Using image-based flow cytometry to monitor satellite cells proliferation and differentiation in vitro

A novel multiplex fluorescent-labeling method for the visualization of mixed-species biofilms in vitro

In nature, bacteria usually exist as mixed-species biofilms, where they engage in a range of synergistic and antagonistic interactions that increase their resistance to environmental challenges. Biofilms are a major cause of persistent infections, and dispersal from initial foci can cause new infections at distal sites thus warranting further investigation. Studies of development and spatial interactions in mixed-species biofilms can be challenging due to difficulties in identifying the different bacterial species in situ. Here, we apply CellTrace dyes to studies of biofilm bacteria and present a novel application for multiplex labeling, allowing identification of different bacteria in mixed-species, in vitro biofilm models. Oral bacteria labeled with CellTrace dyes (far red, yellow, violet, and CFSE [green]) were used to create single- and mixed-species biofilms, which were analyzed with confocal spinning disk microscopy (CSDM). Biofilm supernatants were studied with flow cytometry (FC). Both Gram-positive and Gram-negative bacteria were well labeled and CSDM revealed biofilms with clear morphology and stable staining for up to 4 days. Analysis of CellTrace labeled cells in supernatants using FC showed differences in the biofilm dispersal between bacterial species. Multiplexing with different colored dyes allowed visualization of spatial relationships between bacteria in mixed-species biofilms and relative coverage by the different species was revealed through segmentation of the CSDM images. This novel application, thus, offers a powerful tool for studying structure and composition of mixed-species biofilms in vitro.IMPORTANCEAlthough most chronic infections are caused by mixed-species biofilms, much of our knowledge still comes from planktonic cultures of single bacterial species. Studies of formation and development of mixed-species biofilms are, therefore, required. This work describes a method applicable to labeling of bacteria for in vitro studies of biofilm structure and dispersal. Critically, labeled bacteria can be multiplexed for identification of different species in mixed-species biofilms using confocal spinning disk microscopy, facilitating investigation of biofilm development and spatial interactions under different environmental conditions. The study is an important step in increasing the tools available for such complex and challenging studies.

Finding a Direct Method for a Dynamic Process: The DD (Direct and Dynamic) Cell-Tox Method

The main focus of in vitro toxicity assessment methods is to assess the viability of the cells, which is usually based on metabolism changes. Yet, when exposed to toxic substances, the cell triggers multiple signals in response. With this in mind, we have developed a promising cell-based toxicity method that observes various cell responses when exposed to toxic substances (either death, division, or remain viable). Based on the collective cell response, we observed and predicted the dynamics of the cell population to determine the toxicity of the toxicant. The method was tested with two different conformations: In the first conformation, we exposed a monoculture model of blood macrophages to UV light, hydrogen peroxide, nutrient deprivation, tetrabromobisphenol A, fatty acids, and 5-fluorouracil. In the second, we exposed a coculture liver model consisting of hepatocytes, hepatic stellate cells, Kupffer cells, and liver sinusoidal endothelial cells to rifampicin, ibuprofen, and 5-fluorouracil. The method showed good accuracy compared to established toxicity assessment methods. In addition, this approach provided more representative information on the toxic effects of the compounds, as it considers the different cellular responses induced by toxic agents.

Overexpression of the PLK4 Gene as a Novel Strategy for the Treatment of Autosomal Recessive Microcephaly by Improving Centrosomal Dysfunction

Autosomal recessive microcephaly and chorioretinopathy (MCCRP) is a neurodevelopmental disorder characterized by delayed psychomotor development, growth retardation with dwarfism, and ocular abnormalities, and its occurrence has been found to be closely related to variants of the gene encoding centrosomes. However, the association between centrosomal duplication defects and the etiology of microcephaly syndromes is poorly understood. It is well known that polo-like kinase 4 (PLK4) is a key regulator of centriole duplication, and the abnormalities of centrosomal function caused by its protein variation need to be further explored in the pathogenesis of microcephaly. In our study, we found that a patient with microcephaly and chorioretinopathy harbored compound heterozygous missense variants NM_014264.4: c.2221C > T (p.Gln741*) and NM_014264.4: c.2062 T > C (p.Tyr688His) in the PLK4 gene. Overexpression experiments of the variant PLK4 proteins then showed that the G741 variant rather than the T688H variant had lost centrosomal amplification ability, and the G741 variant but not the T688H variant induced centrosomal replication disorder, which further inhibited cell proliferation, cycle division and cytoskeleton morphology in HeLa cells. Moreover, the overexpression of the two variant proteins had inconsistent effects on the target protein PLK4 by western blot analysis, also indicating that T688H variant overexpression is not functionally equivalent to WT-PLK4 overexpression. Therefore, all data support the idea that the PLK4 mutation induces centriolar duplication disorder and reduces the efficiency of mitosis inducing cell death or cell proliferation in the etiology of microcephaly disorder.

Single-cell assays using integrated continuous-flow microfluidics

The recent maturation of continuous-flow microfluidic technologies has coincided with transformative new methods to profile single cells, including their genetic types, protein expression and enzyme activities. Continuous-flow high-throughput single-cell screening and sorting can reveal relationships across cellular phenotypes (e.g., enzyme activity and secretion) and genetic fingerprints. This technology provides unique opportunities, as well as experimental and computational challenges, for integrative approaches that can process large amounts of single-cell data. In this chapter, we discuss recent advances in integrated continuous-flow microfluidic approaches with a focus on measurements and statistical analysis of single-cell enzyme activity and their applications in quantitative biology, synthetic biology, and diagnosis.