Cells interpret both the quantity and direction of morphogen signals to decide fate, with signaling guiding development toward liver, kidney, brain, or other tissues.

Intro: Cells establish their position and identity in the body through morphogen gradients and gene expression, guiding tissue development and regeneration.

But the system isn’t perfect: gradient stability has limits, and the full set of signals and backup cues—beyond morphogens—remain incompletely mapped.

Safeguards exist when misexpression occurs, including imbalances in morphogen ratios and potentially electric or mechanical cues that help mitigate errors.

Gradients are actively maintained by production and degradation dynamics to preserve readable positional information, though readings can still be imperfect.

Beyond morphogens, cell-to-cell communication adds robustness, as seen in developmental systems like fruit fly wing formation.

There are many morphogens at work; for example, at least 13 bone morphogenic proteins influence bone and cartilage formation, with more likely undiscovered in complex organs like the brain.

Retinoic acid and Hox genes help establish body axes and positional identity, while later morphogens such as sonic hedgehog pattern the nervous system and limbs.