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IMPORTANCE Time spent in outdoor activities has decreased owing to home confinement for the coronavirus disease 2019 (COVID-19) pandemic. Concerns have been raised about whether home confinement may have worsened the burden of myopia owing to substantially decreased time spent outdoors and increased screen time at home. OBJECTIVE To investigate the refractive changes and prevalence of myopia in school-aged children during the COVID-19 home confinement. DESIGN, SETTING, AND PARTICIPANTSA prospective cross-sectional study using school-based photoscreenings in 123 535 children aged 6 to 13 years from 10 elementary schools in Feicheng, China, was conducted. The study was performed during 6 consecutive years (2015-2020). Data were analyzed in July 2020.EXPOSURES Noncycloplegic photorefraction was examined using a photoscreener device. MAIN OUTCOMES AND MEASURESThe spherical equivalent refraction was recorded for each child and the prevalence of myopia for each age group during each year was calculated. The mean spherical equivalent refraction and prevalence of myopia were compared between 2020 (after home confinement) and the previous 5 years for each age group. RESULTSOf the 123 535 children included in the study, 64 335 (52.1%) were boys. A total of 194 904 test results (389 808 eyes) were included in the analysis. A substantial myopic shift (approximately −0.3 diopters [D]) was found in the 2020 school-based photoscreenings compared with previous years (2015-2019) for younger children aged 6 (−0.32 D), 7 (−0.28 D), and 8 (−0.29 D) years. The prevalence of myopia in the 2020 photoscreenings was higher than the highest prevalence of myopia within 2015-2019 for children aged 6 (21.5% vs 5.7%), 7 (26.2% vs 16.2%), and 8 (37.2% vs 27.7%) years. The differences in spherical equivalent refraction and the prevalence of myopia between 2020 and previous years were minimal in children aged 9 to 13 years.CONCLUSIONS AND RELEVANCE Home confinement during the COVID-19 pandemic appeared to be associated with a significant myopic shift for children aged 6 to 8 years according to 2020 school-based photoscreenings. However, numerous limitations warrant caution in the interpretation of these associations, including use of noncycloplegic refractions and lack of orthokeratology history or ocular biometry data. Younger children's refractive status may be more sensitive to environmental changes than older ages, given the younger children are in a critical period for the development of myopia.

p33cdk2 is a serine-threonine protein kinase that associates with cyclins A, D, and E and has been implicated in the control of the G1/S transition in mammalian cells. Recent evidence indicates that cyclin-dependent kinase 2 (Cdk2), like its homolog Cdc2, requires cyclin binding and phosphorylation (of threonine-160) for activation in vivo. However, the extent to which mechanistic details of the activation process are conserved between Cdc2 and Cdk2 is unknown. We have developed bacterial expression and purification systems for Cdk2 and cyclin A that allow mechanistic studies of the activation process to be performed in the absence of cell extracts. Recombinant Cdk2 is essentially inactive as a histone H1 kinase (< 4 x 10(-5) pmol phosphate transferred.min-1 x microgram-1 Cdk2). However, in the presence of equimolar cyclin A, the specific activity is approximately 16 pmol.mon-1 x microgram-1, 4 x 10(5)-fold higher than Cdk2 alone. Mutation of T160 in Cdk2 to either alanine or glutamic acid had little impact on the specific activity of the Cdk2/cyclin A complex: the activity of Cdk2T160E was indistinguishable from Cdk2, whereas that of Cdk2T160A was reduced by five-fold. To determine if the Cdk2/cyclin A complex could be activated further by phosphorylation of T160, complexes were treated with Cdc2 activating kinase (CAK), purified approximately 12,000-fold from Xenopus eggs. This treatment resulted in an 80-fold increase in specific activity. This specific activity is comparable with that of the Cdc2/cyclin B complex after complete activation by CAK (approximately 1600 pmol.mon-1 x microgram-1). Neither Cdk2T160A/cyclin A nor Cdk2T160E/cyclin A complexes were activated further by treatment with CAK. In striking contrast with cyclin A, cyclin B did not directly activate Cdk2. However, both Cdk2/cyclin A and Cdk2/cyclin B complexes display similar activity after activation by CAK. For the Cdk2/cyclin A complex, both cyclin binding and phosphorylation contribute significantly to activation, although the energetic contribution of cyclin A binding is greater than that of T160 phosphorylation by approximately 5 kcal/mol. The potential significance of direct activation of Cdk2 by cyclins with respect to regulation of cell cycle progression is discussed.

Myostatin is a highly conserved member of the transforming growth factor-β ligand family known to regulate muscle growth via activation of activin receptors. A fusion protein consisting of the extracellular ligand-binding domain of activin type IIB receptor with the Fc portion of human immunoglobulin G (ActRIIB-Fc) was used to inhibit signaling through this pathway. Here, we study the effects of this fusion protein in adult, 18-month-old, and orchidectomized mice. Significant muscle growth and enhanced muscle function were observed in adult mice treated for 3 days with ActRIIB-Fc. The ActRIIB-Fc-treated mice had enhanced fast fatigable muscle function, with only minor enhancement of fatigue-resistant fiber function. The ActRIIB-Fc-treated 18-month-old mice and orchidectomized mice showed significantly improved muscle function. Treatment with ActRIIB-Fc also increased bone mineral density and serum levels of a marker of bone formation. These observations highlight the potential of targeting ActRIIB receptor to treat age-related and hypogonadism-associated musculoskeletal degeneration.

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