Abstract
Tissue expansion and patterning are integral to development, but it is unknown quantitatively how a mother accumulates molecular resources to invest in the future of instructing robust embryonic patterning. Here we develop a model, Tissue Expansion-Modulated Maternal Morphogen Scaling (TEM3S), to study scaled anterior-posterior patterning in Drosophila embryos. Using both ovaries and embryos, we measure a core quantity of the model, the scaling power of the Bicoid (Bcd) morphogen gradient’s amplitude nA. We also evaluate directly model-derived predictions about Bcd gradient and patterning properties. Our results show that scaling of the Bcd gradient in the embryo originates from, and is constrained fundamentally by, a dynamic relationship between maternal tissue expansion and bcd gene copy number expansion in the ovary. This delicate connection between the two transitioning stages of a life cycle, stemming from a finite value of nA ~ 3, underscores a key feature of developmental systems depicted by TEM3S.
Highlights
Tissue expansion and patterning are integral to development; it is unknown quantitatively how a mother accumulates molecular resources to invest in the future of instructing robust embryonic patterning
We found that a general property of the embryo relevant to Bcd gradient scaling is that the amount of maternally deposited bcd mRNA is correlated with embryo size[23,29]
In addition to connecting the events that take place in two distinct stages of Drosophila life cycle, the TEM3S model provides a unified view of the two distinct scenarios of Bcd gradient scaling from an evolutionary perspective at a mechanistic level
Summary
Tissue expansion and patterning are integral to development; it is unknown quantitatively how a mother accumulates molecular resources to invest in the future of instructing robust embryonic patterning. To provide a unified perspective suitable for evaluating diverse systems at different levels, we can define the relationship between tissue specification (patterning) and tissue expansion (growth) of a given developmental system based on how they are connected temporally within a time period of interest These two events can take place either concurrently or with one preceding the other, representing three basic types of temporal relationships or temporal logics (Fig. 1a). In addition to connecting the events that take place in two distinct stages of Drosophila life cycle, the TEM3S model provides a unified view of the two distinct scenarios of Bcd gradient scaling (that is, within-species versus across-species) from an evolutionary perspective at a mechanistic level
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