Abrams, Tan, Li
, et al
. eLife 2021;10:e65092. DOI: https://doi.org/10.7554/eLife.65092
1 of 25
A conserved strategy for inducing
appendage regeneration in moon
jellyfish,
Drosophila
, and mice
Michael J Abrams
1†‡§#¶
, Fayth Hui Tan
1†
, Yutian Li
1†
, Ty Basinger
1
, Martin L Heithe
1
,
Anish Sarma
1
, Iris T Lee
1
, Zevin J Condiotte
1
, Misha Raffiee
1‡§#¶
, John O Dabiri
2
,
David A Gold
1‡§#¶
, Lea Goentoro
1
*
1
Division of Biology and Biological Engineering, California Institute of Technology,
Pasadena, United States;
2
Graduate Aerospace Laboratories and Mechanical
Engineering, California Institute of Technology, Pasadena, United States
Abstract
Can limb regeneration be induced? Few have pursued this question, and an evolu-
tionarily conserved strategy has yet to emerge. This study reports a strategy for inducing regener
-
ative response in appendages, which works across three species that span the animal phylogeny.
In Cnidaria, the frequency of appendage regeneration in the moon jellyfish
Aurelia
was increased
by feeding with the amino acid L-
leucine and the growth hormone insulin. In insects, the same
strategy induced tibia regeneration in adult
Drosophila
. Finally, in mammals, L-
leucine and sucrose
administration induced digit regeneration in adult mice, including dramatically from mid-
phalangeal
amputation. The conserved effect of L-
leucine and insulin/sugar suggests a key role for energetic
parameters in regeneration induction. The simplicity by which nutrient supplementation can induce
appendage regeneration provides a testable hypothesis across animals.
Editor's evaluation
This paper shows that simple nutritional interventions such as L-
leucine, insulin or sucrose can trigger
appendage regeneration in three species that do not regenerate appendage in normal conditions,
the Aurelia jellyfish,
Drosophila
flies and mice. The results are stunning and provide novel model
systems to induce appendage regeneration in animals and to study the mechanisms underlying
regeneration.
Introduction
In contrast to humans’ poor ability to regenerate, the animal world is filled with seemingly Homeric
tales: a creature that regrows when halved or a whole animal growing from a small body piece. Two
views have historically prevailed as to why some animals regenerate better than others (
Goss, 1992
).
Some biologists, including Charles Darwin and August Weismann, hold that regeneration is an adaptive
property of a specific organ (
Polezhaev, 1972
). For instance, some lobsters may evolve the ability to
regenerate claws because they often lose them in fights and food foraging. Other biologists, including
Thomas Morgan, hold that regeneration is not an evolved trait of a particular organ, but inherent in all
organisms (
Morgan, 1901
). Regeneration evolving for a particular organ versus regeneration being
organismally inherent is an important distinction, as the latter suggests that the lack of regeneration
is not due to the trait never having evolved, but rather due to inactivation—and may therefore be
induced. In support of Morgan’s view, studies in past decades have converged on one striking insight:
many animal phyla have at least one or more species that regenerate body parts (
Sánchez Alvarado,
RESEARCH ARTICLE
*For correspondence:
goentoro@caltech.edu
†
These authors contributed
equally to this work
Present address:
‡
Department
of Molecular and Cell Biology,
University of California, Berkeley,
Berkeley, United States;
§
Department of Bioengineering,
Stanford University, Stanford,
United States;
#
Department
of Biology and Allied Health
Sciences, Bloomsburg University,
Pennsylvania, United States;
¶
Department of Earth and
Planetary Sciences, University of
California, California, California,
United States
Competing interest:
See page
21
Funding:
See page 21
Preprinted:
22 November 2020
Received:
22 November 2020
Accepted:
22 November 2021
Published:
07 December 2021
Reviewing Editor:
Virginie
Courtier- Orgogozo, Université
Paris-
Diderot CNRS, France
Copyright Abrams
et al
. This
article is distributed under the
terms of the Creative Commons
Attribution License, which
permits unrestricted use and
redistribution provided that the
original author and source are
credited.
