Network of interactions among pair-rule genes regulating paired expression during primordial segmentation of Drosophila.
A model of the trans-regulation of the Drosophila pair-rule segmentation gene, paired (prd), has been derived from the observed alterations in the distribution of prd transcripts during early embryogenesis in single and double pair-rule mutants. Important aspects of the model include the following features and implications: (i) The regulation of prd is subject to a regulatory hierarchy among pair-rule genes. In particular, it shows that prd is at the bottom of this hierarchy, mediating the transition from pair-rule to segment-polarity genes. The transition of the early 'pair-rule' to the 'segment-polarity' pattern of prd expression is regulated by the secondary pair-rule genes opa and odd. The model predicts the distributions of pair-rule gene products regulating prd at late syncytial blastoderm, e.g., that of opa. (ii) The initial activation of prd is independent of pair-rule genes. (iii) The regulation of prd is combinatorial and hence probably cooperative. Combination of one pair-rule gene product with different pair-rule proteins may lead to opposite regulatory effects on prd. Furthermore, we discuss a two-step conversion of the initial analogue specification of position along the anteroposterior axis into a digital code specified by combinations of active segment-polarity and homeotic genes.
Baumgartner
S
S
Institute of Molecular Biology II, University of Zurich, Switzerland.
Noll
M
M
D000818:Animals; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics*; D004625:Embryo, Nonmammalian / Q000648:ultrastructure; D005786:Gene Expression Regulation; D005796:Genes; D005801:Genes, Homeobox; D008957:Models, Genetic; D014158:Transcription, Genetic