Fig. 3.

CED-1 from the muscle-type engulfing cell is adhesive to regenerating axons and mediates axon debris phagocytosis. a–f Regenerating ALM axons were adhered to muscles overexpressing CED-1. Representative images were taken in young adult stage 24 h after injury (a–e). Anterior is to the left; dorsal is up. Scale bar: 20 μm. a The ALM axon in wild-type animals expressing the Punc-54::mCherry transgene was not adhered to muscles. b The ALM axon in wild-type animals expressing the Punc-54::sax-7 transgene was not adhered to muscles. c–e ALM axons in wild-type animals expressing the Punc-54::ced-1 transgene were adhered to muscles. The dashed box area in (c) was blown up in (d). Red dots in (d) and (e) indicate regenerating axon endings at muscles and yellow asterisks in (e) mark muscle protrusions. f The percentages of regenerating ALM axons adhered to muscles. The N number represents the number of animals analyzed. Error bars represent SEP. Asterisks represent P < 0.001 by Z-test for two proportions. g Average length of regenerating ALM axons. The muscle-specific knockdown of ced-1 caused reduced axon regeneration. Axons were visualized using the zdIs4[Pmec-4::GFP] marker. ns indicates no significant difference. Error bars indicate SEM. **p < 0.01. P values were calculated using a Student’s t-Test. h Axon debris were labeled by the Pmec-4::GFP transgene and muscle protrusions were labeled by the Punc-54::ced-1::mRFP reporter. The green open arrowhead and the asterisk point to axon debris and the muscle protrusion, respectively. i Axon debris were labeled by the Pmec-4::myr::mCherry transgene and body wall muscles were labeled by the Punc-54::ced-1::GFP reporter. The white arrowhead points to a phagosome encircling axon debris. Images were taken in young adult stage 4 h after axotomy for axon debris (h and i). Scale bar: 10 μm. j and m CED-1::GFP-expressing vesicles in muscle cells. Early phagosomes (k) and late phagosomes (n) in muscle cells were labeled by the Rab-5::TagRFP and the Rab-7::TagRFP, respectively. l and o Superimposed images. Arrows indicate CED-1::GFP-expressing vesicles whereas arrowheads mark either Rab-5::TagRFP-positive halos (k) or Rab-7::TagRFP-positive halos (n). p The percentages of CED-1::GFP positive vesicles that are also positive for either Rab-5::TagRFP or Rab-7::TagRFP