Almost all biomedical research to date has relied upon mean measurements from cell populations, however it is well established that what it is observed at this macroscopic level can be the result of many interactions of several different single cells. Thus, the observable macroscopic ‘average’ cannot outright be used as representative of the ‘average cell’. Rather, it is the resulting emerging behaviour of the actions and interactions of many different cells. Single‐cell RNA sequencing (scRNA‐Seq) enables the comparison of the transcriptomes of individual cells. This provides high‐resolution maps of the dynamic cellular programmes allowing us to answer fundamental biological questions on their function and evolution. It also allows to address medical questions such as the role of rare cell populations contributing to disease progression and therapeutic resistance. Furthermore, it provides an understanding of context‐specific dependencies, namely the behaviour and function that a cell has in a specific context, which can be crucial to understand some complex diseases, such as diabetes, cardiovascular disease and cancer. Here, we provide an overview of scRNA‐Seq, including a comparative review of emerging technologies and computational pipelines. We discuss the current and emerging applications and focus on tumour heterogeneity a clear example of how scRNA‐Seq can provide new understanding of a complex disease. Additionally, we review the limitations and highlight the need of powerful computational pipelines and reproducible protocols for the broader acceptance of this technique in basic and clinical research.

Dermal papilla cells (DPCs) are an important element of the hair follicle (HF) niche, widely used as an in vitro model to study hair growth-related research. These cells are usually grown in 2D culture, but this system did not show efficient therapeutic effects on HF regeneration and growth, and key differences were observed between cell activity in vitro and in vivo. Recent studies have showed that DPCs grown in 3D hanging spheroids are more morphologically akin to an intact DP microenvironment. In this current study, global gene molecular analysis showed that the 3D model highly affected cell adhesion molecules and hair growth-related pathways. Furthermore, we compared the expression of signalling molecules and metabolism-associated proteins of DPCs treated with minoxidil (an FDA-approved drug for hair loss treatment) and 3,4,5-tri-O-caffeoylquinic acid (TCQA) (recently found to induce hair growth in vitro and in vivo) in 3D spheroid hanging drops and a 2D monolayer using DNA microarray analysis. Further validations by determining the gene and protein expressions of key signature molecules showed the suitability of this 3D system for enhancing the DPC activity of the hair growth-promoting agents minoxidil and TCQA.

IntroductionDermal papilla cells (DPc) is an important element in studying the hair follicle (HF) niche. The human hair follicle dermal papilla cells (HFDPC) are widely used as an in vitro model to study hair growth related research. These cells are usually grown in 2D culture, nevertheless, this system did not show efficient therapeutic effect on HF regeneration and growth, and key differences were observed between cell activity in vitro and in vivo. ObjectiveRecent studies have showed that HFDPC grown in 3D hanging spheroids is more morphologically akin to intact DPc microenvironment. This current study showed that the 3D model is applicable to the commercial cell line with new insights on its variability by comparing to previous studies of gene signature restored by 3D culture.Methods and Results Our data demonstrated that HFDPCS grown in 3D in vitro model can influence not only hair growth-related pathways but also immune system -related pathways compared to 2D cell monolayer. Furthermore, we compared the expression of signalling molecules and metabolism-associated proteins of HFDPC in minoxidil (FDA approved drug for hair loss treatment) and 3,4,5-tri-O-caffeoylquinic acid (TCQA) (recently found to induce hair growth in vitro and in vivo) treated 3D and 2D cell cultures using microarray analysis. Conclusion Further validation of the results confirms the suitability of this cell line for 3D model while providing new insights such as to the mechanisms behind the hair growth effects of 3D spheroid treated with hair growth promoting agents.