Research Article

Glia relay differentiation cues to coordinate neuronal development in Drosophila

See allHide authors and affiliations

Science  01 Sep 2017:
Vol. 357, Issue 6354, pp. 886-891
DOI: 10.1126/science.aan3174
  • Fig. 1 Photoreceptors do not communicate directly with lamina precursors through EGF.

    (A) Schematic of lamina development in the optic lobes, which is coupled to photoreceptor development in the eye disc. Hh from photoreceptors drives lamina precursor (purple) birth and assembly into columns. Photoreceptor-EGF is required for precursor differentiation into neurons (yellow). Columns consist of 6 or 7 precursors, which differentiate in an invariant spatiotemporal pattern (yellow). (B, B′, and B′′) A horizontal view of an early pupal (10 to 15 hours APF) eye disc and optic lobe showing photoreceptor axons marked by horseradish peroxidase (HRP) (cyan). In the optic lobe, lamina precursors express Dac (magenta) and differentiated photoreceptors, and neurons express Elav (yellow). Lamina cell bodies (magenta) are organized into columns that associate with photoreceptor axons. Wrapping (wr.) glia, marked by membrane-targeted GFP (white) driven by a wrapping glia–specific Gal4, extended processes through the optic stalk and into the lamina, where they encapsulate lamina cells and photoreceptors progressively [inset in (B′′); arrowheads mark location of photoreceptors between glial processes and lamina cells]. (C, C′, and C′′) Expressing HtlDN in wrapping glia disrupted glial process infiltration into the lamina. Only cells immediately below glial processes differentiated [arrowhead in (C′′)]. (D and D′) Lamina-specific Gal4 driving GFP showed normal lamina neuron differentiation. (E) Lamina-specific EGFRDN and P35 coexpression did not affect neuronal differentiation. (F) Lamina-specific AopACT and P35 coexpression led to loss of differentiated neurons (dashed bracket). (G) Lamina-specific MAPKACT expression led to premature Elav expression in columns. (H) Quantification of (D) to (G) as a percentage of differentiated cells in the six youngest lamina columns. Asterisks indicate significance with Mann-Whitney U test; P < 0.01; no. of optic lobes examined indicated in parentheses. Scale bar, 10 μm.

  • Fig. 2 L1 to L4 differentiation requires photoreceptor-induced EGFR signaling in wrapping glia.

    (A to C) Eye discs with wrapping glia marked by the panglial nuclear marker Repo (magenta) and dpMAPK (yellow) in (A) rho3–/+ and (B) rho3−/− animals, quantified in (C). P < 0.001; Mann-Whitney U test; no. of discs indicated in parentheses. (D to G) Optic lobes stained for Elav (yellow), Dac (magenta), HRP (cyan), and GFP (white). (D) A control wr.glia>GFP lamina. (E) When wrapping glia express EGFRDN, only presumptive L5s differentiated (arrow head). (F) In a rho3−/− animal, there was only a late differentiating presumptive L5 (see also fig. S1, C to G). (G) When wrapping glia express EGFRACT and GFP in a rho3−/− background, the L1 to L4 front of differentiation is restored (bracket). (H and I) Developmentally expressed subtype-specific markers used in combination to identify neuronal subtypes (16): Sloppy paired 2 (Slp2) alone marks L2 and L3; Slp2 and Seven up (Svp) together mark L1, Brain-specific homeobox (Bsh) alone marks L4, and Slp2 and Bsh together mark L5 (dashed line indicates lamina plexus). (H) In a control rho3–/+ brain and (I) when wrapping glia drive EGFRACT (and GFP; not shown) in a rho3−/− background, all cell types were recovered. (J) Quantification of (D) to (G) as a percentage of differentiated cells in the six youngest lamina columns. Asterisks indicate significance with Mann-Whitney U test, P < 0.01; no. of optic lobes examined indicated in parentheses. Scale bar, 10 μm.

  • Fig. 3 Wrapping glial insulin-like peptides induce lamina neuronal differentiation.

