Date: Wed, 31 Jul 2002 18:00:36 -0500
From: Dominic Ebacher <djebacher%students.wisc.edu>
Subject: re: FRT(18A) and Developmental Abnormalities

Dear Dr. Matthews:

My name is Dominic Ebacher and I am a graduate student in Grace Panganiban¹s
lab. I have gathered some information that I thought might be worthy of your attention
and perhaps a note in Flybase. While conducting crosses recently, I encountered
anomalous results with flies of genotype FRT(18A); eyFLP. Subsequent test crosses
revealed that in the presence of continuous FLPase, FRT(18A) is >75% lethal and
100% of the escapers have severe eye and head defects. Test crosses with other
FRT(18A) chromosomes and other FLPase stocks indicate that these phenotypes
are due to the FRT(18A) chromosome . I now have tested eyFLPase stocks with
insertions on either the second or third chromosome. All yield the same results with
FRT(18A). None are lethal with FRT(19A) stocks. The lethality and developmental
abnormalities are observed with both male and female flies carrying an FRT(18A)
chromosome, so the defects are not due to inter-chromosomal recombination. I
therefore suspect that the original FRT(18A) chromosome has an aberration (perhaps
another FRT site near the one at 18A) and that this has been transmitted to
recombinant chromosomes carrying FRT(18A). I further suspect that recombination
between the two FRT sites deletes essential genes, leading to cell lethality and head
defects. Consistent with my results, Seth Blair has been able to disrupt wing disc
development using flies carrying FRT(18A) and ap-GAL4, a continuous source of
FLPase in the wing. Thus FRT(18A) probably is cell lethal in the presence of
continuous FLPase. In light of this, we recommend that people use the FRT(18A)
chromosome only with transient (e.g. heat shock-inducible) FLPase, and that they
use FRT(19A) whenever feasible.

Yours Sincerely

Dominic Ebacher