Figure 3. AMPs stay connected to surrounding muscles until reactivation.

(A) A dorso-lateral view of two hemisegments in mid-stage embryo showing lateral, dorso-lateral and dorsal AMPs (green) and embryonic muscles (blue). Two lateral AMPs (white and yellow arrows) send numerous filopodia to lateral muscle fibers. Note that one of the lateral AMPs (yellow arrow) extends along the segment border muscle (SBM). (B) A zoomed view of two lateral AMPs from the early second larval instar. The AMP indicated by the yellow arrow stays connected to the SBM and sends two long cellular extensions (yellow arrowheads) along the SBM. The second lateral AMP (white arrow) still produces filopodia (white arrowheads) linking it with the SBM and the LO1 muscle. The number of filopodia-based AMP-to-muscle connections is reduced compared to embryonic stages. Nuclei of AMPs (red) are revealed by anti-Twi staining. (C) A similar view of lateral AMPs from mid-second larval instar undergoing first cellular division. Note that the reactivated AMPs indicated by two white and two yellow arrows keep their extended shapes and filopodia-based connections (white and yellow arrowheads) to the SBM and LO1 muscles. (D) Proliferating lateral AMPs from third instar larva labeled with anti-Twist (red) to reveal their nuclei and anti-GFP (green) to reveal their shapes. The remaining cellular extension (yellow arrowhead) is still shown connecting one of lateral AMPs to the SBM muscle. The cells originating from the AMP connected to the LO1 muscle are aligned along this muscle (white arrowhead). Note that proliferating AMPs form clusters of tightly-associated cells. Scale bars in (A): 12 microns; in (B, C): 25 microns; in (D): 36 microns.

DOI: http://dx.doi.org/10.7554/eLife.08497.012

Figure 3—figure supplement 1. Larval AMPs adapt their shapes and keep associated to rapidly growing muscles.

(A) Flat preparation of first-instar M6gapGFP larvae stained for GFP (green) to reveal AMPs and phalloidin (magenta) to label muscles. Notice the elongated shapes of AMPs and persisting interconnections (arrowhead). Arrows indicate two lateral AMPs. (B) At second larval instar AMPs continue to elongate and adapt their shapes to keep connected with growing muscles. Arrows point to lateral AMPs among which the anterior one has already divided. (C) Nutrient restricted conditions prevent reactivation of AMPs. Arrows point to two lateral AMPs, which keep quiescent in third-instar larvae grown with nutrient restriction. Note that ~16 lateral AMP cells are detected in normal nutrient condition at this stage. Scale bars in (A, C): 15 microns; in (B): 30 microns.

DOI: http://dx.doi.org/10.7554/eLife.08497.013