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Fifty years have now passed since Parry and Squire proposed a detailed structural model that explained how tropomyosin, mediated by troponin, played a steric-blocking role in the regulation of vertebrate skeletal muscle. In this Special Issue dedicated to the memory of John Squire it is an opportune time to look back on this research and to appreciate John’s key contributions. A review is also presented of a selection of the developments and insights into muscle regulation that have occurred in the years since this proposal was formulated.

Contusion injuries are common in sport, but our knowledge of the responses to injury primarily come from animal studies and research using eccentric exercise. Therefore, the aim of this study was to develop a model of contusion injury in human participants and, additionally, investigate and compare physiological responses to four impact loads. Thirty-two males were exposed to a single impact of either 4.2, 5.2, 6.2 or 7.2kg, dropped from 67 cm, on to the vastus lateralis of one leg. Maximum voluntary and electrically induced quadriceps force, and pressure pain threshold were measured, and blood sampling carried out, prior to and 30min, 24, 48 and 72h post-impact. Magnetic resonance imaging was carried out 24h post-impact to quantify oedema. Despite impact force with 7.2kg (1681.4 ± 235.6 N) not being different to 6.2kg (1690.7 ± 117.6 N), 7.2kg resulted in greater volume of oedema, voluntary force loss, pain and elevations in creatine kinase than the other loads. Although electrically induced force changed over time, post-hoc analysis failed to identify any changes. Interleukin-6 and prostaglandin-E2 did not change over time for any of the loads. Significant correlations were found between oedema volume, pressure pain threshold and maximum voluntary contraction force. This is the first experimental study to investigate traumatic loading of skeletal muscle and the subsequent physiological responses associated with contusion injuries in humans. The absence of immediate elevations in creatine kinase and changes in electrically induced force suggest impact, with forces similar to those experienced in contact sport, does not cause significant, direct damage to skeletal muscle. However, the relationship between oedema volume, changes in pressure pain threshold and maximum voluntary contraction force suggests central inhibition plays a role in contusion-related muscle dysfunction.

Keratins and keratin-associated proteins (KRTAPs) are the main components of mammalian nails and hair. Comparative genomics and gene expression studies have revealed that keratins are conserved in all vertebrates, whereas KRTAPs exist only in mammals. Recently, we found hair keratin-like cysteine-rich keratins in jawless vertebrates with confirmed expression in the cornified epithelial teeth of the sea lamprey (Petromyzon marinus). Here, we report that KRTAP-like proteins are also present in the horny teeth of the lamprey. Mass spectrometry-based proteomics identified proteins that share features with KRTAPs, such as high contents of cysteine and tyrosine residues, which support intermolecular interactions, and abundant glycine residues, which endow the proteins with flexibility. Genes encoding KRTAP-like proteins are arranged in a cluster in P. marinus, and the presence of at least one KRTAP-like protein is conserved in phylogenetically diverse species of lamprey, including Lampetra fluviatilis, Lethenteron reissneri, Geotria australis, and Mordacia mordax. The KRTAP-like genes of lampreys contain two exons, whereas mammalian KRTAPs have only a single exon. Although KRTAPs and KRTAP-like proteins are products of independent evolution, their common expression in cornified skin appendages suggests that they fulfill similar functions.

Over the past three decades community-based natural resources management (CBNRM) has sought to address the concurrent needs of economic development and ecological protection at the local level, but there is often strong divergence between development and conservation interests and successes. In particular, CBNRM has not always led to expected socioeconomic outcomes, while information of its impact on human well-being at household level is sparse. In Botswana, most communities do not disburse benefits from CBNRM ventures to households. This leads to an inherent scale mismatch that arises because the costs of living with wildlife are felt at the household level, while the benefits are paid out at the community or village level. We use longitudinal data from two household surveys conducted 22 years apart to assess if benefits from the Botswana model of CBNRM have increased household-level adaptive capacity for those living with wildlife. We take a livelihoods capital approach to develop indicators of adaptive capacity and measure how livelihood diversity, inequality, and adaptive capacity have changed in five communities in northern Botswana between 1995 and 2017. Our analyses confirm the findings of qualitative reviews and suggest that CBNRM is under-performing in its contribution to improved household-level adaptive capacity. CBNRM cannot be said to benefit communities if the majority of community members do not experience increased well-being. We therefore recommend restructuring the governance models of CBNRM and other community conservation approaches to ensure that benefits are more directly targeted to actively participating households.

