Mouse embryonic stem (ES) cells are continuous cell lines derived directly from the fetal founder tissue of the pre-im- plantation embryo and can be expanded in vitro and give rise to cells from ectodermal, mesodermal and endodermal layers. Mouse ES cells can be maintained and their numbers expanded by culture on feeder layer cells with LIF present in the culture medium. This study shows that changes in seeding density can significantly influence cell number expansion rates. Culturing ES cells in the absence of feeder layer cells and LIF stimulates EB formation when cultured in non-adherent culture plates. Formation of EBs particularly numbers, size of EBs formed, rates of cell proliferation within EBs and viability of cells can also be controlled based on seeding density. All these factors are important for optimizing approaches to co-ordinate differentiation towards a specific cell type. A key goal of ES cell research is to develop specific functional cell types which can be potentially used to study mechanisms of tissue development and as a therapy to repair or replace damaged or diseased tissues.
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