Maternal Origins of Developmental Reproducibility

Abstract

Summary Cell fate decisions during multicellular development are precisely coordinated, leading to highly reproducible macroscopic structural outcomes [1–3]. The origins of this reproducibility are found at the molecular level during the earliest stages of development, when patterns of morphogen molecules emerge reproducibly [4, 5]. However, while the initial conditions for these early stages are determined by the female during oogenesis, it is unknown whether reproducibility is perpetuated from oogenesis or reacquired by the zygote. To address this issue in the early Drosophila embryo, we sought to count individual maternally deposited bicoid mRNA molecules and compare variability between embryos with previously observed fluctuations in the Bicoid protein gradient [6, 7]. Here we develop independent methods to quantify total amounts of mRNA in individual embryos and show that mRNA counts are highly reproducible between embryos to within ~9%, matching the reproducibility of the protein gradient. Reproducibility emerges from perfectly linear feed-forward processes: changing the genetic dosage in the female leads to proportional changes in the mRNA and protein numbers in the embryo. Our results indicate that the reproducibility of the morphological structures of embryos originates during oogenesis when initial patterning signals are precisely controlled.

Extending the dynamic range of transcription factor action by translational regulation

“…While such a scheme involving an intermediary maternal mRNA and protein appears wasteful at first glance, here we have shown that it may provide a substantial benefit for information transmission at low input concentration, i.e., in posterior regions of the embryo. Although we are not familiar with any direct measurement of caudal mRNA copy numbers, the copy numbers for the gap genes [79] (and also bicoid [88]) are consistent with the range M ~ 10 2 -10 3 mRNA per nuclear volume.…”

“…There, each mRNA harbors a binding site of size c ~ 1-10 nm, but the mRNAs typically are separated by distances d ~ 1-10 μm. Roughly, we can expect that input readouts will be independent and the ITR mechanism effective so long as M ≲ d/ c ~ 10 2 -10 4 , putting M in the range that we examined and where it appears biologically plausible; recent experiments in the Drosophila and zebrafish embryos and in mammalian cells reported mRNA counts in the range 50-1200 per typical cell volume [79,[87][88][89][90][91]. For such values of M, we find significant increases in capacity of 0.8-1.8 bits at C ~ 0.1-1, with optimal regulatory curves using high…”

Quantitative Single-Embryo Profile ofDrosophilaGenome Activation and the Dorsal–Ventral Patterning Network

“…Two studies have quantified the number of transcripts for two genes included in this study, using FISH to estimate the number of transcripts (Boettiger and Levine 2013;Petkova et al 2014). One study of bcd transcripts prior to the syncytial blastoderm stage and NC10 found 890,000 transcripts.…”

“…The direct detection of messenger RNA (mRNA) molecules minimizes steps between sample collection and data acquisition, reducing error, sample loss, or contamination. RNA-seq has been used in past studies of the Drosophila MZT to quantify the number of transcripts for a gene in the early embryo, and while these studies provide an abundance of data for all genes transcribed, the methods used have been shown to introduce bias in transcript count and read coverage that can hamper absolute quantification of transcripts (Hansen et al 2010;Lott et al 2011;Roberts et al 2011;AliMurthy et al 2013;Petkova et al 2014).…”

Fly wing vein patterns have spatial reproducibility of a single cell

“…a single cell. Indeed, a similar situation has been observed in the early embryo where the precision of molecular patterns that are set up during oogenesis lead to precise molecular patterns in the early embryo all the way to the first macroscopic pattern, the cephalic furrow [12,14,36,37]. This connection between the early embryo and the final adult wing structure indicates that spatial reproducibility of morphogenetic features in the fly may be maintained throughout the entire 10 days of development.…”