DNA methylation and Polycomb are key factors in the establishment of vertebrate cellular identity and fate. Here we report de novo missense mutations in DNMT3A , which encodes the DNA methyltransferase DNMT3A. These mutations cause microcephalic dwarfism, a hypocellular disorder of extreme global growth failure. Substitutions in the PWWP domain abrogate binding to the histone modifications H3K36me2 and H3K36me3, and alter DNA methylation in patient cells. Polycomb-associated DNA methylation valleys, hypomethylated domains encompassing developmental genes, become methylated with concomitant depletion of H3K27me3 and H3K4me3 bivalent marks. Such de novo DNA methylation occurs during differentiation of Dnmt3a W326R pluripotent cells in vitro, and is also evident in Dnmt3a W326R/+ dwarf mice. We therefore propose that the interaction of the DNMT3A PWWP domain with H3K36me2 and H3K36me3 normally limits DNA methylation of Polycomb-marked regions. Our findings implicate the interplay between DNA methylation and Polycomb at key developmental regulators as a determinant of organism size in mammals. Gain-of-function mutations altering the PWWP domain of DNMT3A are identified as a new cause of microcephalic dwarfism. These mutations abrogate DNMT3A binding to H3K36me2 and H3K36me3 and lead to aberrant DNA methylation of Polycomb-marked regions.

The epidermal appendages of birds and reptiles (the sauropsids) include claws, scales, and feathers. Each has specialized physical properties that facilitate movement, thermal insulation, defence mechanisms, and/or the catching of prey. The mechanical attributes of each of these appendages originate from its fibril-matrix texture, where the two filamentous structures present, i.e., the corneous ß-proteins (CBP or ß-keratins) that form 3.4 nm diameter filaments and the α-fibrous molecules that form the 7–10 nm diameter keratin intermediate filaments (KIF), provide much of the required tensile properties. The matrix, which is composed of the terminal domains of the KIF molecules and the proteins of the epidermal differentiation complex (EDC) (and which include the terminal domains of the CBP), provides the appendages, with their ability to resist compression and torsion. Only by knowing the detailed structures of the individual components and the manner in which they interact with one another will a full understanding be gained of the physical properties of the tissues as a whole. Towards that end, newly-derived aspects of the detailed conformations of the two filamentous structures will be discussed and then placed in the context of former knowledge.

With the ongoing COVID-19 (Coronavirus Disease 2019) pandemic, caused by the novel coronavirus SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2), there is a need for sensitive, specific, and affordable diagnostic tests to identify infected individuals, not all of whom are symptomatic. The most sensitive test involves the detection of viral RNA using RT-qPCR (quantitative reverse transcription PCR), with many commercial kits now available for this purpose. However, these are expensive, and supply of such kits in sufficient numbers cannot always be guaranteed. We therefore developed a multiplex assay using well-established SARS-CoV-2 targets alongside a human cellular control ( RPP30 ) and a viral spike-in control (Phocine Herpes Virus 1 [PhHV-1]), which monitor sample quality and nucleic acid extraction efficiency, respectively. Here, we establish that this test performs as well as widely used commercial assays, but at substantially reduced cost. Furthermore, we demonstrate >1,000-fold variability in material routinely collected by combined nose and throat swabbing and establish a statistically significant correlation between the detected level of human and SARS-CoV-2 nucleic acids. The inclusion of the human control probe in our assay therefore provides a quantitative measure of sample quality that could help reduce false-negative rates. We demonstrate the feasibility of establishing a robust RT-qPCR assay at approximately 10% of the cost of equivalent commercial assays, which could benefit low-resource environments and make high-volume testing affordable.

Richard Thompson, Melissa Sambrotta and colleagues show that biallelic mutations in TJP2 cause severe cholestatic liver disease. Their findings suggest that loss of TJP2 protein disrupts the structural integrity of tight junctions in liver tissue, resulting in progressive liver damage. Elucidating genetic causes of cholestasis has proved to be important in understanding the physiology and pathophysiology of the liver. Here we show that protein-truncating mutations in the tight junction protein 2 gene ( TJP2 ) cause failure of protein localization and disruption of tight-junction structure, leading to severe cholestatic liver disease. These findings contrast with those in the embryonic-lethal knockout mouse, highlighting differences in redundancy in junctional complexes between organs and species.

AimsTo describe the prevalence of polypoidal choroidal vasculopathy (PCV) in a Caucasian population with neovascular age-related macular degeneration (NAMD).MethodsAll patients referred to a city AMD service over a 2-year period underwent imaging including Indocyanine Green Angiography at baseline. A panel of experts confirmed the patients with NAMD and diagnosed the lesion type including PCV. The proportion of Caucasian patients with PCV was identified. Two authors independently reviewed clinical imaging and recorded data of patients with PCV on lesion characteristics. Further information including treatments received and visual acuity at different time points was analysed.ResultsA total of 492 patients were diagnosed with NAMD during the 2-year study period. Of these patients, 204 had occult lesions (41.5%). PCV was identified in 45 patients (22.1% of occult NAMD and 9.1% of all NAMD). 23 patients received anti-vascular endothelial growth factor (VEGF) monotherapy, 8 received verteporfin photodynamic therapy (PDT) monotherapy and the remaining 14 patients were managed with combined PDT and anti-VEGF treatment.ConclusionsThe prevalence of PCV in Caucasians is higher than previously reported. Indocyanine Green Angiography should be a standard investigation for all new patients with NAMD, particularly those with occult NAMD, to avoid missing this important subset.