Science - USA (2021-11-12)

domain of Patronin, but not the CKK domain
( 25 ), also prevents Patronin accumulation in
the pro-oocyte (fig. S6, C and D). Thus, Patronin
localization depends on its binding to MT minus
ends and on Dynein activity, suggesting that
Dynein transports Patronin bound to MT minus
ends toward the pro-oocyte.

Our observations led us to propose a four-

step model of cyst polarization and oocyte se-

lection (Fig. 4E). First, during cyst formation,

the asymmetric segregation of the fusome leads

to the one cell with more fusome material than

the rest. Second, in region 2a, Patronin is re-

cruited to the fusome by Shot. The cell with

the most fusome material therefore contains

more Patronin, leading to the stabilization of

moreMTminusendsinthiscellandaweakly

polarized MT network. Third, Patronin-bound

MTs in other cells of the cyst are then trans-

ported by Dynein along these MTs toward

their minus ends in the pro-oocyte. Fourth,

878 12 NOVEMBER 2021¥VOL 374 ISSUE 6569 science.orgSCIENCE

E

Step 1 Step 2 Step 3 Step 4

• Shot
  
  
  • Dynein
    
    
    • Patronin
    
    
    • MT
      
      
      • ncMTOC
        
        
        • Fusome
          
          
          • Oocyte
            determinant
          
          
          
          
        
        
        
        
      
      
      
      
    
    
    
    
  
  
  
  

Oocyte differentiation

D

A

Patronin-YFP

Region1 2a 2b 3 2a 2b

B

2a 2b

Patronin-YFP

C

Patronin-YFP Hts-Cherry

+colcemid

Hts-Cherry

Region1 2a 2b 3

Patronin-YFP

+colcemid

Patronin-YFP nlsRFP Patronin-YFP nlsRFP

Patronin-YFP nlsRFP Patronin-YFP nlsRFP^

WT shot

Region 1 2a 2b 3

Region 1 2a 2b (^3) Region 1 2a 2b 3
Region 1 2a 2b 3
Patronin-GFP
Patronin-GFP egalitarian
WT
1 2a 2b 3
Hts
Patronin
Hts
Patronin
Fig. 4. Patronin localization is defined by the fusome and by a positive
feedback loop of Dynein-mediated transport.(AandB) Patronin associates
with the fusome in an MT-dependent manner. Shown are untreated (A) or
colcemid-treated (B) live germaria expressing Patronin-YFP and Hts-Cherry.
Regions 2a and 2b are shown as close-ups. (C) Shot links Patronin to the
fusome. Shown are live germaria containing WT (left) andshotMUT (right)
cysts expressing Patronin-YFP either untreated (top) or treated with colcemid
(bottom). (D) Patronin localization depends on Dynein activity. Shown are WT
(top) andegalitarianMUT (bottom) live germaria expressing transgenic Patronin-
GFP. (E) Diagram showing the four steps in cyst polarization that lead to the
specification of the oocyte and its subsequent positioning at the posterior of the
cyst in region 3 (see text for details). Asterisk indicates the presumptive oocyte.
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