ANALYSIS OF THE DEVELOPING XENOPUS TAIL BUD REVEALS SEPARATE PHASES OF GENE-EXPRESSION DURING DETERMINATION AND OUTGROWTH

We have studied Xenopus tail development from the end of gastrulation to the commencement of outgrowth at the tail bud stage. We show that a n early group of genes are expressed at the stage of tail bud determin ation, at the end of gastrulation, and a late group are expressed at a round stage 27 just before tail bud outgrowth. Together, these genes d efine seven distinct regions of the tail bud as outgrowth commences. W e have previously shown that formation of a tail bud depends on the in teraction of three tissue regions, called N, M and C, at stage 13. Her e we show that expression of the late group of genes is dependent on t his NMC interaction. We describe molecular correlates of two of these regions, M and C, which were formerly unobservable and whose existence was inferred from embryological experiments. (C) 1998 Elsevier Scienc e Ireland Ltd.