Stepwise Progression of Embryonic Patterning

It is long established that the graded distribution of Dorsal transcription factor influences spatial domains of gene expression along the dorsoventral (DV) axis of Drosophila melanogaster embryos. However, the more recent realization that Dorsal levels also change with time raises the question of whether these dynamics are instructive. An overview of DV axis patterning is provided, focusing on new insights identified through quantitative analysis of temporal changes in Dorsal target gene expression from one nuclear cycle to the next (‘steps’). Possible roles for the stepwise progression of this patterning program are discussed including (i) tight temporal regulation of signaling pathway activation, (ii) control of gene expression cohorts, and (iii) ensuring the irreversibility of the patterning and cell fate specification process.

TrendsLevels of Dorsal transcription factor change over time, raising the question of how this morphogen controls patterning of the Drosophila embryo when it is so dynamic.Spatiotemporal examination of a small number of Dorsal target genes had shown that gene expression is also dynamic, and this study was recently expanded using NanoString technology to provide a temporal analysis of ∼70 genes in the Drosophila early embryo.Quantitative, fine-scale temporal data for transcript levels in the early Drosophila embryo have helped to clearly define temporal roles for transcription factors and identify gene expression cohorts, providing new insight into the stepwise progression of the DV patterning gene regulatory network.