Expression of murineHOXD9 during embryonic joint patterning and in human T lymphotropic virus type Itax transgenic mice with arthropathy resembling rheumatoid arthritis

Abstract

Objective. To characterize the expression of mu-rine HOXD9 during normal joint development and in arthritic joints of human T lymphotropic virus type I (HTLV-I) tax transgenic mice and the role of HTLV-I tax in HOXD9 expression. Methods. Expression of HOXD9, HOXD10, HOXD11, HOXD12, and HOXD13 genes in joint tissues at the ankle/foot regions of mouse embryos at day 10 to day 18 of gestation (E10-E18) and neonates within 10 days after birth was determined by reverse transcriptase-polymerase chain reaction and in situ reverse transcription methods. Adult synovial tissues from 5 HTLV-I tax transgenic mice with chronic poly-arthritis and 4 nontransgenic (normal) mice were also examined for expression of these HOXD genes. The effect of HTLV-I on HOXD9 expression in cultured synoviocytes was studied by in vitro infection and trans-fection experiments. Results. Expression of HOXD9 was detected in embryonic joints, preferentially on articular cartilage, only during the early stages of joint development (up to E15), whereas other HOXD genes were expressed throughout the embryonic and neonatal stages. In adult mice, transcripts of HOXD9 were specifically detected in synovial tissues from 4 of 5 arthritic mice, especially in the lining and sublining synovial cells, but not in synovial tissues of normal mice. Activation of HOXD9 was observed in cultured synoviocytes infected with HTLV-I in vitro as well as in those transfected with HTLV-I tax. Conclusion. Our findings suggest that HOXD9 is involved not only in the early stages of normal joint development, but may also be involved in the pathologic process of arthritis. HTLV-I tax appeared as an activa-tor of this HOX gene in cultured synoviocytes. The embryogenesis of synovial joints is of particular interest because analysis based on observations in normal subjects should expand our knowledge of the pathologic processes in various joint diseases. Joint embryogenesis is a complex process and is classically divided into 2 major morphologic events: formation of the cartilaginous anlages and subsequent joint formation. A number of studies have identified specific changes in certain cellular and molecular factors during joint development (1-5). The regulatory mechanisms of these processes, however, remain unclear. Homeobox (HOX) genes are known to encode transcriptional regulators involved in cell type-specific differentiation and control of the patterning of the body plan in vertebrates (6). A number of HOX genes, particularly the Drosophila AbdB-related (5-located) members of the HOXD complex (formerly known as HOX5 and later as HOX4), are thought to be involved in limb formation in mice and chicks (7-11). These genes are expressed in the developing limbs in domains that are spatially and temporally specific, but overlapping, depending on the developmental stage, and are thought to control segment identity and direct limb patterning and specification (12). Moreover, mutational analyses of