T-tubules are long plasma membrane invaginations that form contact sites with two adjacent endoplasmic reticulum compartments to generate a skeletal muscle triad. Although the importance of t-tubules is well established, and abnormalities are found in multiple muscle disorders, the mechanisms of t-tubule growth are currently unknown. We found that the branched actin nucleator Arp2/3 regulates t-tubule organisation in myofibers. Cortical actin limits t-tubule growth, suggesting that it must be locally disassembled to allow the t-tubule to grow. T-tubule overgrowth is limited by Arpc5-containing Arp2/3 iso-complexes, but not those containing Arpc5L. Loss of Arpc5 results in malformed t-tubule clusters, impaired triads, and asynchronous muscle contraction, as found in multiple muscle disorders. Therefore, limiting t-tubule overgrowth has a role in triad formation and myofiber contraction, providing a possible pathophysiological mechanism for these muscle disorders. ### Competing Interest

During clathrin-mediated endocytosis, a patch of flat plasma membrane is internalized to form a vesicle. In mammalian cells, how the clathrin coat deforms the membrane into a vesicle remains unclear and two main hypotheses have been debated. The ‘constant area’ hypothesis assumes that clathrin molecules initially form a flat lattice on the membrane and deform the membrane by changing its intrinsic curvature while keeping the coating area constant. The alternative ‘constant curvature’ hypothesis assumes that the intrinsic curvature of the clathrin lattice remains constant during the formation of a vesicle while the surface area it covers increases. Previous experimental studies were unable to unambiguously determine which hypothesis is correct. In this paper, we show that these two hypotheses are only two extreme cases of a continuum of vesiculation pathways if we account for the free energies associated with clathrin assembly and curvature generation. By tracing the negative gradient o

First analysis of stable isotopes in rye from northern and eastern Germany provides insights into the early history of rye cultivation from the migration to the late medieval period. A comparison of the δ15N with modern experiments reveals that already the early cultivation involved the practice of intensive manuring. The intensity of manuring does not demonstrate a discernible trend over time but high variability. In some instances, it is likely that rye was cultivated as part of a rotation cultivation system including manuring. Through its δ34S values some rye turned out to be manured with marine peats. Rye, reputed to be a frugal crop, was cultivated on poor sandy soils to a limited extent only. Statistically significant correlation between the 13C content and yields demonstrates that the highest yield success on dwelling mounds was achieved, while the majority of fields on dry sandy soils yielded in relation only 40 to 70 %. Manured rye facilitated the emergence of multi-headed vil

The ovarian reserve defines female reproductive lifespan, which in humans spans decades due to the maintenance of meiotic arrest in non-growing oocytes (NGO) residing in primordial follicles. Unknown is how the chromatin state of NGOs is established to enable long-term maintenance of the ovarian reserve. Here, we show that a chromatin remodeler, CHD4, a member of the Nucleosome Remodeling and Deacetylase (NuRD) complex, establishes chromatin states required for formation and maintenance of the ovarian reserve. Conditional loss of CHD4 in perinatal mouse oocytes results in acute death of NGOs and depletion of the ovarian reserve. CHD4 establishes closed chromatin at regulatory elements of pro-apoptotic genes to prevent cell death and at specific genes required for meiotic prophase I to facilitate the transition from meiotic prophase I oocytes to meiotic arrested NGOs. In addition, CHD4 establishes closed chromatin at the regulatory elements of pro-apoptotic genes in male germ cells, all

Optic nerve (ON) regeneration in mammalian systems is limited by an overshadowing dominance of inhibitory factors. This has severely hampered the identification of pro-regenerative pathways. Here, we take advantage of the regenerative capacity of larval zebrafish to identify pathways that promote ON regeneration. From a small molecule screen, we identified modulators of serotonin (5-HT) signaling that inhibit ON regeneration. We find several serotonin type-1 receptor genes are expressed in RGC neurons during regeneration and that inhibiting 5-HT1 receptors or components of the 5-HT pathway selectively impedes ON regeneration. We show that 5-HT1 receptor signaling is dispensable during ON development yet is critical for regenerating axons to emerge from the injury site. Blocking 5-HT receptors once ON axons have crossed the chiasm does not inhibit regeneration, suggesting a selective role for 5-HT receptor signaling early during ON regeneration. Finally, we show that agonist-mediated ac

