Comment on 'A conserved strategy for inducing appendage regeneration in moon jellyfish, Drosophila, and mice'

Abstract

Abrams et al. report that a simple dietary supplement is sufficient to induce appendage regeneration in jellyfish, fruit flies, and mice (Abrams et al., 2021). This conclusion is surprising because it was previously thought that flies and mice lack the capacity for regeneration after injury. We replicated the Drosophila experiments of Abrams et al. but did not observe any instances of leg regeneration. We also conclude that the "white blob" observed at the amputation site by Abrams et al. consists of bacteria and is not regenerated tissue.

Keywords: D. melanogaster; fruit fly; limb; regeneration; regenerative medicine; stem cells.

Figure 1.. Tibia amputation in wild-type (Canton-S) Drosophila legs.

(A) The experimental protocol. We amputated one hind leg per fly, at the midpoint of the tibia. After three weeks on control food or treated food, legs were fixed and analyzed. (B–E) Bright-field images of a control leg (B), four examples of freshly cut legs (C), and five examples of legs after three weeks on control food (D) or treated food (E). Insets showed magnified views of the cut site. Scale bar in B is the same for other panels.

Figure 2.. Investigation of tissue identity in amputated legs.

Sensory neurons were labeled with ChAT-Gal4 >UAS GFP (A), muscles were labeled with phalloidin (B), and nuclei were labeled with DAPI (C) in uncut legs, freshly cut legs, and 3 weeks post-amputation with control food or treated food. Insets show magnified views of tissue within the femur and tibia. Scale bars in A are the same for all other panels except for insets in C.

Figure 3.. The white blob on amputated tibia stumps is most likely composed of bacteria, not regenerating fly tissue.

(A) Bright-field (left) and confocal images (right) of leg stumps stained with EdU (red) and DAPI (white) to test for cell proliferation. Tibia stumps did not incorporate EdU. The positive control, fly gut (B) did stain for EdU. (C) Three additional examples of DAPI staining and one example showing lack of phalloidin staining (D) in white blobs (n=12). Note that cells in (C) are smaller and more densely packed than fly leg hemocytes (E, green = Hml > GFP), fly leg bristle sensory neurons (F, green = 39A11 Gal4>GFP), fly leg muscle cells, larval leg imaginal disc cells (H), or fly food yeast (I). The nuclei in (C and D) are consistent with small, densely packed bacteria, such as those observed in fly excrement (J).