Notes on X-linked insertions of heat shock-FLP constructs
Updated December 5, 2013
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The Bloomington Stock Center has many stocks containing an X-linked insertion of a construct expressing FLP recombinase upon heat shock. To our knowledge, all of these insertions behave as one would expect and catalyze recombination between FRT sites. Nevertheless, there is some doubt regarding the identities of constructs and insertions in some stocks. This will not matter to most stock users, but the following presents our best understanding of this confusing situation.

Three constructs express FLP under control of an Hsp70 promoter. P{hsFLP} was described in Golic and Lindquist (1989) and P{hsp70-flp} was described in Struhl and Basler (1993). The two constructs seem similar in most respects. Golic and colleagues later replaced sequences flanking the 3' end of FLP in P{hsFLP} to create P{70FLP} with higher FLP recombinase expression.

An X-linked insertion of P{hsFLP} called P{hsFLP}1 was isolated and is still in common use. Stocks 6 and 7 were the first P{hsFLP}1 stocks at Bloomington. Later, Chou and Perrimon (1996) mobilized the autosomal P{hsFLP} insertion P{hsFLP}38 to isolate the new X-linked insertions P{hsFLP}12 and P{hsFLP}22 with higher FLP recombinase activity. Stocks of both insertions were sent to Bloomington. The P{hsFLP}22 stock (#1970) was lost in 2002. Stock 1929 is the original P{hsFLP}12 stock. An X-linked insertion of P{hsp70-flp} called P{hsp70-flp}1 was isolated, but we have never knowingly distributed a stock with it.

We are not 100% certain which insertion is present in many stocks. Many stocks arrived with a generic "hsFLP" genotype. We have listed most of these insertions as P{hsFLP}12, because it appears to be the most widely used insertion. Other stocks arrived with the insertion identified as "122". We suspect that "122" is P{hsFLP}12 in most stocks and have listed it that way in genotypes.

It is our impression that few X-linked heat shock-FLP insertions can be traced back with confidence to their origins, so we recommend that you characterize insertions molecularly if your goal is to make detailed comparisons. For many experiments, maximal FLP recombinase activity may not be necessary. For example, hundreds of FRT-derived deletions and duplications have been isolated here using P{hsFLP}1, which is reported to be the least efficient insertion.

No similar ambiguity surrounds P{70FLP} insertions or autosomal P{hsFLP} insertions in Bloomington stocks.