TITLE Identification of differentially regulated genes during elongation and early implantation in the ovine trophoblast using cDNA array screening. SHORT TITLE Gene expression in ovine trophoblast KEY WORDS sheep, trophoblast, elongation, implantation, cDNA array, gene expression, protein trafficking genes. AUTHORS

Following hatching, pre-elongated conceptuses undergo elongation by intense proliferation, until implantation. We investigated the changes in gene expression associated with these physiological events using human cDNA arrays containing 2370 known genes. Comparison of pre-elongated, elongated and implanting trophoblasts allowed for determination of 313 expressed genes of which 63 were differentially regulated. These were classified into 4 functional families. Preelongated trophoblasts were characterized by preferential expression of genes involved in protein trafficking, whereas only latter developmental stages expressed cell signaling genes and receptors. Among the 63 developmentally regulated genes, 4 exhibited the highest levels of expression (TMSB10, CTNNA1, NMP1 and CX3CL1). Each of them also represents a functional family and display a specific expression pattern. One of them, CX3CL1 (CX3C chemokine also known as fractalkine) is a chemokine which seems of potential importance for trophoblast development and which will deserve further clarification of its exact role in the context of implantation.