Title: Characterization of Smooth Muscle Cell Development Using Stem Cells and Zebrafish
Other Titles: Karakterisering van gladde-spiercelontwikkeling met behulp van stamcellen en zebravis
Authors: Sohni, Abhishek
Issue Date: 17-Dec-2012
Abstract: Smooth muscle cells (SMCs) are the only muscle cells that have very diverse developmental origin. They can arise from multiple different embryonic tissues during development including neural crest, splanchic mesoderm, local mesenchyme as well as transdifferentiation from endothelial cells. SMCs play a vital role in embryonic development; hence embryos lacking SMCs do not survive. Owing to this developmental significance and diversity in origin, the study and characterization of SMCs has been limited. SMCs are characterized by presence of multiple cytoskeletal and structural proteins such as smooth muscle actin, calponin, multiple isoforms of myosin heavy and light chains as well as smoothelin among others. Expression of SMC characteristic genes is regulated by two major transcription factor (TF) complexes, i.e. MYOCARDIN-SRF and Gata binding protein – 6 (GATA6). Identification and characterization of these SMC gene regulators was performed using either SMC lines or SMC like derivatives form carcinomas. In this work, we employ adult stem cells with near embryonic stem cell properties as a model to derive SMC differentiation, and thus characterize genes (especially TFs) involved in this process. We used bone marrow (BM) derived Multipotent Adult Progenitor Cells of rat origin ((r)MAPC) described in 2002. rMAPCs have characteristics similar to the nascent hypoblast and have the ability to differentiate to endodermal and mesodermal derivatives. More recently (2012) our lab demonstrated that similar cells could be isolated directly from the blastocyst with higher efficiency, called HypoSC. The first objective of this work was to demonstrate if these hypoblast like stem cell derived from BM (rMAPCs) or from blastocyst (HypoSCs) can be efficiently differentiated to SMCs. Clones derived from multiple independent isolations from BM or blastocyst were used to differentiate towards SMCs, using a previously described protocol.We show that rMAPCs and HypoSCs could be efficiently differentiated to SMC like cells that not only express multiple SMC gene mRNAs but also have high levels of the respective protein with characteristic fibrous expression pattern. We further demonstrated that rMAPC derived SMCs, when injected into matrigel plugs in the back of mice, associated with the host vasculature to form a SMC coating around the murine endothelium. This strongly suggests that the differentiation of rMAPCs indeed commits them to a SMC fate.The second aim of this work was to use this methodology to characterize the genome-wide transcriptional changes required for SMC commitment. We performed a time course micro-array experiment to identify TFs with previously unknown SMC function. Using a robust algorithm, previously described, we identified a list of differentially regulated genes that included TFs, among others. We identified and characterized a TF belonging to the SWI/SNF chromatin remodeling complex family – SMARCD3 or BAF60c. These complex proteins participate in multiple developmental and physiological processes including maintenance of embryonic stem cell pluripotency. BAF60c in particular has been shown to be important for development of skeletal and cardiac muscle. We here demonstrate a role of BAF60c in regulation of SMC genes, by binding to the promoter regions of SMC genes and associates with the previously described SMC transcription factors complex, MYOCARDIN-SRF. We thus show that using the rMAPC-SMC differentiation methodology, it is possible to identify TFs (and other genes?) with previously unknown smooth muscle function.We also aimed to characterize vascular SMC development in zebrafish to determine if this model organism could be used for high throughput screening of the function of putative SMC genes. As the presence of vascular SMCs in zebrafish embryos was not well characterized, we first characterized vascular SMC development. Previous in situ hybridization studies in the lab demonstrated that zebrafish embryos and larvae exhibit a SMC gene expression pattern similar to that of vascular endothelial cells. Using a transgenic zebrafish line, we further characterized found that endothelial cells themselves express SMC transcripts, and that there appears to not be an additional SMC layer surrounding the vasculature other than the endothelial cells. Furthermore, we saw presence of high levels of collagen surrounding these endothelial cells, which also expressed smooth muscle actin. In conclusion we demonstrated that rMAPCs can be differentiated to functional SMCs. This system enabled us to identify previously unknown SMC TFs and other genes involved in SMC development. As we focused only on a single TF, there is likely still a wealth of information in the differentially regulated gene list generated in this thesis. We can also conclude that as zebrafish embryos lacks vascular SMCs and this model organism may not be suited for high throughput screening of putative SMC specific genes, In addition, it will be of interest to trace the origin of SMCs seen surrounding blood vessels in adult fish, that seem to be lacking during embryogenesis.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Embryo and Stemcells (-)

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