High mobility of bicoid captured by fluorescence correlation spectroscopy: implication for the rapid establishment of its gradient.
The Bicoid (Bcd) morphogen is essential for pattern formation in fruit flies. It forms an exponential concentration gradient along the embryo AP axis and turns on cascades of target genes in distinct anterior domains. The most commonly accepted model for gradient formation assumes that Bcd travels by simple diffusion and is uniformly degraded across syncytial embryos, yet several recent studies have challenged these ideas. Here, the question of Bcd mobility was investigated using fluorescence correlation spectroscopy in live Drosophila melanogaster embryos. Bcd-EGFP molecules were found to be highly mobile in the cytoplasm during cycles 12-14, with a diffusion coefficient approximately 7 microm(2)/s. This value is large enough to explain the stable establishment of the Bcd gradient simply by diffusion before cycle 8, i.e., before the onset of zygotic transcription.
Abu-Arish
Asmahan
A
Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada.
Porcher
Aude
A
Czerwonka
Anna
A
Dostatni
Nathalie
N
Fradin
Cécile
C
D000818:Animals; D004058:Diffusion; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000196:embryology / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000378:metabolism; D036681:Fluorescence Recovery After Photobleaching; D049452:Green Fluorescent Proteins / Q000378:metabolism; D018398:Homeodomain Proteins / Q000378:metabolism*; D008954:Models, Biological; D019913:Nuclear Localization Signals / Q000378:metabolism; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013050:Spectrometry, Fluorescence / Q000379:methods*; D015534:Trans-Activators / Q000378:metabolism*
D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D019913:Nuclear Localization Signals; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; C056478:bcd protein, Drosophila; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins