Summary: | Noise is an intrinsic part of biochemical systems such as gene regulation networks. Noisy gene expression has been well documented in populations of single cells, and is likely a key mechanism in evolutionary change. But in developing embryos, cells within a tissue must overcome such variability in order to provide the uniformity required to coordinate multiple events. Reproducibility and determinacy of the spatial protein patterns preceding tissue differentiation is a critical aspect of development. In this study, we use anterior-posterior (AP) segmentation in the fruit fly (\emph{Drosophila}) to understand how gene regulation dynamics control noise. One of the earliest AP patterning events is the anterior activation of the \emph{hunchback} (\emph{hb}) gene by the maternally-derived Bicoid (Bcd) protein gradient. This interaction has been very well characterized, providing the tools for us to develop a stochastic model of \emph{hb} gene regulation to make predictions about expression noise, and to corroborate these experimentally. For \emph{hb}, we show that self-regulation is a critical part of controlling noise, and the multiple Bcd binding sites in the \emph{hb} promoter also enhance pattern reproducibility. To the degree that such features are shared by other genes, these noise-reducing mechanisms may be common to many pattern forming events.
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