The intrinsically disordered protein SPE-18 promotes localized assembly of MSP in Caenorhabditis elegans spermatocytes

ABSTRACTMany specialized cells use unconventional strategies of cytoskeletal control. Nematode spermatocytes discard their actin and tubulin following meiosis, and instead employ the regulated assembly/disassembly of the Major Sperm Protein (MSP) to drive sperm motility. However, prior to the meiotic divisions, MSP is sequestered through its assembly into paracrystalline structures called fibrous bodies (FBs). The accessory proteins that direct this sequestration process have remained mysterious. This study reveals SPE-18 as an intrinsically disordered protein that is essential for MSP assembly within FBs. In spe-18 mutant spermatocytes, MSP forms disorganized cortical fibers, and the cells arrest in meiosis without forming haploid sperm. In wild-type spermatocytes, SPE-18 localizes to pre-FB complexes and functions with the kinase SPE-6 to localize MSP assembly. Changing patterns of SPE-18 localization uncover previously unappreciated complexities in FB maturation. Later, within newly individualized spermatids, SPE-18 is rapidly lost, yet SPE-18 loss alone is insufficient for MSP disassembly. Our findings reveal an alternative strategy for sequestering cytoskeletal elements, not as monomers but in localized, bundled polymers. Additionally, these studies provide an important example of disordered proteins promoting ordered cellular structures.

Spontaneous traveling waves naturally emerge from horizontal fiber time delays and travel through locally asynchronous-irregular states

Sensory neuroscience has focused a great deal of its attention on characterizing the mean firing rate that is evoked by a stimulus, and while it has long been recognized that the firing rates of individual neurons fluctuate around the mean, these fluctuations are often treated as a form of internally generated noise1. There is, however, evidence that these “ongoing” fluctuations of activity in sensory cortex during normal, waking function shape neuronal excitability and responses to external input2,3. We have recently found that spontaneous fluctuations are organized into waves traveling at speeds consistent with the speed of action potentials traversing unmyelinated horizontal cortical fibers (0.1-0.6 m/s)4 across the cortical surface5. These waves systematically modulate excitability across the retinotopic map, strongly affecting perceptual sensitivity as measured in a visual detection task. The underlying mechanism for these waves, however, is unknown. Further, it is unclear whether waves are consistent with the low rate, highly irregular, and weakly correlated “asynchronous-irregular” dynamics observed in computational models6 and cortical recordings in vivo7. Here, we study a large-scale computational model of a cortical sheet, with connections ranging up to biological scales. Using an efficient custom simulation framework, we study networks with topographically-organized connectivity and distance-dependent axonal conduction delays from several thousand up to one million neurons. We find that spontaneous traveling waves are a general property of these networks and are consistent with the asynchronous-irregular regime. These waves are well matched to spontaneous waves recorded in the neocortex of awake monkeys. Further, individual neurons sparsely participate in waves, yielding a sparse-wave regime that offers a unique operating mode, where traveling waves coexist with locally asynchronous-irregular dynamics, without inducing deleterious neuronal correlations8.

The Mechanical Harvesting of Hemp Using In-Field Stand-Retting: A Simpler Approach Converted to the Production of Fibers for Industrial Use

The mechanical harvesting of hemp is a key step toward a profitable use of the product. Various fractions (fiber, seeds, residual biomass) may be recovered, and their correct management is fundamental for complying with the requirements of processors/end users. In the light of the renewed interest for its industrial use (panels and insulators), this work proposes the use of modified commercial machines to implement a field separation of the fibrous fraction of stand-retted hemp, a practice that would be profitable if realized with the systems adopted for textile use. The present work was conducted to test the efficiency of harvesting partially macerated plants by using a modified self-propelled forage harvester (SPFH). In Northern Italy, a hemp crop was stand-retted for four months. Then, an SPFH—with rotor knives reduced in number from 24 to 12—was used. Stand-retting made it possible to separate cortical fibers from the inner stem cylinder during harvesting; 53.3% of the material (fibers and shives) was separated automatically by the SPFH together with the chopped bast fiber, while the remaining 46.7% was separated on exiting the launch tube. More than 50% of the fibers were shorter than 5 cm in length, while almost 15% were longer than 10 cm. The SPFH had an effective operating speed of 3.48 km h−1, and no clogging occurred during the test. Therefore, the combination of stand-retting with harvesting using a modified SPFH could be helpful in obtaining an early separation of fibers from shives, thus facilitating the product treatment during its subsequent processing, e.g., by enhancing the defibration.

