Tissue-specific developmental expression of OAX, a Xenopus repetitive element

Approximately 1% of the Xenopus laevis genome consists of highly repetitive DNA known alternatively as OAX (for Oocyte Activation in Xenopus), Satelli te I, or Repetitive HindIII Monomer 2. Present as tandemly repeated units o f approximately 750 base pairs, OAX encodes a family of small RNA species t ranscribed by RNA polymerase III. Although the subject of many of the class ic studies on early embryonic gene regulation, reports on OAX expression re main contradictory and incomplete. Using whole-mount in situ hybridization and RNase protection assays, we have therefore examined in detail the expre ssion pattern of OAX in Xenopus embryos of various stages. OAX is initially expressed during gastrula stages; by tailbud stages embryos display discre te zones of expression at the dorsal boundary of the cement gland, in the d eveloping somites and differentiating skeletal muscle, as well as in the do rsal aspect of the neural tube. These data demonstrate that OAX is expresse d in a dynamic pattern under tight spatial and temporal regulation. (C) 200 0 Elsevier Science Ireland Ltd. All rights reserved.