Function of the Small Guanosine Triphosphate-Binding Protein RhoA in the Process of Implantation*

The Rho family of small GTPases occupies a key position in the control of cell motility and morphology in response to extracellular stimuli. Rho proteins trigger the formation of contractile stress fibers, resulting in regulation of cell motility. We explored the expression and function of RhoA in human endometrium and decidua. RhoA immunoreactivity had a predominantly glandular epithelial distribution in the proliferative phase and midsecretory phase. In decidua, the expression of RhoA was more pronounced in the stromal cells as well as in the glandular epithelium. RhoA protein levels in proliferative phase and midsecretory phase endometrium as well as decidua were evaluated by immunoblotting; a single band of RhoA protein with a molecular mass of 21 kDa was detected in all cell lysates. Cultured human decidual cells were found to have few actin stress fibers. Decidual cells lost their actin stress fibers by the treatment with C3, an exoenzyme produced by Clostridium botulinum, whereas new actin stress fibers appeared in human decidual cells stimulated with lysophosphatidic acid (LPA). Mouse blastocysts became attached to cultured human decidual cells after embryos hatched from the zona pellucida. The majority of hatched blastocysts attached to human decidual cells within 24 h. Blastocysts attached to decidual cells exhibited extensive outgrowth after 48 h in culture. Treatment of decidual cells with C3 exoenzyme or LPA did not affect the rates of hatching and attachment of blastocysts, but outgrowth of embryos on decidual cells was inhibited by C3 exoenzyme treatment in a dosedependent manner. Contrariwise, addition of LPA to decidual cells dose dependently increased the outgrowth of embryos on decidual cells. These findings suggest that RhoA in decidual cells is important for embryonic development and differentiation after attachment. (J Clin Endocrinol Metab 85: 4742‐ 4749, 2000)