Maternal patterning in early Drosophila embryos: how much information can single maternal gradients supply?

Anterior-posterior patterning in Drosophila relies on positional information supplied by the graded distributions of three maternally supplied transcription factors originally identified in large-scale mutagenesis screens. Here, I examine the development of embryos in which these three maternal gradients have been flattened, but set at different levels. Following such manipulations, expression patterns at the blastoderm stage are uniform along the anterior-posterior axis, but their specific nature depends on the combination and concentration level of the three systems. Each of the three gradients are then examined in contexts in which the others are flattened but set at different levels. This reveals that each system generates a greater fraction of the wild-type pattern than that deleted when that system is removed by loss-of-function mutations, with the exact pattern depending on the levels to which the two remaining flattened systems are set. These simplified patterns are then used to analyze interactions between the maternal systems and to investigate how the pattern of gap and pair rule genes are modulated by network interactions downstream of the maternal inputs themselves.