Quantitative dissection of size memory during zebrafish appendage regeneration

ABSTRACT
The ability of mammals to regenerate injured appendages is limited to healing bone fractures and regenerating
digit tips. For any future therapies to be useful they must pattern regrowth so that it restores tissue size and
function and avoids hypertrophy and dysmorphology. In contrast to mammals, zebrafish regenerate entire
appendages following an injury, such as amputation. Notably, regenerated fins reproduce the original size,
shape, and function of the injured appendage. While previous work has identified molecules and cellular events
required for promoting zebrafish fin regeneration, we still do not fully understand how cells within a regenerating
appendage encode size memory or how cells dynamically monitor the progression of regenerative outgrowth
to ensure accurate tissue size. This is partly due to the difficulty of rigorously documenting cellular events, such
as signaling levels, in vivo in complex tissues at single-cell resolution. This proposal will overcome these
difficulties by combining quantitative live imaging approaches, computational analysis, and theoretical
modeling to map cell signaling activity with single cell resolution. Specifically, Aim 1 will dissect how the initial
conditions encoding size memory are established for fin rays of different lengths. Aim 2 will uncover how size
memory is processed in fibroblast tissue, which comprises connective tissue-secreting cells that lie inside and
between bony hemirays. Aim 2 will also test the hypothesis that size memory is differentially regulated in
fibroblasts and osteoblasts (bone-matrix secreting cells) by distinct upstream Fibroblast Growth Factor (Fgf)
ligand expression. The research outlined here will form the intellectual basis of my own independent research
program. Together with my advisors, Dr. Stefano Di Talia and Dr. Ken Poss, I have developed a training plan
that will enable me to master skills in theoretical approaches and transgenic zebrafish generation as well as
gain hands-on lab management experience during the K99 award phase. Furthermore, I have established an
exceptional committee of advisors, including expert theorists and experimental biologists, who are committed
to helping me develop my independent research program. The research and training described here will
uniquely position me to apply this interdisciplinary, quantitative approach to additional signaling pathways, such
as Wnt, and other regenerating tissues, including the vasculature and the nervous system. Long-term, I will
lead my own research group in generating a wholistic understanding of how size memory is established and
dynamically processed during fin regeneration. I expect the insights gained from this research will inform the
development of regenerative therapies that promote tissue regrowth in humans without inducing pathogenic
overgrowth or dysmorphology.

Grant Number: 1K99HD119028-01
NIH Institute/Center: NIH
Principal Investigator: Ashley Baker