Genetic and biophysical analysis of morphogen gradient formation - Principal Investigator: Schlissel, Gavin
Project summary
Animal development and physiology require regular communication among cell types embedded in tissues.
Cellular communication commonly relies on signaling proteins, which can transit the space between cells and
relay information across a wide range of spatial scales from nanometers to meters. Proper control of signaling
range is strictly necessary during animal development, and dysregulation of signaling range can result in a
spectrum of embryonic lethal conditions or developmental disorders.
The patterning gradient formed by a signaling protein reflects the signaling protein’s ability to travel
through the extracellular matrix, which is an amalgam of protein, sugar and lipids that organize cells in natural
tissues. Although signaling proteins are thought to diffuse from their source to their target, many proteins violate
the assumptions of free diffusion and instead show context-dependent differences in their signaling range. For
example, Sonic Hedgehog family developmental morphogens form signaling gradients over ~10µm in the testes,
~50µm in the developing neural tube or in adult hair follicles, and ~300µm in developing long bones. Notably,
tissues in which Sonic Hedgehog forms longer signaling gradients tend to express Scube family extracellular
matrix proteins, and Scube family proteins can dramatically extend Sonic Hedgehog signaling gradients in cell
culture.
I suspect that tissue-specific differences in signaling range might reflect direct regulation of Sonic
Hedgehog’s diffusion rate, and that regulated diffusion of Hedgehog might reflect a broadly used strategy to
control the size of signaling gradients in animals. To understand how morphogens and the extracellular matrix
interact to generate appropriately sized signaling gradients, I will measure variation in protein diffusion both
between diverse signaling proteins, and between distinct extracellular environments. I will apply this mechanistic
understanding to discover how biochemical features of signaling proteins and the extracellular matrix result in
size variation among signaling gradients as well as morphological variation among the anatomical features that
they pattern. To that end, I propose the following specific aims:
1) Understand how Scube family proteins modify hedgehog diffusion by tracking single particles of sonic
hedgehog diffusing through the extracellular matrix.
2) Discover which biochemical features of a signaling protein affect its diffusion rate through the
extracellular matrix by developing synthetic morphogens, in which diffusion can be uncoupled from
downstream signal transduction.
3) Identify extracellular matrix modifiers of protein diffusion that contribute to tissue- or organism-specific
signaling gradient size discrepancies by genetically simulating tissue-specific extracellular matrix
variation
K99/R00 Fellowship Application
October 2022
