Figure 1. | Neural stem cell-encoded temporal patterning delineates an early window of malignant susceptibility in Drosophila
Neural stem cell-encoded temporal patterning delineates an early window of malignant susceptibility in Drosophila
Aix Marseille Univ, CNRS, IBDM, France; Indiana University, United States; Institut de Génomique Fonctionnelle, France
Download figureOpen in new tabFigure 1. A subset of dNBs induced by Pros knock-down propagates malignant tumors in adults.
The scale bar in all images represents 30 μm. NBs and dNBs are always labeled using an anti-Mira antibody. Neurons are labelled using anti-Elav. (A) Schematic drawing representing a ventral view of the late larval (L3) and adult Drosophila CNS. Ventral nerve cord (VNC). NBs are represented as red circles. The poxn-GAL4 driver is active in six lateral NBs of the larval VNC (marked in green on the scheme). In poxn-GAL4, UAS-GFP larvae (poxn>GFP), GFP labels the six NBs (white arrows) and their recently generated progeny due to transient GAL4 and GFP perdurance. All NBs are absent in the adult VNC. (B) In poxn-GAL4, UAS-prosRNAi, UAS-GFP, UAS-dcr2 larvae (poxn>prosRNAi, GFP), six tumors of dNBs are generated. dNBs are represented on the scheme as green circles filled in red. A subset of dNBs persist and form small tumors in 1 day-old adult VNCs. (C) In 6 day-old adults, poxn>prosRNAi, GFP tumors cover the whole VNC and invade adjacent tissues such as the brain, and halteres (D) Mean tumor volumes quantified in wt poxn> GFP adult VNCs and in poxn>prosRNAi, GFP 1 and 6 day-old adult VNCs. No tumor is observed in wt adults. 1 day-old poxn>prosRNAi, GFP VNCs (n= 5 VNCs, m = 1.4x105, SEM = 6.3x104) and 6 day-old poxn>prosRNAi, GFP VNCs (n = 7 VNCs, m = 1.5x106, SEM = 1.8x105). p-value is 2.5x10-3. (E) poxn>prosRNAi, GFP tumors are almost exclusively composed of dNBs in late L3, and devoid of neurons (Elav). At around 20 hr after pupa formation, a brief pulse of neuronal differentiation in poxn>prosRNAi, GFP tumors is seen. GFP briefly labels recently differentiated Elav+ neurons due to transient GAL4 perdurance. In adults, persisting dNBs reconstitute malignant tumors.
Download figureOpen in new tabFigure 1—figure supplement 1. Progeny-to-NSC dedifferentiation and temporal progression in the developingcentral nervous system of Drosophila.
(A) Type-I and Type-II NBs in the larval central nervous system. Type-I NBs (large red circle) divide asymmetrically to self-renew and generate GMCs (medium red circle with nuclear Pros), which divide once to generate two neurons (small gray circles with nuclear Nerfin) or glia. Type-II NBs divide asymmetrically to self-renew and generate immature Intermediate Neural Precursors (imINPs, expressing Brat). imINPs maturate into INPs and undergo several rounds of asymmetric divisions to self-renew and generate GMCs (expressing nuclear Pros+). Each GMC divides once, giving birth to two differentiating neurons or glial cells. (B) During embryonic and larval development, each VNC NB sequentially expresses a series of transcription factors (Hunchback (Hb), Kruppel (Kr), Pdm1/2 (Pdm), Castor (Cas) and Seven-up (Svp)) inherited by the GMC. The various GMCs subsequently generate different types of neurons (differently colored circles), which identity is determined by their birth-order. NBs that are mutant for temporal factors, such as cas or svp, fail to progress further in the series and continuously generate the same type of neurons. Such NBs fail to exit the cell cycle during pupal stages and continue dividing during adulthood.
Download figureOpen in new tabFigure 1—figure supplement 2. poxn>prosRNAi larvae possess tumors in the VNC but not in the brain.
poxn-Gal4 expression (GFP staining) in the larval CNS is limited to six lateral NBs and their closed progeny in the VNC (1). Thus, removing pros by RNAi using poxn-Gal4 leads to the formation of six tumors in the VNC. poxn-GAL4 is not active in brain NBs, although being expressed in a small subset of neurons (2 and 3). Consequently, no tumors are generated in the brain. NBs are labeled with Mira in red, and the neurons are labeled with Elav in blue.
Download figureOpen in new tabFigure 1—figure supplement 3. L1/L2-induced MARCM pros-/- clones generate malignant tumors in adult.
(A) wt late L3 NBs express Mira and generate neurons labeled with anti-Elav. NBs are absent in adult VNCs. GFP+ pros-/- MARCM clones induced during early larval (L1/L2) development generate dNBs that form tumors that persist in adults and cover the VNC. (B) In late L3, GFP+ pros-/- MARCM clones induced during L1/L2 are almost exclusively composed of dNBs (Mira+) and are devoid of neurons (Elav-). At around 20 hr after pupa formation, a large number of dNBs differentiates into Elav+ neurons. In adults, persisting dNBs reconstitute malignant tumors. Yellow asterisk indicates axonal bundles induced by earlier neuronal differentiation of dNBs during metamorphosis.