Genetic analysis of bristle loss in hybrids between Drosophila melanogaster and D. simulans provides evidence for divergence of cis-regulatory sequences in the achaete-scute gene complex.
The two closely related species of Drosophila, D. melanogaster and D. simulans, display an identical bristle pattern on the notum, but hybrids between the two are lacking a variable number of bristles. We show that the loss is temperature-dependent and provide evidence for two periods of temperature sensitivity. A first period of heat sensitivity occurs during larval development and corresponds to the time when the prepattern of expression of genes whose products activate achaete-scute in the proneural clusters preceding bristle precursor formation is established. A second period of cold sensitivity corresponds to the time of emergence of the bristle precursor cells and the maintenance of their neural fate, a process requiring high levels of Achaete-Scute. Expression of achaete-scute at these two critical periods depends on cis-regulatory elements of the achaete-scute complex (AS-C). The differences between males, which have only one copy of the X-linked AS-C from D. simulans, and females, which have copies from both parental species, are compared, together with the effects of crossing in different rearrangements of the D. melanogaster AS-C that delete regulatory and/or coding sequences. We provide evidence that bristle loss in the hybrids may result from a decrease in the level of transcription at the AS-C and argue that interaction between trans-acting factors and cis-regulatory elements within the AS-C has diverged between the two species.
Skaer
N
N
Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, 67404 Illkirch Cedex, C.U. de Strasbourg, France.
Simpson
P
P
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D019521:Body Patterning / Q000235:genetics; D002678:Chimera / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D004330:Drosophila / Q000235:genetics*; D029721:Drosophila Proteins; D004742:Enhancer Elements, Genetic; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D017344:Genes, Insect; D007150:Immunohistochemistry; D008297:Male; D012045:Regulatory Sequences, Nucleic Acid; D013696:Temperature; D014157:Transcription Factors / Q000235:genetics*
D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D014157:Transcription Factors; C089199:ac protein, Drosophila; C089197:sc protein, Drosophila