When it pays to rush: interpreting morphogen gradients prior to steady-state

Area of Science:

• Developmental Biology
• Systems Biology
• Biophysics

Background:

• Morphogen gradients establish precise gene expression boundaries during embryonic development.
• Fluctuations are inherent in biological systems, posing challenges to positional accuracy.
• Emerging evidence suggests morphogen gradients may be interpreted before reaching a steady state.

Purpose of the Study:

• To investigate the positional precision of gene expression boundaries determined by pre-steady-state morphogen gradients.
• To analyze the impact of embryo-to-embryo fluctuations, internal noise, and measurement timing variations.
• To compare the robustness of transcription factor morphogens versus cell-surface receptor morphogens.

Main Methods:

• Analysis of two experimentally motivated models of morphogen gradient formation.
• Mathematical modeling to simulate gradient dynamics and positional precision.
• Inclusion of parameters representing biological noise and measurement timing variability.

Main Results:

• Transcription factor morphogens are sensitive to internal noise when interpreted pre-steady-state, hindering early measurement.
• Cell-surface receptor morphogens maintain positional precision when measured pre-steady-state if measurement timing is consistent.
• Pre-steady-state interpretation is advantageous against embryo-to-embryo fluctuations for receptor-mediated morphogens.

Conclusions:

• Bicoid (Drosophila transcription factor) is unlikely to be interpreted before reaching steady-state due to noise sensitivity.
• Activin (Xenopus) and Nodal (zebrafish) (receptor-mediated morphogens) can be decoded in pre-steady-state.
• The mechanism of morphogen interpretation significantly impacts robustness to developmental noise.