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Thanks for replies on mnC1

Jeffrey Yuan yuan at PHOENIX.PRINCETON.EDU
Thu Jul 27 13:30:49 EST 1995

Wow!  The response to my query on mnC1 was impressive.  I would like to thank 
everyone who took time to reply.  For those of you who missed the original 
posting, I wanted to know if the crossover suppressor mnC1 can breakdown, since 
I have begun to notice motile dpy hermaphodites and males after constructing the
following strain: mnDf67 unc4/mnC1(dpy10 unc52); him5(e1490).

The replies I received fall basically into three groups.  One group alerted me 
to the presence of him-5 induced dpy triplo-x animals, which is something that I
definitely see.  The other group alerted me to the fact that mnC1 does breakdown
at a certain frequency. Finally there was a third group that has other useful 
information on other crossover suppressors and mnC1 in particular. 

Here are the replies:

Raffi Aroian writes that  "Yes!  Mnc1 does have problems when introduced with 
him-5.  I saw this years ago when working on let-23.  In particular there are
two problems: one is recombinants (as you have seen) and the other is that one 
can get triplo chromosomes.  Even with Df strains in the region I quickly 
abandoned using mnC1 with him-5 and switched  to male strains. mnDf67 can be 
maintained as a balanced male strain (het males are fertile) starting with heat 
shock males."

Mike Finney, Barth Grant, and Meera Sundaram all warned me about triplo-x 
animals due to him-5.

Joel Rothman writes that "We recently got SP781 (mnC1 / unc-4 mnDf97) from the 
CGC and found lots of fertile Dpys on the plates.  We're sorting it out at the 
moment, but it looks a lot like an mnC1 breakdown.  Please let me know what 
other responses you get."

Leon Avery writes that "Yes, mnC1 will occasionally break down.  I think there's
a frequency reported in the orginal paper."

Jill Bettinger says that "i don't have any frequency numbers for you, but mnC1 
does occasionally break down. i use it regularly, and i have observed motile 
dpys that are (i think) fertile. generally, i chase the recombinant chromosome 
away by cloning animals and looking for the classic dpyuncs. people in bob 
herman's lab would be able to give you a better idea about how often this 
happens; i can only tell you it isn't very frequent. "

Mark Edgley provided this. "I worked with mnC1 a bit at the CGC, but never put 
him-5 into it.  I did notice occasional Dpy or Unc recombinants,
but they were invariably sterile.  You might ask Bob Herman
directly if he ever saw anything different.
Are you sure the Dpy animals you're seeing are real dpy-10's
and not X dosage Dpys of some sort?"

Andras Fodor mentioned that szT1 breaks down.  Similarly, Dave Reiner observed 
that eT1 also breaks down.

Lew Jacobson writes that "From some experiments we did more than 5 years ago, we
concluded that mnC1 is probably an inversion. We saw what could be best 
interpreted as recombination events inside mnC1 giving rise to deletions with 
fairly consistent endpoints.  Don't know if this helps."

And Patty Kuwabara writes that "I've seen mnC1 breakdown in strains several 
times. The animals generated from such a breakdown, at least in my hands, are 
not wild-type in appearance.  Breakdown usually occurs when making transgenics 
or when generating new strains.  Otherwise, mnC1 appears to remain a good
balancerfor maintaining stocks."

Thanks for all those who took time out to reply. 


Jeff Yuan


*  Jeffrey Yuan                                                          *
*  Department of Molecular Biology                                       *
*  Lewis Thomas Laboratory                                               *
*  Princeton University                FAX: 609-258-3980                 *
*  Washington Road                   Phone: 609-258-5939                 *
*  Princeton, NJ  08544              email: yuan at phoenix.princeton.edu   *

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