The Quantification of Bicoid in Early Drosophila Development

Abstract

The quantification of Bicoid in early Drosophila development is a necessary step in evaluating the accuracy of transcriptional models that explain anterior-posterior patterning in the embryo. Previous attempts to quantify Bicoid used western blotting or two-photon microscopy strategies and presented values over a hundred fold lower than other tested Drosophila transcription factors. I conducted an analysis of the biochemical and microscopy strategies previously used to determine the accuracy and reproducibility of Bicoid quantification. To do this, I established two new non-antibody based biochemical strategies which I used to determine total Bicoid quantity during nuclear cycle fourteen. I used confocal microscopy on formaldehyde fixed and live preparations of embryos to determine the molar concentrations of nuclear Bicoid. My results indicate that there are approximately 35,000 Bicoid molecules/nucleus at the anterior of the embryo and ~2400 Bicoid molecules/nucleus at fifty percent embryo length. The total quantity of Bicoid in the embryo at maximum expression is ~2.4 ×108 molecules. An analysis of Bicoid distribution in the cortical and yolk compartments of the embryos suggests that the anterior-posterior gradient of Bicoid is generated by an embryo-wide diffusion mechanism punctuated by an active or passive mode of Bicoid uptake at the nuclei.