STRIPE FORMING ARCHITECTURE OF THE GAP GENE SYSTEM

In this report, we show that gap genes encode exactly one set of pair- rule stripes, which occur in the native even-skipped position. The cor e of this work is a detailed analysis that shows how this conclusion f ollows from the arrangement of gap domains in the embryo. This analysi s shows that: (1) pattern forming information is transmitted from gap io pair-rule genes by means of a nonredundant sei of morphogenetic gra dients, and (2) the stripe forming capability of the gap genes is cons trained by the arrangement of these gradients and by the fact thai eac h gap domain consists of a pair of correlated gradients. We also show that in the blastoderm, the regulatory sign of a transcriptional regul ator is unlikely io change in a concentration dependent manner. The pr incipal analytic tool used to establish these results is the gene circ uli method. Here, this method is applied io examine hybrid data sets c onsisting of real gene expression data for four gap genes and hypothet ical pair-rule expression data generated by translating native even-sk ipped data along the anterior-posterior axis. In this way, we are able to investigate the stripe forming capabilities of the gap gene system in complete absence of pair-rule cross regulation. We close with an i nference about evolutionary development. ii is argued thai the constra ints on gap gene architecture identified here are a consequence of sel ective pressures that minimize the number of gap genes required io det ermine segments in long-germ band insects. (C) 1998 Wiley-Liss, Inc.