Microstructural damage of the cortico-striatal and thalamo-cortical fibers in Fabry disease: a diffusion MRI tractometry study

Purpose Recent evidences have suggested the possible presence of an involvement of the extrapyramidal system in Fabry disease (FD), a rare X-linked lysosomal storage disorder. We aimed to investigate the microstructural integrity of the main tracts of the cortico-striatal-thalamo-cortical loop in FD patients. Methods Forty-seven FD patients (mean age = 42.3 ± 16.3 years, M/F = 28/21) and 49 healthy controls (mean age = 42.3 ± 13.1 years, M/F = 19/28) were enrolled in this study. Fractional anisotropy (FA), axial (AD), radial (RD), and mean diffusivity (MD) maps were computed for each subject, and connectomes were built using a standard atlas. Diffusion metrics and connectomes were then combined to carry on a diffusion MRI tractometry analysis. The main afferent and efferent pathways of the cortico-striatal-thalamo-cortical loop (namely, bundles connecting the precentral gyrus (PreCG) with the striatum and the thalamus) were evaluated. Results We found the presence of a microstructural involvement of cortico-striatal-thalamo-cortical loop in FD patients, predominantly affecting the left side. In particular, we found significant lower mean FA values of the left cortico-striatal fibers (p = 0.001), coupled to higher MD (p = 0.001) and RD (p < 0.001) values, as well as higher MD (p = 0.01) and RD (p = 0.01) values at the level of the thalamo-cortical fibers. Conclusion We confirmed the presence of an alteration of the extrapyramidal system in FD patients, in line with recent evidences suggesting the presence of brain changes as a possible reflection of the subtle motor symptoms present in this condition. Our results suggest that, along with functional changes, microstructural damage of this pathway is also present in FD patients.

Uniaxial loading induces a scalable switch in cortical actomyosin flow polarization and reveals mechanosensitive regulation of cytokinesis

During animal development, it is crucial that cells can sense and adapt to mechanical forces from their environment. Ultimately, these forces are transduced through the actomyosin cortex. How the cortex can simultaneously respond to and create forces during cytokinesis is not well understood. Here we show that under mechanical stress, cortical actomyosin flow switches its polarization during cytokinesis in the C. elegans embryo. In unstressed embryos, longitudinal cortical flows contribute to contractile ring formation, while rotational cortical flow is additionally induced in uniaxially loaded embryos. Rotational cortical flow is required for the redistribution of the actomyosin cortex in loaded embryos. Rupture of longitudinally aligned cortical fibers during cortex rotation releases tension, initiates orthogonal longitudinal flow and thereby contributes to furrowing in loaded embryos. A targeted screen for factors required for rotational flow revealed that actomyosin regulators involved in RhoA regulation, cortical polarity and chirality are all required for rotational flow and become essential for cytokinesis under mechanical stress. In sum, our findings extend the current framework of mechanical stress response during cell division and show scaling of orthogonal cortical flows to the amount of mechanical stress.

Lacomucinaea, a new monotypic genus in Thesiaceae (Santalales)

A new monotypic genus from southern Africa is described based on Thesium lineatum. Lacomucinaea lineata has a number of vegetative and floral morphological features that differ from Thesium and other members of Thesiaceae. An apparently unique feature of the plant is the presence of succulent, fusiform, terete leaves that are caducous, eventually leaving a persistent petiolar stub. The stem surface shows striations formed by cortical fibers inside raised ridges. Anatomically, this type of primary phloem fiber bundle also occurs in Osyridicarpos. A molecular phylogenetic analysis using nuclear ribosomal ITS and the chloroplast trnLF spacer for representatives of all genera in Thesiaceae showed that Lacomucinaea is sister to Osyridicarpos, further supporting this relationship suggested by stem anatomy characters. Recognizing this taxon as a distinct genus results in the genus Thesium being monophyletic. A key to all genera in Thesiaceae is provided.