The human placenta is a critical organ formed during pregnancy that possesses an array of specialized metabolic, hormonal, and immunological functions that control the growth and viability of the fetus and, in turn, the health of the mother [1–4]. The importance of proper placental development to the health and well being of the fetus and mother is illustrated in conditions that arise during pregnancy such as preeclampsia, gestational diabetes and intrauterine growth restriction, that are thought to be the result of placental abnormalities .
In the human fetal placenta, the floating villi represent the majority of the chorionic villi and are bathed in maternal blood to function in hormone transport and to aid in the exchange of gases, nutrients and waste between the mother and fetus [2, 5]. The floating villi consist of an outer multinucleated syncytiotrophoblast layer, an underlying mitotically active mononuclear cytotrophoblast layer and a stroma . In the cytotrophoblast layer, polarized stem cytotrophoblast cells proliferate and daughter cells then differentiate and fuse with existing syncytiotrophoblast to maintain the multi-nucleated layer [reviewed by ]. Morphometric analyses have indicated that in the first trimester there is an excess of villous cytotrophoblast cells fusing with the syncytiotrophoblast – likely necessary for the metabolic integrity of the syncytiotrophoblast , although Ellery et al  has recently demonstrated that a proportion of nuclei in the syncytiotrophoblast are actively engaged in transcription in accordance with the high metabolic and secretory activity of the tissue. While proliferation of villous cytotrophoblast cells falls with advancing gestation, the cytotrophoblast layer is not entirely discontinuous. Mori et al  and Jones et al  have calculated ~45–80% continuity of the cell layer at term with cytotrophoblast cells being transformed into flat cells with many thin cellular interdigitating processes. While the events leading to maintenance of the cytotrophoblast stem cell population as well as cytotrophoblast differentiation and fusion are poorly understood, it is becoming clear that initiation of an apoptosis cascade occurs early in differentiation [11, 12]. A flip of phosphatidylserine within the cytotrophoblast cell membrane is also associated with cytotrophoblast fusion [7, 13]. Since the villous cytotrophoblast and syncytiotrophoblast comprise the epithelial covering of the chorionic villi that is in contact with maternal blood, any disturbances in the processes of cytotrophoblast proliferation and fusion of cytotrophoblast with overlying syncytiotrophoblast can seriously perturb the turnover and function of the syncytiotrophoblast layer and ultimately may contribute to development of fetal growth restriction or preeclampsia .
Research has demonstrated that syncytin-1, a retroviral envelope protein, appears to have a direct role in human trophoblast fusion . Furthermore, glial cells missing-1 (GCM1), a transcription factor, appears to be upregulated in pre-fusing cytotrophoblast and to regulate syncytin-1 mRNA expression [15–17]. Along with these findings, other proteins or groups of proteins such as protein tyrosine kinases and protein tyrosine phosphatases with a variety of other known functions also appear to play important roles in the fusion pathway [18, 19]. An intracellular serine/threonine kinase named Integrin-linked kinase (ILK) localizes to focal adhesions and is critically involved in the adhesion of cells to their extracelluar environment and in signal transduction [20, 21]. ILK interacts with the cytoplasmic domains of β-integrins and numerous cytoskeletal associated proteins and has been found to mediate protein-protein interactions.
Recently, Elustondo et al  reported that ILK was highly detectable by immunoblot analyses in human chorionic villous tissue lysates throughout gestation. It was also highly expressed in situ in villous cytotrophoblast cells and in stromal mesenchyme in first trimester and early second trimester human chorionic floating villi; however, it was scarcely detected in the syncytiotrophoblast layer. The adherens junction protein E-cadherin mediates homophilic calcium- dependent cell adhesion in neighbouring cells and is also highly detectable at points of cytotrophoblast cell-cell contact [23, 24]. E-cadherin expression markedly decreases with remodeling of cell-cell adhesion complexes associated with differentiation and subsequent fusion of cytotrophoblast to syncytiotrophoblast  and, thus, presence/absence of the protein can be used to assess trophoblast syncytialization [25–27]. As yet, the mechanism(s) underlying the downregulation of E-cadherin expression in villous cytotrophoblast undergoing the morphogenetic process of syncytialization is unknown.
Hannigan et al  has demonstrated that over-expression of ILK in epithelial cells results in disrupted cell-cell adhesion. ILK also downregulates E-cadherin expression through activation of the transcriptional repressor Snail, independent of β-catenin/T cell factor (TCF7) regulation . Based on the reported role of ILK in regulating E-cadherin expression and the known expression of both ILK and E-cadherin expression in the cytotrophoblast of human chorionic villi during pregnancy, we hypothesized that ILK could be a player in regulating the differentiation and fusion of cytotrophoblast into the syncytiotrophoblast via the downregulation of E-cadherin. To begin testing this hypothesis we employed a well documented cell line model, BeWo cytotrophoblast cells, for the study of trophoblast syncytialization [30, 31].