The hair bundle of auditory and vestibular hair cells converts mechanical stimuli into electrical signals through mechanoelectrical transduction (MET). The MET apparatus is built around a tip link that connects neighboring stereocilia that are aligned in the direction of mechanosensitivity of the hair bundle. Upon stimulation, the MET channel complex responds to changes in tip-link tension and allows a cation influx into the cell. Ca2+ influx in stereocilia has been used as a signature of MET activity. Using genetically encoded Ca2+ sensors (GCaMP3, GCaMP6s) and high-performance fluorescence confocal microscopy, we detect spontaneous Ca2+ transients in individual stereocilia in developing and fully formed hair bundles. We demonstrate that this activity is abolished by MET channel blockers and thus likely originates from putative MET channels. We observe Ca2+ transients in the stereocilia of mice in tissue explants as well as in vivo in zebrafish hair cells, indicating this activity is

MeCP2 is a DNA-binding transcriptional regulator that is present at near-histone levels in mammalian cortical neurons. Originally identified as a DNA methylation reader, MeCP2 has been proposed to repress transcription by recruiting corepressors to methylated DNA. While some genome-wide occupancy studies support a preference for methylated DNA, others suggest that MeCP2 binding is more influenced by DNA sequence and accessibility than methylation status. Moreover, multiple studies also suggest a role for MeCP2 in gene activation. To clarify MeCP2 function we expressed MeCP2 in Saccharomyces cerevisiae , which lacks DNA methylation and known MeCP2 corepressors. We find that MeCP2 is toxic to yeast and globally inhibits transcription, indicating that MeCP2 can have significant functional impacts without DNA methylation or mammalian corepressors. A subset of MeCP2 mutations that cause the neurodevelopmental disorder Rett syndrome, particularly those that map to the DNA binding domain, all

Rice is the most important source of daily calories in human diets and second only to wheat as the most important protein source. Rice is generally exposed to high ammonium (NH4+) levels in the rhizosphere but may employ both NH4+ and nitrification-derived nitrate (NO3-) as major sources of nitrogen. However, the genetic basis underlying rice adaptation to different nitrogen forms remains poorly characterized. Here, we assessed biomass under either NH4+ or NO3- as a sole nitrogen source in 390 accessions from the USDA Rice Diversity Panel 1. Rice effectively used either form of nitrogen to support early growth. Tolerance to a high-NH4+ exposure was correlated with biomass under NO3- and lower NH4+ levels. Both genotype and nitrogen source strongly influenced biomass accumulation and partitioning between shoot and root. Root showed the greatest biomass variability and sensitivity to nitrogen source. Genome-wide analyses identified 176 single nucleotide polymorphism (SNP) markers associa

Bracts, the leaves subtending flowers, were lost multiple times in angiosperms, including in Brassicaceae, where their development is blocked early. Arabidopsis mutants that restore bract formation suggest that flower identity genes suppress the vegetative program of bract development, but the exact mechanisms and the evolutionary origin of bract loss remain unclear. We exploited natural variation in bracts that form only at the base of flowering branches in Arabidopsis, to study bract development and its connection to floral transition. We combined multiscale phenotyping, quantitative genetics, meristem imaging, time-series transcriptomics and curve registration to capture the genetic and developmental mechanisms unlocking bract development during floral transition. We mapped four Quantitative Trait Loci controlling bracts, excluding known bract mutant genes. We demonstrated LEAFY and other flower regulators were not involved and identified lists of new candidate genes and pathways, s

The Drosophila Ejaculatory duct (ED) is a secretory tissue of the somatic male reproductive system. The ED is involved in the secretion of seminal fluid components and ED-specific antimicrobial peptides that aid in fertility and the female post-mating response. The ED is composed of secretory epithelial cells surrounded by a layer of innervated contractile muscle. The ED grows in young adult males during the first 24h post-eclosion, but the cell cycle status of the ED secretory cells and the role of post-eclosion ED growth have been unexplored. Here, we show that secretory cells of the adult Drosophila ED undergo variant cell cycles lacking mitosis called the endocycle, that lead to an increase in the cell and organ size of the ED post eclosion. The cells largely exit the endocycle by day 3 of adulthood, when the growth of the ED ceases, resulting in a tissue containing cells of ploidies ranging from 8C-32C. The size of the ED directly correlates with the ploidy of the secretory cells,