forever young: a gene facilitating the study of the third larval instar of D. melanogaster.

Czank, Andreas,¹ and Eric Kubli².  ¹Swissmedic, Erlachstr. 8, 3000 Berne 9, Switzerland, andreas.czank@swissmedic.ch;  ²Corresponding author, Institute for Zoology, University of Zurich, Winterthurerstr. 190, 8057  Zurich, Switzerland;  ekubli@zool.unizh.ch

In our study of the gene sarah (genetic symbol sra; synonym nebula, genetic symbol nla; publication in preparation), we discovered two alleles of the gene forever young (genetic symbol fey). When balanced over TM6B, Tb e, homozygous fey larvae are identifiable by their Tb⁺ phenotype. Tubby (Tb) causes short, thick individuals; the phenotype is visible in larvae, pupae and adults. fey¹ homozygotes, fey²/Df(3R)sbd (see below), and fey¹/fey² trans-heterozygotes develop to the third instar larvae.  Some eventually pupate. Homozygous fey² animals die at an earlier stage.

The fey phenotype allows studies on behavior and tumorigenesis of third instar larvae.  When placed on food containing 20-hydroxyecdysone (1 µg/ml), most fey homozygotes pupate though morphogenesis is arrested early.  Mixed in the substrate, any chemical can be studied for its potential of inducing pupation.

The two fey alleles were obtained from a P-element reversion experiment where the P-elements in the sra alleles sra^P1 and sra^P2 were removed.  Originally, fey¹ and fey² had been referred to as sra^l1 and sra^l2, respectively, (Czank 1998) as the result of the fact that P-element removal was a "sra allele" that was homozygous lethal and had a sra phenotype in trans-heterozygous sra/sra^l1 or sra/sra^l2 animals.  A genomic rescue with a construct containing the sra genomic DNA including the 5’ regulatory sequences was performed.  This rescue construct reverted the sra phenotype (studied in trans-heterozygotes) but not the lethality.  Therefore, we believe that the original P-element removal was imprecise and thus causing a mutant sra allele, and, as an additional effect, caused a mutation in fey.  This is possible as the P-elements in sra^P1 and sra^P2 have inserted in the large sra intron that might harbor regulatory sequences for fey.  However, we cannot exclude that our rescue construct was lacking stage specific regulatory sequences for sra.  If so, fey would be a lethal sra allele.

The two genes, fey and sra, lie in the same genomic region 89B12.  When fey¹ or fey² is crossed to flies with Df(3R)sbd²⁶, Df(3R)sbd⁴⁵ or Df(3R)sbd¹⁰⁴, no adult fey/Df(3R)sbd trans-heterozygotes are found.  These sbd deletions also uncover sra.  Two stocks are available, UM3 and UM4, the flies have the genotype cn; ry fey¹ sra³/TM6B, Tb e and w; fey² sra⁴/TM6B, Tb e, respectively.

            References:  Czank, A., 1998,  sarah, a novel gene affecting reproduction of Drosophila melonogaster females:  Phenotype analysis and cloning.  Ph.D. thesis, University of Zurich, Switzerland.