CELL POLARITY AND MORPHOGENETIC PROPERTIES OF FISCHER RAT THYROID CELLS FRT CULTURED IN SUSPENSION OR EMBEDDED IN DIFFERENT GELS

We have investigated the ability of cloned rat thyroid epithelial cells (FRT) to form polarized structures. When FRT cells were cultured in suspension on agarose-coated dishes compact cell aggregates readily formed. By 8 hours the cells of the outer layer of the aggregate were polarized and exposed microvilli and tight junctions toward the culture medium. If aggregates were further cultured in suspension they reorganized into cysts resembling the inverted follices previously described. Cyst formation also occurred in a completely defined medium. The functional polarity of the cells was assessed by the polarized budding of VSV and Sindbis virus. If aggregates were embedded in a collagen, gelatin or agarose gel, instead of suspension, the polarity of the cells of the outer layer inverted (basal side toward the culture medium) and lumina formed within the aggregates. We propose a model describing the steps involved in this simple morphogenetic process occurring in vitro.