Asymmetric division of Drosophila male germline stem cell shows asymmetric histone distribution - PubMed (original) (raw)

Asymmetric division of Drosophila male germline stem cell shows asymmetric histone distribution

Vuong Tran et al. Science. 2012.

Abstract

Stem cells can self-renew and generate differentiating daughter cells. It is not known whether these cells maintain their epigenetic information during asymmetric division. Using a dual-color method to differentially label "old" versus "new" histones in Drosophila male germline stem cells (GSCs), we show that preexisting canonical H3, but not variant H3.3, histones are selectively segregated to the GSC, whereas newly synthesized histones incorporated during DNA replication are enriched in the differentiating daughter cell. The asymmetric histone distribution occurs in GSCs but not in symmetrically dividing progenitor cells. Furthermore, if GSCs are genetically manipulated to divide symmetrically, this asymmetric mode is lost. This work suggests that stem cells retain preexisting canonical histones during asymmetric cell divisions, probably as a mechanism to maintain their unique molecular properties.

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Figures

Figure 1

Figure 1. Experimental design and potential results

(A) A diagram of the GSC niche. HUB-hub cells, CySC- cyst progenitor/somatic stem cell. (B) Immunofluorescent image of the niche: HUB (anti-Fas III, red, asterisk), GSC-GB pair expressing H3-GFP (green, dotted outline) connected by a spectrosome (anti-α-Spectrin, red, arrow). (C) The UASp-FRT-histone-GFP-PolyA-FRT-histone-mKO-PolyA transgene. UAS:

u

pstream

a

ctivating

s

equence;

F

RT: FLP (flippase)

r

ecombination

t

arget; histone: H3, H2B, or histone variant H3.3. nanos-Gal4: a germline-specific driver. hs-FLP: the yeast FLP recombinase controlled by the

h

eat

s

hock (hs) promoter. (D–E) Two potential results: for simplicity, only one GSC-GB pair is shown, and each entire cell is colored according to histone fluorescence.

Figure 2

Figure 2. H3 is asymmetrically segregated during the second GSC division after heat shock

(A) Heat shock regime. H3 is distributed asymmetrically in GSC vs. GB (B-B”) but symmetrically in two-cell spermatogonia (C-C”). (D-D”) H3.3 is distributed symmetrically in GSC vs. GB. H3 distribution pattern in GSCs: (E-E”) G2 phase, (F-F”) anaphase, (G-G”) telophase. Scale: 5μm. Asterisk: HUB (anti-FasIII); arrow: spectrosome (anti-α spectrin). (H) Quantification of GFP and mKO fluorescence intensity ratio (Table S2). H3 GSC/GB GFP ratio > 1 (* P<10−4), GSC/GB mKO ratio < 1 (* P<10−4), _N_=15. H3 two-cell spermatogonial (SG) SG1/SG2 GFP ratio (# P=0.103) and mKO ratio (# P=0.684) insignificantly different from 1, _N_=16. H3.3 GSC/GB GFP ratio (# P=0.513) and mKO ratio (# P=0.532) insignificantly different from 1, _N_=12. Error bars: S.E. P-value: one-sample t-test.

Figure 3

Figure 3. H3 is asymmetrically distributed after the first GSC division after heat shock

(A) Heat shock regime. H3 is distributed asymmetrically in GSC vs. GB (B-B”) but symmetrically in two-cell spermatogonia (C-C”). (D-D”) H3.3 is distributed symmetrically in GSC vs. GB. (E-E”) A telophase GSC. Scale: 5μm. Asterisk: HUB (anti-FasIII); arrow: spectrosome (anti-α spectrin). (F) Quantification of GFP and mKO fluorescence intensity ratio (Table S4). H3 GSC/GB GFP ratio > 1 (* P< 10−4), GSC/GB mKO ratio < 1 (* P< 10−4), _N_=12. H3 two-cell spermatogonial (SG) SG1/SG2 GFP ratio (# P=0.225) and mKO ratio (# P=0.365) insignificantly different from 1, _N_=11. H3.3 GSC/GB GFP ratio (# P=0.970) and mKO ratio (# P=0.594) insignificantly different from 1, _N_=13. Error bars: S.E. P-value: one-sample t-test.

Figure 4

Figure 4. Loss of asymmetric H3 distribution pattern upon overexpression of upd

(A-A”) H3-GFP (A') and H3-mKO (A”) in nanos-Gal4; UAS-upd testis. Asterisk: HUB (anti-FasIII).

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