell properties and multilineage differentiation potential of human dental pulp stem cells

Dental pulp stem cells (DPSCs) are an attractive alternative mesenchymal stem cell (MSC) source because of their isolation simplicity compared with the more invasive methods associated with harvesting other MSC sources. However, the isolation method to be favored for obtaining DPSC cultures remains under discussion. This study compares the stem cell properties and multilineage differentiation potential of DPSCs obtained by the two most widely adapted isolation procedures. DPSCs were isolated either by enzymatic digestion of the pulp tissue (DPSC-EZ) or by the explant method (DPSC-OG), while keeping the culture media constant throughout all experiments and in both isolation methods. Assessment of the stem cell properties of DPSC-EZ and DPSC-OG showed no significant differences between the two groups with regard to proliferation rate and colony formation. Phenotype analysis indicated that DPSC-EZ and DPSC-OG were positive for CD29, CD44, CD90, CD105, CD117 and CD146 expression without any significant differences. The multilineage differentiation potential of both stem cell types was confirmed by using standard immuno(histo/cyto)chemical staining together with an in-depth ultrastructural analysis by means of transmission electron microscopy. Our results indicate that both DPSC-EZ and DPSC-OG could be successfully differentiated into adipogenic, chrondrogenic and osteogenic cell types, although the adipogenic differentiation of both stem cell populations was incomplete. The data suggest that both the enzymatic digestion and outgrowth method can be applied to obtain a suitable autologous DPSC resource for tissue replacement therapies of both bone and cartilage.     

RNA-Seq analyses reveal the order of tRNA processing events and the maturation of C/D box and CRISPR RNAs in the hyperthermophile Methanopyrus kandleri

The methanogenic archaeon Methanopyrus kandleri grows near the upper temperature limit for life. Genome analyses revealed strategies to adapt to these harsh conditions and elucidated a unique transfer RNA (tRNA) C-to-U editing mechanism at base 8 for 30 different tRNA species. Here, RNA-Seq deep sequencing methodology was combined with computational analyses to characterize the small RNome of this hyperthermophilic organism and to obtain insights into the RNA metabolism at extreme temperatures. A large number of 132 small RNAs were identified that guide RNA modifications, which are expected to stabilize structured RNA molecules. The C/D box guide RNAs were shown to exist as circular RNA molecules. In addition, clustered regularly interspaced short palindromic repeats RNA processing and potential regulatory RNAs were identified. Finally, the identification of tRNA precursors before and after the unique C8-to-U8 editing activity enabled the determination of the order of tRNA processing events with termini truncation preceding intron removal. This order of tRNA maturation follows the compartmentalized tRNA processing order found in Eukaryotes and suggests its conservation during evolution.     

Differential proliferation rates generate patterns of mechanical tension that orient tissue growth

Orientation of cell divisions is a key mechanism of tissue morphogenesis. In the growing Drosophila wing imaginal disc epithelium, most of the cell divisions in the central wing pouch are oriented along the proximal–distal (P–D) axis by the Dachsous‐Fat‐Dachs planar polarity pathway. However, cells at the periphery of the wing pouch instead tend to orient their divisions perpendicular to the P–D axis despite strong Dachs polarization. Here, we show that these circumferential divisions are oriented by circumferential mechanical forces that influence cell shapes and thus orient the mitotic spindle. We propose that this circumferential pattern of force is not generated locally by polarized constriction of individual epithelial cells. Instead, these forces emerge as a global tension pattern that appears to originate from differential rates of cell proliferation within the wing pouch. Accordingly, we show that localized overgrowth is sufficient to induce neighbouring cell stretching and reorientation of cell division. Our results suggest that patterned rates of cell proliferation can influence tissue mechanics and thus determine the orientation of cell divisions and tissue shape.     

Recent Developments in Optical Neuromodulation Technologies

The emergence of optogenetics technology facilitated widespread applications for interrogation of complex neural networks, such as activation of specific axonal pathways, previously found impossible with electrical stimulation. Consequently, within the short period of its application in neuroscience research, optogenetics has led to findings of significant importance both during normal brain function as well as in disease. Moreover, the optimization of optogenetics for in vivo studies has allowed the control of certain behavioral responses such as motility, reflex, and sensory responses, as well as more complex emotional and cognitive behaviors such as decision-making, reward seeking, and social behavior in freely moving animals. These studies have produced a wide variety of animal models that have resulted in fundamental findings and enhanced our understanding of the neural networks associated with behavior. The increasing number of opsins available for this technique enabled even broader regulation of neuronal activity. These advancements highlight the potential of this technique for future treatment of human diseases. Here, we provide an overview of the recent developments in the field of optogenetics technology that are relevant for a better understanding of several neuropsychiatric and neurodegenerative disorders and may pave the way for future therapeutic interventions.     

