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Successful implantation requires the synchronization of viable embryonic development with endometrial receptivity. The mechanisms allowing for the initiation of crosstalk between the embryo and the endometrium remain elusive; however, recent studies have revealed that there are alterations in endometrial microRNAs (miRs) in women suffering repeated implantation failure and that one of the altered miRs is miR-145. We assessed the role of miR-145 and its target IGF1R, in early implantation. miR-145 overexpression and IGF1R knockdown were achieved in Ishikawa endometrial cells. Quantitative PCR, western blotting and 3'UTR luciferase reporter assays confirmed that IGF1R is a direct target of miR-145 in the endometrium. Attachment of mouse embryos or IGF1-coated beads to endometrial epithelial cells was used to study the effects of altered miR-145 and/or IGF1R expression on early implantation events. miR-145 overexpression or specific reduction of IGF1R impaired attachment in both cases. An IGF1R target protector prevented the miR-145-mediated reduction in IGF1R and reversed the effect of miR-145 overexpression on attachment. The data demonstrate that miR-145 influences embryo attachment by reducing the level of IGF1R in endometrium.

Trypsinized BHK cells become attached to glass that has been derivatized with a variety of lectins with well-defined specificity for cell-surface carbohydrates. Provided a threshold concentration of glass-immobilized protein is present the cells undergo a transformation to a wellspread morphology. The matrix density of lectins (ricin and concanavalin A) required to trigger this morphological transformation is higher by 10 to 40-fold than the value determined earlier (Hughes, Pena, Clark & Dourmashkin, 1979) for fibronectin. Cells resistant to the toxic lectin, ricin, and expressing 10% or less of ricin-binding carbohydrate groups at their cell surfaces require correspondingly greater matrix densities of ricin to promote active cell spreading. All cell lines spread equally well on concanavalin A-based matrices consistent with their similar binding properties. The quantitative interaction of complementary molecules on the cell surface and matrix, promoting cell adhesion, is demonstrated by these results and a model is proposed for the events leading to a well-spread cell morphology on a protein-coated substratum.

The kinetics of spreading of trypsinized FL cells on plastic or glass substrata covalently or passively coated with various proteins to make simplified model extracellular matrices have been measured. Kinetics have also been obtained in the presence and absence of serum and amniotic fluid. Data from such experiments are shown to be sigmoid and have been computer-fitted with great accuracy to 12 mathematical models discussed in the accompanying paper. A log normal distribution function is shown to give the best fit over 18 different types of experiment. For the first time, therefore, such data can be characterized quantitatively and compared. We obtain the simple parameters μ(mean time to spread) and a (standard error of the mean) and show that the cells spread most rapidly in amniotic fluid or on fibronectin ‘carpets’. They also spread rapidly on a fibronectin-fibrinogen complex extracted from placenta. Spreading is slower in serum, in amniotic fluid lacking fibronectin and on type I collagen or cellular microexudate from FL cells or fibroblasts. On concanavalin A, spreading is rapid but the distribution of times to spread (as expressed by cr) is relatively wide.

The spreading of cells on suitably treated surfaces is briefly discussed and the need to analyse this phenomenon numerically is emphasized. Possible mathematical models for fitting experimental data are classified as statistical, kinetic or empirical and examples of each of these types are given. A possible protocol for analysing cell spreading kinetics and determining goodness of fit and parameter redundancy is presented.