Tissue engineering: in vitro embryonal nidation in a murine endometrial construct.

The epithelial and mesothelial cellular components of organs can be obtained as dissociated cells using adequate procedures of enzymatic digestion followed by pycnotic separation on density gradients. Using a specially developed procedure for tissue dissociation, the epithelial and connective tissue components of endometria from pseudopregnant mice were grown in culture using a combination of three dimensional culture of connective tissue components in collagen gel, with the superimposition of epithelial components in liquid medium on the surface of the gells. After a few days of growth, when the cultures became dense, murine blastocysts obtained on postcoital day 4.5 by fallopian flushing of hormonally primed and mated mice, were transferred onto the imitated endometria. The blastocysts hatched and grew on the endometrial epithelium as spherical coherent conglomerates of cells quite different from hatched blastocysts grown on the surface of a petri dish, in which the presumtive trophoblasts spred around the central mass. Light and electronmicroscopy of resin embeded sections (2 days after nidation on the simulated endometria) revealed that at least two populations of cell types were recognisable as layers. This is interpreted as an early sign of morphogenesis and the first visible steps of differentiation. The presence of mitotic figures indicates viability and continuing growth. Electronmicroscopy of cell types grown under conditions simulating in vivo tissue architectonics showed overtly less cytopathology and better cell function. Simulated endometria may, therefore, serve as an attractive model for studying early mammalian embryogenesis and the effects of toxic agents.