The growth and development of murine blastocysts provides a relatively simple model for understanding embryonic cell proliferation, differentiation, and morphogenesis. As such, biological axioms driving cell sorting and patterning during early embryogenesis represent a recurring focus of research in developmental biology. The understanding of the basic principles in embryonic structure formation holds profound implications and potential to provide insights into the mechanisms of organogenesis and for application in tissue engineering and regenerative medicine. Our experimental findings suggest that the force of differential adhesive affinity can be overcome by even subtle polarity generated from strong bilateral ligation of highly adhesive cells in determining cell sorting patterns.

The surface polarity was observed as an actin cap contiguously spanning across the apical surface of multiple adjacent cells, though independent of the formation of tight junctions. In contrast to the naive aggregates, the mature aggregates presented polarized, highly adhesive cells at the outer layer. The outer wild-type cells of the more mature aggregates did not differentiate into endoderm, which is known to be able to sort to the exterior from previous studies. However, in further study of more mature cell aggregates, the initial sorting pattern reversed, with the highly adhesive wild-type ES cells forming an outer shell enveloping the less adhesive E-cadherin-deficient cells, contradicting Steinberg’s sorting principle. ResultsĪs observed previously, in aggregates of wild-type and E-cadherin-deficient ES cells, the cell assemblies exhibited an initial sorting pattern showing wild-type cells engulfed by less adhesive E-cadherin-deficient ES cells, which fits the pattern predicted by the differential adhesive hypothesis proposed by Malcom Steinberg. Here, we further explored the principles and mechanisms underlying the phenomenon of spontaneous tissue organization by studying aggregation and sorting of mouse embryonic stem (ES) cells with differential adhesive affinity in culture. The classic experiment undertaken by Townes and Holtfreter demonstrated the ability of dissociated embryonic cells to sort and self-organize spontaneously into the original tissue patterns. Mammalian early development comprises the proliferation, differentiation, and self-assembly of the embryonic cells.

The Culture Chamber by Jeffrey D. Stalk