Research article
Evolutionary Biology | Stem Cells and Regenerative Medicine
Abrams, Tan, Li
, et al
. eLife 2021;10:e65092. DOI: https://doi.org/10.7554/eLife.65092
2 of 25
2000
;
Bely and Nyberg, 2010
). Further, even in poorly regenerative lineages, many embryonic and
larval stages can regenerate. In regenerating animals, conserved molecular events (e.g.,
Cary et al.,
2019
,
Kawakami et al., 2006
) and regeneration-
responsive enhancers (
Wang et al., 2020
) were
identified. Although the hypothesis of convergent evolution cannot be fully excluded (e.g.,
Lai and
Aboobaker, 2018
), these findings begin to build the case that the ability to regenerate may be ances-
tral (
Sánchez Alvarado, 2000
;
Bely and Nyberg, 2010
). Regeneration being possibly ancestral begs
the question: is there a conserved mechanism to activate regenerative state?
This study explored how, and whether, limbs can be made to regenerate in animals that do not
normally show limb regeneration. In adult frogs, studies from the early 20th century and few recent
ones have induced various degrees of outgrowth in the limb using strategies including repeated
trauma, electrical stimulation, local progesterone delivery, progenitor cell implantation, and Wnt acti-
vation (
Carlson, 2007
;
Lin et al., 2013
;
Kawakami et al., 2006
;
Herrera-
Rincon et al., 2018
). Wnt
activation restored limb development in chick embryos (
Kawakami et al., 2006
), but there are no
reports of postnatal regeneration induction. In salamanders, a wound site that normally just heals can
be induced to grow a limb by supplying nerve connection and skin graft from the contralateral limb
(
Endo et al., 2004
), or by delivery of Fgf2, 8, and Bmp2 to the wound site followed by retinoic acid
(
Vieira et al., 2019
). In neonatal and adult mouse digits, a model for exploring limb regeneration
in mammals, bone outgrowth, or joint-
like structure can be induced via local implantation of Bmp2
(bone) or Bmp9 (joint;
Yu et al., 2019
). Thus far, different strategies gain tractions in different species,
and a common denominator appears elusive.
However, across animal phylogeny, some physiological features show interesting correlation with
regenerative ability (
Hariharan et al., 2016
;
Vivien et al., 2016
;
Sousounis et al., 2014
). First, regen-
eration especially in vertebrates tends to decrease with age, with juveniles and larvae more likely to
regenerate than adults. For instance, the mammalian heart rapidly loses the ability to regenerate after
birth and anurans cease to regenerate limbs upon metamorphosis. Second, animals that continue
to grow throughout life tend to also regenerate. For instance, most annelids continue adding body
eLife digest
The ability of animals to replace damaged or lost tissue (or ‘regenerate’) is a sliding
scale, with some animals able to regenerate whole limbs, while others can only scar. But why some
animals can regenerate while others have more limited capabilities has puzzled the scientific commu-
nity for many years. The likes of Charles Darwin and August Weismann suggested regeneration only
evolves in a particular organ. In contrast, Thomas Morgan suggested that all animals are equipped
with the tools to regenerate but differ in whether they are able to activate these processes. If the
latter were true, it could be possible to ‘switch on’ regeneration.
Animals that keep growing throughout their life and do not regulate their body temperatures
are more likely to be able to regenerate. But what do growth and temperature regulation have in
common? Both are highly energy-
intensive, with temperature regulation potentially diverting energy
from other processes. A question therefore presents itself: could limb regeneration be switched on
by supplying animals with more energy, either in the form of nutrients like sugars or amino acids, or
by giving them growth hormones such as insulin?
Abrams, Tan, Li et al. tested this hypothesis by amputating the limbs of jellyfish, flies and mice, and
then supplementing their diet with sucrose (a sugar), leucine (an amino acid) and/or insulin for eight
weeks while they healed. Typically, jellyfish rearrange their remaining arms when one is lost, while fruit
flies are not known to regenerate limbs. House mice are usually only able to regenerate the very tip of
an amputated digit. But in Abrams, Tan, Li et al.’s experiments, leucine and insulin supplements stim-
ulated limb regeneration in jellyfish and adult fruit flies, and leucine and sucrose supplements allowed
mice to regenerate digits from below the second knuckle. Although regeneration was not observed
in all animals, these results demonstrate that regeneration can be induced, and that it can be done
relatively easily, by feeding animals extra sugar and amino acids.
These findings highlight increasing the energy supplies of different animals by manipulating their
diets while they are healing from an amputated limb can aid in regeneration. This could in the future
pave the way for new therapeutic approaches to tissue and organ regeneration.