Messages, messengers and the Bicoid protein

SILVINA PONCE DAWSON

Congreso; VI Congreso Argentino de Bioinformática y Biologia Computacional; 2015

The diffusive transport of substances plays a relevant role in manybiological processes. This is particularly relevant in embryogenesiswhere the spatially inhomogeneous distribution of substances called"morphogens" establishes the pattern for the subsequent celldifferentiation. Most often morphogens do not diffuse freely in thecytosol but also interact with various cell components. The nettransport, in such a case, can be described by effective diffusioncoefficients that depend on the morphogen concentration. A casestudied in great detail is that of the establishment of thedorso-ventral axis in embryos of Drosophila melanogaster where thegradient of the transcription factor, Bicoid, is key. The SDD modelhas been proposed to explain the formation of the gradient ofBicoid. In this model Bcd is produced at the anterior end, thendiffuses into the embryo while being degradaded. Measurements of theBcd diffusion coefficient using different optical techniques providedapparently contradictory results which could be explained within aunified model under the assumption that Bcd not only diffuses but alsobinds to sites inside the embryo. In this talk I will discuss whatinformation various optical techniques provide on the net transport ofsubstances that diffuse and react and how the observations on thestationary fluorescence distributions should be interpreted in thiscase. I will also discuss how the interaction affects the formation ofthe gradient of Bicoid and show that a model that includes thisbinding can explain the gradient formation within the experimentallyobserved times.