Study on myofibroblast differentiation in the stromal cells of Wharton's jelly: expression and localization of alpha-smooth muscle actin.

To confirm the characteristics of the stromal cells of Wharton's jelly, we investigated the morphological changes in these cells during each trimester of pregnancy. We evaluated the cytoskeletal features of these cells by examining immunohistochemically the localization of one of the contractile proteins, alpha-smooth muscle actin (ASMA). After the second trimester, the stromal cells of Wharton's jelly were stained with ASMA antibody, exhibited the ultrastructural characteristics of the myofibroblasts, and began to express numerous microfilaments in the cytoplasm. Postembedding immunogold labeling detected immunoreactivity for ASMA on these microfilaments. The finding indicated that the stromal cells of Wharton's jelly undergo a time-dependent maturation involving the differentiation of myofibroblasts during the last 6 months of pregnancy. These cells possess a contractile function that may help to protect the umbilical vessels from compression, considering that ASMA was detected in the microfilamentous bundles.