Stability and nuclear dynamics of the bicoid morphogen gradient.
Patterning in multicellular organisms results from spatial gradients in morphogen concentration, but the dynamics of these gradients remain largely unexplored. We characterize, through in vivo optical imaging, the development and stability of the Bicoid morphogen gradient in Drosophila embryos that express a Bicoid-eGFP fusion protein. The gradient is established rapidly (approximately 1 hr after fertilization), with nuclear Bicoid concentration rising and falling during mitosis. Interphase levels result from a rapid equilibrium between Bicoid uptake and removal. Initial interphase concentration in nuclei in successive cycles is constant (+/-10%), demonstrating a form of gradient stability, but it subsequently decays by approximately 30%. Both direct photobleaching measurements and indirect estimates of Bicoid-eGFP diffusion constants (D < or = 1 microm(2)/s) provide a consistent picture of Bicoid transport on short ( approximately min) time scales but challenge traditional models of long-range gradient formation. A new model is presented emphasizing the possible role of nuclear dynamics in shaping and scaling the gradient.
Gregor
Thomas
T
Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey 08544, USA. tg2@princeton.edu
Wieschaus
Eric F
EF
McGregor
Alistair P
AP
Bialek
William
W
Tank
David W
DW
D000818:Animals; D019521:Body Patterning; D002467:Cell Nucleus / Q000378:metabolism*; D004058:Diffusion; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000033:anatomy & histology / Q000196:embryology* / Q000235:genetics; D036681:Fluorescence Recovery After Photobleaching; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006706:Homeostasis; D008938:Mitosis / Q000502:physiology; D008954:Models, Biological; D009024:Morphogenesis; D009865:Oocytes / Q000166:cytology / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*
D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; C056478:bcd protein, Drosophila