    (A) Normal lamina neuronal differentiation in a control. (B) A chico−/− brain lacked L1 to L4 differentiation (dashed bracket). (C) Ilp6-Gal4 and (D) Ilp7-Gal4 drove expression of GFP (membrane or cytoplasmic, respectively) in wrapping glia and their extensions into the optic stalk (yellow arrows). (E) A rho3−/− lamina. (F) A rho3−/− animal with wrapping glia expressing Ilp6 showed L1 to L4 differentiation (bracket). (G) A rho3−/− animal with the lamina expressing InRACT showed neuronal differentiation (bracket). Elav (yellow), Dac (magenta), HRP (cyan) and GFP (white). (H) Quantification of (F) and (G) as a percentage of differentiated cells in the six youngest lamina columns. Asterisks indicate significance with Mann-Whitney U test, P < 0.01; no. of optic lobes examined indicated in parentheses. Scale bar, 10 μm.

  • Fig. 4 The signaling relay may serve to delay differentiation to ensure consistent column assembly.

    (A to D) Early pupal (stages indicated) eye-optic lobe complexes stained for Elav (yellow), Dac (magenta), HRP (cyan), and [(C) and (D)] GFP (white). Cyan dashed line marks the youngest photoreceptors. (A) Control. (B) rho3−/−. (C) An early-onset panphotoreceptor Gal4 driving GFP and Ilp6 in a rho3−/− background. Differentiation was widespread and initiated in the youngest column (arrowhead), which contained about four lamina precursors. (D and E) A late-onset panphotoreceptor Gal4 driving GFP and Ilp6 in a rho3−/− background. (D) At ~10 hours APF, differentiation initiated only in old columns (arrowheads), but columns assembled 6 or 7 lamina precursors/column. (E) At ~15 hours APF, GFP and Ilp6 were expressed in all photoreceptors. Differentiation was widespread but variable because some columns contained more differentiated neurons than their older neighbors (arrowhead). Scale bar, 10 μm.

  • Fig. 5 A signaling relay from photoreceptors to glia to lamina precursors instructs lamina differentiation.

    Model: Photoreceptors secrete EGF and FGF, which activate EGFR and FGFR, respectively, in wrapping glia. EGFR activation is required for glial expression of Ilps, which activate InR and MAPK in lamina precursors leading to L1 to L4 differentiation. FGFR signaling regulates glia morphogenesis and process extension into the brain (3) and therefore indirectly regulates the timing and patterning of L1 to L4 differentiation.

Supplementary Materials

  • Glia relay differentiation cues to coordinate neuronal development in Drosophila

    Vilaiwan M. Fernandes, Zhenqing Chen, Anthony M. Rossi, Jaqueline Zipfel, Claude Desplan

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

    Download Supplement
    • Materials and Methods
    • Supplementary Text
    • Figs. S1 to S4
    • Tables S1 and S2
    • References

    Images, Video, and Other Media

    Movie S1
    Z-stack of a control eye-optic lobe complex in which a wrapping glia-specific Gal4 drives expression of membrane targeted GFP. Wrapping glia are found basally in the eye disc and wrap PRs coherently in the optic stalk and into the optic lobe. (GFP in white; Dac in magenta; HRP in cyan). (Scale bar = 10μm).
    Movie S2
    A Z-stack of an eye-optic lobe complex in which wrapping glia express membrane targeted GFP and 2 copies of HtlDN. As was previously shown, wrapping glia morphogenesis is perturbed such that large regions where PR axons are not wrapped by glia and the optic stalk appears thinner. (GFP in white; Dac in magenta; HRP in cyan). (Scale bar = 10μm)
    Movie S3
    A Z-stack of an eye-optic lobe complex in which wrapping glia express membrane targeted GFP and EGFRDN. Wrapping glial still wrap PRs coherently in the optic stalk and into the optic lobe and their overall morphology appears normal. (GFP in white; Dac in magenta; HRP in cyan). (Scale bar = 10μm).

Stay Connected to Science

Navigate This Article