Figure 9. Rnd3 antagonizes RhoA/ROCK1 signaling during various stages of pregnancy.

(A) In the non-pregnant rabbit uterus, constitutively expressed Rnd3 antagonizes RhoA/ROCK1 signaling which maintains the smooth muscle cells of the uterus in the quiescent state. (B) During the mid-pregnancy stage (15 days) in the rabbit uterus, upregulated Rnd3 antagonizes enhanced RhoA/ROCK1 signaling and maintains the calcium-dependent increase in Ca²⁺ MLCK and tension at a higher level (Ca²⁺ sensitization). This effect can be recovered by treatment of muscle strips from mid-pregnancy myometrium with farnesyl-transferase inhibitor, Manumycin A. (C) During late pregnancy (31 days), upregulation of RhoA and Rho kinase expression is associated with an increase in Ca²⁺ sensitivity of contractile proteins that is inhibited by the Rho kinase inhibitor, Y-27632. MLC: myosin light chain; Ca²⁺-MLCK: Ca²⁺-calmodulin-activated myosin light chain kinase; MCLP: myosin light chain phosphatase.