Shaping the scaling characteristics of gap gene expression patterns in Drosophila.
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ABSTRACT:
SUBMITTER: Xu R
PROVIDER: S-EPMC9984453 | biostudies-literature | 2023 Feb
REPOSITORIES: biostudies-literature
Publications
Shaping the scaling characteristics of gap gene expression patterns in <i>Drosophila</i>.
Xu Ruoqing R Dai Fei F Wu Honggang H Jiao Renjie R He Feng F Ma Jun J
Heliyon 20230210 2
How patterns are formed to scale with tissue size remains an unresolved problem. Here we investigate embryonic patterns of gap gene expression along the anterior-posterior (AP) axis in <i>Drosophila</i>. We use embryos that greatly differ in length and, importantly, possess distinct length-scaling characteristics of the Bicoid (Bcd) gradient. We systematically analyze the dynamic movements of gap gene expression boundaries in relation to both embryo length and Bcd input as a function of time. We ...[more]
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Project description:Segmentation of the Drosophila embryo begins with the establishment of spatially restricted gap gene-expression patterns in response to broad gradients of maternal transcription factors, such as Bicoid. Numerous studies have documented the fidelity of these expression patterns, even when embryos are subjected to genetic or environmental stress, but the underlying mechanisms for this transcriptional precision are uncertain. Here we present evidence that every gap gene contains multiple enhancers with overlapping activities to produce authentic patterns of gene expression. For example, a recently identified hunchback (hb) enhancer (located 5-kb upstream of the classic enhancer) ensures repression at the anterior pole. The combination of intronic and 5' knirps (kni) enhancers produces a faithful expression pattern, even though the intronic enhancer alone directs an abnormally broad expression pattern. We present different models for "enhancer synergy," whereby two enhancers with overlapping activities produce authentic patterns of gene expression.
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Project description:BackgroundExtensive variation in early gap gene expression in the Drosophila blastoderm is reduced over time because of gap gene cross regulation. This phenomenon is a manifestation of canalization, the ability of an organism to produce a consistent phenotype despite variations in genotype or environment. The canalization of gap gene expression can be understood as arising from the actions of attractors in the gap gene dynamical system.ResultsIn order to better understand the processes of developmental robustness and canalization in the early Drosophila embryo, we investigated the dynamical effects of varying spatial profiles of Bicoid protein concentration on the formation of the expression border of the gap gene hunchback. At several positions on the anterior-posterior axis of the embryo, we analyzed attractors and their basins of attraction in a dynamical model describing expression of four gap genes with the Bicoid concentration profile accounted as a given input in the model equations. This model was tested against a family of Bicoid gradients obtained from individual embryos. These gradients were normalized by two independent methods, which are based on distinct biological hypotheses and provide different magnitudes for Bicoid spatial variability. We showed how the border formation is dictated by the biological initial conditions (the concentration gradient of maternal Hunchback protein) being attracted to specific attracting sets in a local vicinity of the border. Different types of these attracting sets (point attractors or one dimensional attracting manifolds) define several possible mechanisms of border formation. The hunchback border formation is associated with intersection of the spatial gradient of the maternal Hunchback protein and a boundary between the attraction basins of two different point attractors. We demonstrated how the positional variability for hunchback is related to the corresponding variability of the basin boundaries. The observed reduction in variability of the hunchback gene expression can be accounted for by specific geometrical properties of the basin boundaries.ConclusionWe clarified the mechanisms of gap gene expression canalization in early Drosophila embryos. These mechanisms were specified in the case of hunchback in well defined terms of the dynamical system theory.
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