COVID-19 leads small and medium-sized enterprises (SMEs) to survive very hard. The development difficulties of SMEs lead to weak employment and GDP growth in various countries. In the process of COVID-19’s continuous spread, what is the major reason for the difficulties of SMEs? This paper hopes to answer this question by studying SMEs in Beijing. On this basis, this paper uses structural equation model (SEM) to study the relatively fast recovery of SMEs in Beijing, China, to explore the factors affecting SMEs in the pandemic. After detailed desk research and interviews with relevant entrepreneurs, this paper collects 234 valid questionnaires from SMEs in various industries in Beijing with the help of Federation of Industry and Commerce and Chamber of Commerce in Beijing. Then the data is analyzed with the SEM, which shows the relationship between cash flow from financing activities, markets, employees, costs, government policies and the impact of the pandemic. Finally, an impact model of the pandemic on SMEs is established. The result of the model indicates that the direct effect of the pandemic on the market is the most prominent, and government policies can significantly reduce the negative impact of the pandemic on SMEs indirectly. Based on this, this paper puts forward some policy suggestions, such as the targeted issuance of consumption vouchers and the reduction of administrative barriers. This will enable megacities in various countries to improve policy support for SMEs and promote the recovery and development of SMEs.
In vertebrates, the aromatase coded by the cyp19a1a gene can catalyze the conversion from androgens to estrogens. Thus, the regulatory mechanisms of cyp19a1a gene expression are a critical research field in reproductive endocrinology. In this study, we use zebrafish as a model to study the dynamic methylation levels of the cyp19a1a gene core promoter during zebrafish ovarian folliculogenesis. The results show that there is an apparent fluctuation of the methylation levels of zebrafish cyp19a1a core promoter. Moreover, the methylation levels are inversely correlated with the expression levels of cyp19a1a transcripts when the ovarian follicles develop from PV into the MV stage. Also, the CpG dinucleotides which are close to the transcriptional starting site may have provided a significant blocking effect on inhibiting the transcriptional function of RNA polymerase II. Taken together, the results from the present study strongly suggest that DNA methylation was one of mechanisms that are involved in the regulation of cyp19a1a gene expression during folliculogenesis. This methylation mechanism modifying transcriptional process accompanied with zebrafish ovarian folliculogenesis might also shed new light on the regulation of cyp19a1a expression during the ovarian developmental stage in other vertebrates.
Paralytic Shellfish Poisoning (PSP) caused by the dinoflagellate Alexandrium catenella is a wellknown global syndrome that negatively impacts human health and fishery economies. Understanding the population dynamics and ecology of this species is thus important for identifying determinants of blooms and associated PSP toxicity. Given reports of extensive genetic heterogeneity in the toxicity and physiology of Alexandrium species, knowledge of genetic population structure in harmful algal species such as A. catenella can also facilitate the understanding of toxic bloom development and ecological adaptation. In this study we employed microsatellite markers to analyze multiple A. catenella strains isolated from several sub-regions in the Gulf of Maine (GoM) during summer blooms, to gain insights into the sources and dynamics of this economically important phytoplankton species. At least three genetically distinct clusters of A. catenella were identified in the GoM. Each cluster contained representatives from different subregions, highlighting the extent of connectivity and dispersal throughout the region. This shared diversity could result from cyst beds created by previous coastal blooms, thereby preserving the overall diversity of the regional A. catenella population. Rapid spatiotemporal genetic differentiation of A. catenella populations was observed in local blooms, likely driven by natural selection through environmental conditions such as silicate and nitrate/nitrite concentrations, emphasizing the role of short-term water mass intrusions and biotic processes in determining the diversity and dynamics of marine phytoplankton populations. Given the widespread intraspecific diversity of A. catenella in GoM and potentially elsewhere, harmful algal blooms will likely *
Population genetic studies provide insights into intraspecific diversity and dispersal patterns of microorganisms such as protists, which help understanding invasions, harmful algal bloom development and occurrence of seafood poisoning. Spatial genetic differentiation has been reported in many microbial species indicating significant dispersal barriers among different habitats. Temporal differentiation has been less studied and its frequency, drivers, and magnitude are thus relatively poorly understood. The toxic dinoflagellate species Gambierdiscus caribaeus was sampled during 2 years in the Florida Keys, and repeatedly from 2006 to 2016 at St. Thomas, US Virgin Islands (USVI), including a 3-year period with monthly sampling, enabling a comparison of spatial and temporal genetic differentiation. Samples from the USVI site showed high temporal variability in local population structure, which correlated with changes in salinity and benthic habitat cover. In some cases, temporal variability exceeded spatial differentiation, despite apparent lack of connectivity and dispersal across the Greater Caribbean Region based on the spatial genetic data. Thus, local processes such as selection might have a stronger influence on population structure in microorganisms than geographic distance. The observed high temporal genetic diversity challenges the prediction of harmful algal blooms and toxin concentrations, but illustrates also the evolutionary potential of microalgae to respond to environmental change.
Recent evidence suggests that programmed cell death (PCD) can play a role in stress‐induced decline and termination of harmful algal blooms. However, components of the PCD cascade, i.e. reactive oxygen species (ROS) and caspase‐like activity, have also been observed in the absence of exogenous stress, where their activities and functions remain unclear. Here, we characterized the variability of prevalence of cell death, ROS, and caspase‐like activity at different growth phases and diel cycles in cultures of dinoflagellate Karenia brevis. Results show that ROS percentages increased with culture age and fluctuated in a phasing diel pattern, while caspase‐like activity was observed throughout growth. In actively growing K. brevis cells, PCD components may be involved in key metabolic processes, while in stationary phase they may relate to stress acclimation. The circadian diel pattern of ROS may be explained by the balance between the metabolic generation of ROS and circadian rhythmicity of antioxidant enzymes. Overall, this work highlights not only the involvement of PCD components in the growth of marine phytoplankton, but the importance of understanding mechanisms controlling their accumulation, which would help to better interpret their presence in the field.
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