Worm Breeder's Gazette 9(2): 42

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Tc1 Transposition Occurs in Both Germlines

D. Moerman

Figure 1

I have been attempting to determine if transposition occurs in both 
the oocyte and sperm lines, and if it does to compare the relative 
rates of movement in these two tissues.  To do this I have placed the 
following mutant construct, [See Figure 1], from strain CB3640 (kindly 
provided by Jonathan Hodgkin) in a mixed Bristol/Bergerac background.  
This male/female strain can be continuously propagated by crossing.  
The key to the analysis is that fem-1 and tra-3 are on chromosome IV 
and flank unc-22.  By picking single spontaneous males that twitch in 
nicotine, mating them to unc-5 tra-3 females and 
scoring in the next generation whether males or females twitch, it is 
possible to determine in which germline the transposition event 
occurred.  If the male progeny twitch in nicotine the unc-22 gene on 
the tra-3 chromosome must have been hit by Tc1 because this chromosome 
determines maleness.  This means that the original transposition event 
must have occurred in the sperm line since this chromosome can only 
come from the father.  On the other hand, if the female progeny twitch 
in nicotine then the unc-22 gene on the unc-5 tra-
3 chromosome must have been hit by TC1.  In this case the original 
transposition event must have occurred in the oocyte line since this 
chromosome is inherited from the mother.  In principal, this 
experiment is analogous to the Drosophila attached X mating scheme.
The data: The strain constructed has a rather low activity which is 
useful to insure independent events but means that I have a small 
number of positive events.  Only males which came from plates with no 
other twitching worms were analyzed to insure that I was monitoring 
the initial event.  To date I have analyzed 10 events; 4 occurred in 
the sperm line, 4 occurred in the oocyte line and 2 are indeterminate. 
These latter two events are puzzling because in the test cross male 
and female progeny twitched in nicotine.  I do not have an explanation 
for this observation although the time during development that 
transposition occurred, or recombination are two possibilities that 
need to be explored.  I think the present data is sufficient to 
conclude that transposition occurs in both germlines.  Taking into 
consideration the low numbers I would also suggest that the oocyte and 
sperm lines are not markedly different in their transpositional 

Figure 1