Tubby-tagged balancers for the Drosophila X and second chromosomes

Abstract

One of the great advantages of Drosophila melanogaster as model organism is the availability of balancer chromosomes. These chromosomes suppress recombination with their homologues, allowing the maintenance of lethal and sterile mutants as balanced heterozygotes. All balancers carry dominant markers that are visible in adult flies, but only a subset have markers that unambiguously distinguish homozygous mutant larvae from their heterozygous siblings. The latter balancers include those that express high levels of the GFP protein under the indirect control, via the UAS/GAL4 system, of either the Kruppel (Kr), 1 or hsp70, 2 promoter. In addition, there are direct-drive balancers that express GFP under the control of the actin A5c promoter 3 or YFP under the control of Deformed (Dfd HZ2.7rev) or glass (GMR) enhancer elements. 4 Each of the GFP-or YFP-expressing balancers has specific advantages, but all share a common drawback: These balancers require the use of a dissecting microscope equipped with an UV light source, which for reliable fluorescence detection is preferably used in the dark.The TM6B balancer 5 carries the Tb 1 dominant mutation, which results in squat larvae and pupae. We have been using this balancer for many years to unambiguously distinguish homozygous mitotic mutants dying at late larval stages from their heterozygous siblings (reviewed in ref. 6). This balancer proved particularly useful when mutant larvae are rare and one has to examine several vials (or bottles) to find third instar larvae suitable for dissection and cytological analysis. To generate new tools for easy detection of larvae homozygous for lethal mutations on the X or the second chromosome, we decided to generate males to w/w females (TMS is a Δ2-3-bearing third chromosome balancer expressing the P-element transposase described in ref. 10); from approximately 1,000 progeny we recovered two FM7 chromosomes that co-segregated with Tb (we propose to name these balancers FM7-TbA and FM7-TbB). To generate a second chromosome balancer with a P{Tb 1 } insertion we used a CyO balancer bearing the additional markers S and bw 1 (designated as CyO-Sbw in FlyBase). We crossed w/w; P{Tb 1 }/CyOSbw; TMS/+ females to w; CyO/Sco males and recovered three CyO-Sbw-P{Tb 1 } chromosomes from approximately 1,000 progeny (we propose to name these balancers CyO-TbA, CyO-TbB and CyO-TbC). To assess the utility of these FM7a and CyO Tb-bearing balancers, we compared their Tb phenotype with the Tb 1 mutant phenotype associated with TM6B. 5 To quantify the squat phenotype elicited by the balancers we measured the axial ratio 11 of larvae and pupae (AR, length/width) heterozygous for each balancer. It has been previously shown that the AR does not depend on larval and pupal size and provides a reliable measure of the Tb phenotype.9 As shown in figure 1, the ARs observed in FM7-TbA, FM7-TbB, CyO-TbA, CyO-TbB, CyOTbC and TM6B heterozygotes are fully comparable and significantly different from those of wild-type or non-Tb-bearing larvae and pupae. We thus co...

Greatwall-phosphorylated Endosulfine is both an inhibitor and a substrate of PP2A-B55 heterotrimers

“…For the genes on the third chromosome ( tws, wdb, flfl, PP1-87B, PP1α-96A ) the balancers used either were TM6B, Tb 1 Antp Hu or TM6C, Tb 1 Sb 1 . For the cka gene on the second chromosome, the balancer was CyO-TbA, while for the flw gene on the X chromosome, the balancer was FM7A-TbA (Lattao et al, 2011). The wrd KG01108 mutation is homozygous viable.…”

The Hybrid Incompatibility Genes Lhr and Hmr Are Required for Sister Chromatid Detachment During Anaphase but Not for Centromere Function

“…Larvae from this homozygous stock were used for the analysis of chromosome integrity and mitotic division. The FM7-Tb and CyO-Tb balancers, which carry the dominant larval marker Tb, are described in Lattao et al (2011).…”

Intimate functional interactions between TGS1 and the Smn complex revealed by an analysis of the Drosophila eye development

“…All flies were reared according to standard procedures at 25 °C. Lethal mutations were balanced over either TM6B, Hu, Tb or CyO-TbA, Cy, Tb [45]. All genetic markers and special chromosomes are described in detail in FlyBase (http://www.flybase.org).…”