title: Evolution of the ventral midline in insect embryos.
abstract: The ventral midline is a source of signals that pattern the nerve cord of insect embryos. In dipterans such as the fruitfly Drosophila melanogaster (D. mel.) and the mosquito Anopheles gambiae (A. gam.), the midline is narrow and spans just 1-2 cells. However, in the honeybee, Apis mellifera (A. mel.), the ventral midline is broad and encompasses 5-6 cells. slit and other midline-patterning genes display a corresponding expansion in expression. Evidence is presented that this difference is due to divergent cis regulation of the single-minded (sim) gene, which encodes a bHLH-PAS transcription factor essential for midline differentiation. sim is regulated by a combination of Notch signaling and a Twist (Twi) activator gradient in D. mel., but it is activated solely by Twi in A. mel. We suggest that the Twi-only mode of regulation--and the broad ventral midline--represents the ancestral form of CNS patterning in Holometabolous insects.
authors.affiliation: Department of Molecular and Cell Biology, Division of Genetics, Genomics, and Development, Center for Integrative Genomics, University of California, Berkeley, California 94720, USA.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Zinzen
authors.forename: Jessica
authors.initials: J
authors.lastname: Cande
authors.forename: Matthew
authors.initials: M
authors.lastname: Ronshaugen
authors.forename: Dmitri
authors.initials: D
authors.lastname: Papatsenko
authors.forename: Mike
authors.initials: M
authors.lastname: Levine
mesh_terms: D000818:Animals; D000852:Anopheles / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D001516:Bees / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D005075:Biological Evolution; D019521:Body Patterning; D002490:Central Nervous System / Q000166:cytology* / Q000196:embryology / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism; D004331:Drosophila melanogaster / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D004625:Embryo, Nonmammalian; D004742:Enhancer Elements, Genetic; D007814:Larva / Q000166:cytology / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D051880:Receptors, Notch / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D019076:Transgenes / Q000502:physiology; D051879:Twist-Related Protein 1 / Q000235:genetics / Q000378:metabolism
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D029721:Drosophila Proteins; D009687:Nuclear Proteins; D051880:Receptors, Notch; D051879:Twist-Related Protein 1; C497753:Twi protein, Drosophila; C089449:sim protein, Drosophila