Date: Wed, 31 Jul 2002 18:00:36 -0500
From: Dominic Ebacher
Subject: re: FRT(18A) and Developmental Abnormalities

Dear Dr. Matthews:

My name is Dominic Ebacher and I am a graduate student in Grace Panganiban's 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