Worm Breeder's Gazette 10(2): 82

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lin-12 is Required in the Somatic Gonad for Germ Line Development

Geraldine Seydoux and Iva Greenwald

Figure 1

lin-12(0) hermaphrodites are essentially sterile.  As reported in 
the last edition of the Gazette, Tim Schedl first recognized that, in 
lin-12(0) hermaphrodites, the proximal germ cells do not enter meiosis 
but seem to continue to proliferate in the mitotic cycle, like the 
distal germ cells (see Figure), although gametes are present in the 
loop region.  We were interested in ascertaining whether lin-12 is 
required in the somatic gonad or in the germ line for proper germ line 
development.  Mosaic hermaphrodites obtained from the strain qDp3: 
65) 51) 41) 
were useful in distinguishing between these two possibilities.  [qDp3 (
Austin and Kimble, 1987) complements ncl-1, 
41) is a null allele of lin-
12.]  Five mosaics were obtained in which half of the gonad ( either 
the Z1 or the Z4 descendants) was Ncl- and therefore presumably lin-12(
0).  The presence of the Dp in the germ line was ascertained by 
looking for WT animals among the progeny of the mosaic hermaphrodite.  
In 5/5 mosaics, the half of the gonad not expressing lin-12 exhibited 
the lin-12(0) defect in the germ line, while the other wild-type half 
contained a normally differentiated germ line (see Figure); all 
mosaics produced some wild-type progeny.  These results are consistent 
with lin-12 function being required in the somatic gonad for wild-type 
development of the germ line.  (Our previous tentative inference of a 
requirement for lin-12(+) in the germ line was based on a mosaic 
phenotypic class that is also consistent with the interpretation 
presented here.) One possibility is that lin-12(0) animals have 
another, as yet unidentified, cell fate transformation in the gonad.  
This transformation would create a cell in the proximal part of the 
gonad that can promote mitosis in the germ line, a role normally 
associated only with the distal tip cell.  Another possibility is that 
lin-12 plays a more direct role in germ line development.  We hope to 
distinguish between these possibilities by laser ablation experiments.

Figure 1