Molecular Dynamics Study of Intrinsic Stability in Six RNA Terminal Loop Motifs

Abstract

Single stranded RNA molecules can assume a wide range of tertiary structures beyond the canonical A-form double helix. Certain sequences, termed motifs, are more common than a random distribution would suggest. The existence of such motifs can be rationalized in structural terms. In this study, we have investigated the intrinsic structural stability of RNA terminal loop motifs using multiple MD simulations in explicit water. Representative loops were chosen from the major tetraloop motifs, including also the U-turn motif. Not all loops retain their folded starting structure, but lowering the temperature to 277 K, or adding adjacent base pairs from the stem to which the motif is attached, helps stabilizing the folded loop structure.     

Mapping FLS2 function to structure: LRRs, kinase and its working bits

The plasma membrane-localised FLAGELLIN SENSING 2 (FLS2) receptor is an important component of plant immunity against potentially pathogenic bacteria, acting to recognise the conserved flg22 peptide of flagellin. FLS2 shares the common structure of transmembrane receptor kinases with a receptor-like ectodomain composed of leucine-rich repeats (LRR) and an active intracellular kinase domain. Upon ligand binding, FLS2 dimerises with the regulatory LRR-receptor kinase BRI1-associated kinase 1, which in turn triggers downstream signalling cascades. Although lacking crystal structure data, recent advances have been made in our understanding of flg22 recognition based on structural and functional analyses of FLS2. These studies have revealed critical regions/residues of FLS2 and post-translational modifications that regulate the abundance and activity of this receptor. In this review, we present the current knowledge on the structural mechanism of the FLS2–flg22 interaction and subsequent receptor-mediated signalling.     

Effects of dietary fibre and protein on urea transport across the cecal mucosa of piglets

In ruminants, gastrointestinal recycling of urea is acutely enhanced by fibre-rich diets that lead to high ruminal concentration of short chain fatty acids (SCFA), while high ammonia has inhibitory effects. This study attempted to clarify if urea flux to the porcine cecum is similarly regulated. Thirty-two weaned piglets were fed diets containing protein (P) of poor prececal digestibility and fibre (F) at high (H) or low levels (L) in a 2 × 2 factorial design. After slaughter, cecal content was analyzed and the cecal mucosa incubated in Ussing chambers to measure the effect of pH, SCFA and NH₄ ⁺ on the flux rates of urea, short-circuit current (I _sc) and tissue conductance (G _t). NH₄ ⁺ significantly enhanced I _sc (from 0.5 ± 0.2 to 1.2 ± 0.1 μEq cm^?2 h^?1). No acute effects of SCFA or ammonia on urea flux were observed. Tissue conductance was significantly lower in the high dietary fibre groups irrespective of the protein content. Only the HP-LF group emerged as different from all others in terms of urea flux (74 ± 6 versus 53 ± 3 nmol cm^?2 h^?1), associated with higher cecal ammonia concentration and reduced fecal consistency. The data suggest that as in the rumen, uptake of ammonia by the cecum may involve electrogenic transport of the ionic form (NH₄ ⁺). In contrast to findings in the rumen, neither a high fibre diet nor acute addition of SCFA enhanced urea transport across the pig cecum. Instead, a HP-LF diet had stimulatory effects. A potential role for urea recycling in stabilizing luminal pH is discussed.     

The Kinetics of Mechanically Coupled Myosins Exhibit Group Size-Dependent Regimes

Naturally occurring groups of muscle myosin behave differently from individual myosins or small groups commonly assayed in vitro. Here, we investigate the emergence of myosin group behavior with increasing myosin group size. Assuming the number of myosin binding sites (N) is proportional to actin length (L) (N = L/35.5 nm), we resolve in vitro motility of actin propelled by skeletal muscle myosin for L = 0.2–3 μm. Three distinct regimes were found: L < 0.3 μm, sliding arrest; 0.3 μm ≤ L ≤ 1 μm, alternation between arrest and continuous sliding; L > 1 μm, continuous sliding. We theoretically investigated the myosin group kinetics with mechanical coupling via actin. We find rapid actin sliding steps driven by power-stroke cascades supported by postpower-stroke myosins, and phases without actin sliding caused by prepower-stroke myosin buildup. The three regimes are explained: N = 8, rare cascades; N = 15, cascade bursts; N = 35, continuous cascading. Two saddle-node bifurcations occur for increasing N (mono → bi → mono-stability), with steady states corresponding to arrest and continuous cascading. The experimentally measured dependence of actin sliding statistics on L and myosin concentration is correctly predicted.