SPATIAL AND TEMPORAL EXPRESSION OF BASIC FIBROBLAST GROWTH-FACTOR (FGF-2) MESSENGER-RNA AND PROTEIN IN EARLY XENOPUS DEVELOPMENT

We have analyzed the expression pattern of bFGF (FGF-2) mRNA and prote in in early Xenopus development using RNAse protections, in situ hybri dization and immunocytochemical methods. We find that the maternal bFG F mRNA content is at its highest in the previtellogenic oocytes (stage I-II) but decreases during further oogenesis. This low maternal level persists into the early embryonic stages and is uniformly distributed on an RNA basis. Zygotic transcription is turned on both from anterio r and posterior regions but not from the middle region in the mid-neur ula stage, and the expression greatly increases during the late neurul a and tailbud stages. In the tadpole stage, the expression is detected in the brain, eyes, ears and neural crest-derived mesenchyme of the h ead. Also, it is expressed along the mesodermal axis, the level fallin g as the myotomes differentiate. Immunocytochemical study shows abunda nt bFGF protein in early oocytes and much less in later oocytes. The l ocalization is mainly to the nuclei of the early oocytes and to the cy toplasm of the later oocytes. Localization of maternal bFGF protein in the animal hemisphere is observed in the early embryonic stages and s ome reuptake into nuclei occurs by the early blastula stage. The zygot ically synthesized protein starts to be expressed in the anterior regi on of the mid-neurula stage and soon also becomes detectable in the po sterior region. By tailbud and pre-larval stages, this zygotic protein appears to be present along the entire neural and mesodermal axis. Wh en these cases are sectioned it can be seen that bFGF protein is detec ted in most parts of the head. In the posterior domain, it is present in the mesoderm and clearly becomes localized in the muscle cells to t he nuclei and to the cell termini adjoining the intermyotomal septa.