13-P091 Co-ordination of cell-cycle and cell fate determination in the Xenopus retina: An interplay of p27Xic1, Cyclin/cdks and NM23 proteins

XEN cells are derived from an early stage murine embryo and represent an in vitro model of extraembryonic endoderm, an extraembryonic tissue that is essential for the proper development of the embryo. Visceral endoderm, a subtype of extraembryonic endoderm, is known to directly influence epiblast development through several inductive (and anti-inductive) events. In contrast, while the parietal endoderm (another subtype of extraembryonic endoderm) is important for early nutritive support of the embryo, it does not possess any known patterning properties. At present, we are limited to using culture conditions in which XEN cells closely resemble parietal endoderm, thus restricting our ability to study visceral endoderm. To improve the utility of the XEN cell culture model we have been investigating ways to generate visceral endoderm and its various subtypes. A simple method for differentiating between visceral and parietal endoderm is that whilst visceral endoderm is E-cadherin-positive, parietal endoderm is E-cadherin-negative. We have used this cell surface adhesion molecule to quantitatively assess the levels of visceral versus parietal endoderm in different culture conditions. We have found that (i) cell density, (ii) TGFbeta superfamily signalling, and (iii) type of extracellular matrix significantly influence the presence of E-cadherin-positive visceral endoderm within XEN cell cultures. The generation of visceral endoderm from XEN cells will be a significant step towards modelling early developmental events ex vivo.