Expression of the Xenopus DECD-Box RNA Helicase, XDDX39, during Embryonic Development and Limb Regeneration

A.L. Mescher^1*, M.W. Harty¹, M.C. Muzinich¹, R.C. Smith^2*, A.W. Neff^1* and M.W. King^3*

      Using subtractive hybridizations and gene array techniques (King et al. 2003) we have isolated a variety of genes that are differentially regulated in regeneration competent versus regeneration incompetent Xenopus laevis. One gene we recently cloned from Xenopus hindlimb blastema-enriched cDNA is the homolog of the human DECD-box RNA helicase, DDX39. Expression of such RNA binding proteins has recently been demonstrated in stem cells of several different tissues and identified with the property of "stemness". As an initial approach to determining XDDX39’s significance in embryonic development and possible role in tissue repair and organ regeneration, we have investigated its expression pattern during embryogenesis and limb regeneration using whole mount in situ hybridization. At the neurula stage (stage 17), XDDX39 is localized only to regions around the developing nervous system including the neural tube, neural crest, and to a lesser extent the paraxial mesoderm. At stage 28 expresses appears throughout the CNS and in paraxial mesoderm of the tail bud. Later (stage 30-39) XDDX39 is expressed in the developing abdominal muscle cells as these migrate ventrally. Differentiated myotomes did not express XDDX39. In developing hindlimbs, XDDX39 expression is exclusively mesenchymal and shows labeling in distinct regions at stage 53, localization in digit tips at stage 55, and no expression by stage 57. Expression is more complicated and dynamic, during hindlimb regeneration. In stage 53 and 55 limbs, which retain diminishing capacity for regeneration, faint expression of XDDX39 is seen in blastemas 3 days after amputation, which becomes more prominent at 5 and 7 days. In regeneration-incompetent stage 57 limbs, XDDX39 is up-regulated within 1 day at the level of amputation and continues in 3, 5, and 7 day pseudoblastemas. Expression of XDDX39 in early development and limb regeneration is restricted to undifferentiated cells and or cells at the onset of differentiation, consistent with its postulated involvement in controlling differentiation.

^* Indiana University Center for Regenerative Biology and Medicine
¹ IU School of Medicine Bloomington
² Eli Lilly and Co.
³ IU School of Medicine Terre Haute