TUESDAY-POSTER PRESENTATIONS limited false discovery (5.8%). Among these 223 genes, 117 have known orthologs of which 68 were up-regulated and 49 were down-regulated. Altered orthologous genes that were discovered via microarray analysis were validated by RT-PCR. Currently, gene expression patterns in the Ciona hearts are being identified via in situ hybridization, including FGF 9/16/20, Foxo, and a non-orthologous heart-specific gene. In combination, these studies will help to elucidate the regulatory mechanisms of cardiac myocyte proliferation by the identification of orthologous genes involved in the development and regeneration of the Ciona myocardium. 2366 Ultrastructure and Immunohistochemical Analyses of a Regenerative Myocardium. L. Washburn 1 , S. Stokes-Cox 1 , P. M. Pardhanani 1 , R. Price 2 , H. Evans-Anderson 1 ; 1 Biology, Winthrop, Rock Hill, SC, 2 Instrumentation Resource Facility, University of South Carolina School of Medicine, Columbia, SC Ciona intestinalis is an invertebrate animal model system that is well characterized and has many advantages for the study of cardiovascular biology. A striking difference between most vertebrates and Ciona is that the Ciona myocardium is capable of regenerating cardiac myocytes throughout its lifespan, which makes the mechanisms of cardiac myocyte proliferation in Ciona intriguing. In order to stimulate regeneration, hearts were injured via ligation around the middle of the heart. After a 24 or 48 hour recovery period, damaged and control hearts were fixed for immunohistochemical or ultrastructure analyses. Preliminary TEM studies show degradation of the myofibrils and changes in the organization of mitochondria in cardiac myocytes. Interestingly, in addition to damaged myocytes, dividing myocytes are also evident and undifferentiated cells populate the damaged myocardium. Furthermore, thickening of the extracellular matrix is apparent, particularly within the lumen of the heart. Histological studies using Mayer’s Hematoxylin and Eosin as well as Movat pentachrome stains show basic organization of the matrix components within the Ciona heart. Specific labeling of the myocardium using the MF20 antibody (Iowa Hybridoma Bank) shows organization of the cardiac myocytes. Studies using immunohistochemistry to identify proliferation and apoptosis in cardiac myocytes of damaged hearts are currently underway. Taken together, these studies will coordinate differences in cellular organization to ultrastructural changes in cardiac myocytes within the regenerative myocardium of Ciona, which will help to elucidate the basic mechanisms of cardiac myocyte proliferation. 2367 FXR, a Novel Receptor in Bone Cell Differentiation and Function. F. M. Moussa 1 , S. L. Lababidi 1 , A. S. Sanyurah 2 , L. N. El-Shaar 1 , K. M. Novak 1 , S. Abdelmagid 1 , Y. Zhang 1 , F. F. Safadi 1 ; 1 Northeast Ohio Medical University, Rootstown, OH, 2 Kent State University, Kent, OH Farnesoid X receptor (FXR), also known as NR1H4 (nuclear receptor subfamily 1, group H, member 4) is a bile acid receptor key in maintaining bile acids and cholesterol homeostasis. FXR is highly expressed in liver and small intestine, where bile acids are synthesized and secreted, respectively. As such, FXR plays an important role in fat metabolism. It has also been found that FXR is an upstream regulator of Fibroblast Growth Factor 21 (FGF-21), which has recently been shown to contribute to bone loss through the inhibition of osteoblastogenesis and stimulation of adipogenesis. While it has long been known that FXR is expressed in liver, intestine, kidney, and adipose tissue, it’s expression and function in bone are not well understood. In this study, we examined the expression of FXR in bone and demonstrate its key regulatory role in osteoblast and osteoclast differentiation and function. We performed qPCR on