Cell Biology

Adult stem cells not only maintain tissue homeostasis but are also critical for tissue regeneration during injury. Skeletal stem cells are multipotent stem cells that can even generate bones and cartilage upon transplantation to an ectopic site. This tissue generation process requires essential stem cell characteristics including self-renewal, engraftment, proliferation, and differentiation in the microenvironment. Our research team has successfully characterized and isolated skeletal stem cells (SSCs) from the cranial suture called suture stem cells (SuSCs), which are responsible for craniofacial bone development, homeostasis, and injury-induced repair. To assess their stemness features, we have demonstrated the use of kidney capsule transplantation for an in vivo clonal expansion study. The results show bone formation at a single-cell level, thus permitting a faithful assessment of stem cell numbers at the ectopic site. The sensitivity in assessing stem cell presence permits using kidney capsule transplantation to determine stem cell frequency by limiting dilution assay. Here, we described detailed protocols for kidney capsule transplantation and limiting dilution assay. These methods are extremely valuable both for the evaluation of skeletogenic ability and the determination of stem cell frequency.

While wound healing in humans occurs primarily through re-epithelization, in rodents it also occurs through contraction of the panniculus carnosus, an underlying muscle layer that humans do not possess. Murine experimental models are by far the most convenient and inexpensive research model to study wound healing, as they offer great variability in genetic alterations and disease models. To overcome the obstacle of contraction biasing wound healing kinetics, our group invented the splinted excisional wound model. While other rodent wound healing models have been used in the past, the splinted excisional wound model has persisted as the most used model in the field of wound healing. Here, we present a detailed protocol of updated and refined techniques necessary to utilize this model, generate results with high validity, and accurately analyze the collected data. This model is simple to conduct and provides an easy, standardizable, and replicable model of human-like wound healing.

Human neuron transplantation offers novel opportunities for modeling human neurologic diseases and potentially replacement therapies. However, the complex structure of the human cerebral cortex, which is organized in six layers with tightly interconnected excitatory and inhibitory neuronal networks, presents significant challenges for in vivo transplantation techniques to obtain a balanced, functional and homeostatically stable neuronal network. Here, we present a protocol to introduce human induced pluripotent stem cell (hiPSC)-derived neural progenitors to rat brains. Using this approach, hiPSC-derived neurons structurally integrate into the rat forebrain, exhibit electrophysiological characteristics, including firing, excitatory and inhibitory synaptic activity, and establish neuronal connectivity with the host circuitry.

For years, the mammary gland serves as a perfect example to study the self-renew and differentiation of adult stem cells, and the regulatory mechanisms of these processes as well. To assess the function of given genes and/or other factors on stemness of mammary cells, several In vitro assays were developed, such as mammospheres formation assay, detection of stem cell markers by mRNA expression or flow cytometry and so on. However, the capacity of reconstruction of whole mount in the cleared fat pad of recipient female mice is a golden standard to estimate the stemness of the cells. Here we described a step-by-step protocol for in vivo mammary gland formation assay, including preparation of “cleared” recipients and mammary cells for implantation, the surgery process and how to assess the experimental results. Combined with manipulation of mammary cells via gene editing and /or drug treatment, this protocol could be very useful in the researches of mammary stem cells and mammary development.

Xenograft models, and in particular the mouse xenograft model, where human cancer cells are transplanted into immunocompromised mice, have been used extensively in cancer studies. Although these models have contributed enormously to our understanding of cancer biology, the zebrafish xenograft model offers several advantages over the mouse model. Zebrafish embryos can be easily cultured in large quantities, are small and easy to handle, making it possible to use a high number of embryos for each experimental condition. Young embryos lack an efficient immune system. Therefore the injected cancer cells are not rejected, and the formation of primary tumors and micrometastases is rapid. Transparency of the embryos enables imaging of primary tumors and metastases in an intact and living embryo. Here we describe a method where GFP expressing tumor cells are injected into pericardial space of zebrafish embryos. At four days post-injection, the embryos are imaged and the formation of primary tumor and distant micrometastases are analyzed.

Uveal melanoma (UM) is a malignant intraocular tumor in adults. Metastasis develops in almost half of the patients and over 90% of the metastases are in the liver. With the advances in molecular targeting therapy for melanoma, a proper metastasis animal model is of increasing importance for testing the accuracy and effectiveness of systemic therapies. Here, we describe a xenograft model for mimicking human UM liver metastasis by injecting human UM cells into the vitreous cavity in nude mice. The athymic nude mice are immunocompromised and suitable for xenograft tumor growth and metastasis, and intravitreal injection of cells is a quicker and easier operation under a binocular scope, thereby it is simple and effective to test human UM growth and metastasis.