Debra Goldman-Wohl, PhD¹, Caryn Greenfield, MSc¹, Iris Eisenberg, PhD¹, Galia Skarzinsky, PhD², Tal Imbar, MD¹, Ronit Haimov-Kochman, MD¹, Polina Denichenko, PhD³, Rotem Karni, PhD³, Ilana Ariel, MD, PhD² , Sandra Blois, MD⁴ and Simcha Yagel, MD¹.

¹Magda and Richard Hoffman Center for Placenta Research, Obstetrics and Gynecology, ²Pathology, ³Biochemistry and Molecular Biology, IMRIC, Hebrew University-Hadassah Medical School, Jerusalem, Israel. ⁴Universitätsmedizin Charité, Berlin, Germany

Introduction: The progenitor cytotrophoblast of the human placenta can differentiate by fusion to the syncytiotrophoblast or to the invasive extravillous trophoblast. Rbfox2, an RNA-binding protein, controls tissue-specific alternative splicing in diverse processes such as epithelial to mesenchyme transition and myoblast cell fusion. The placenta represents a singular system where two diverse activities of Rbfox2 regulation, cell invasion and cell fusion, may be studied.   Our preliminary results suggest that Rbfox2, by conferring mRNA diversity, may act as a master regulator in trophoblast differentiation to either the fusion or invasive pathways.  In this investigation we characterize the contribution of Rbfox2 to trophoblast differentiation in both mouse and human placenta.
Materials and Methods: Rbfox2 immunohistochemistry/immunofluorescence was performed on human and murine placental tissue sections in normal pregnancy and in placental pathologies.  Inhibition of Rbfox2 alternative splicing in isolated primary trophoblasts was evaluated by immunofluorescence and BhCG.

Results: Trophoblast lineage specific expression of Rbfox2 was observed in both normal and pathological human placentas. Rbfox2 is expressed in the progenitor cytotrophoblast, reduced in the terminally differentiated syncytiotrophoblast and conversely, highly expressed in an increasing gradient of expression in the invasive trophoblasts. Reduced Rbfox2 expression was observed in fused primary trophoblast cell culture with inhibition of Rbfox2 upregulating BhCG production. Murine Rbfox2 expression changes as gestation progresses.  As compared to normal pregnancy, decreased staining was observed in a spontaneous abortion prone model, and more intense staining observed in a preeclampsia model.

Conclusions: Rbfox2, an alternative splicing factor, is differentially expressed in specific trophoblast cell lineages and may act as the molecular switch determining the trophoblast differentiation pathway with implications to several human pregnancy disorders including preeclampsia, fetal growth restriction, and preterm labor.