Genes Genet. Syst. (2012) 87, p. 99–106 Genetic dissection of Nucleoporin 160 (Nup160), a gene involved in multiple phenotypes of reproductive isolation in Drosophila Kazunori Maehara1, Takayuki Murata1, Naoki Aoyama2, Kenji Matsuno2,3 and Kyoichi Sawamura4* 1Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan 2Department of Biological Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan 3Research Institute for Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan 4Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan (Received 11 December 2011, accepted 14 February 2012) Previous reports have suggested that the Nucleoporin 160 (Nup160) gene of Drosophila simulans (Nup160sim) causes the hybrid inviability, female sterility, and morphological anomalies that are observed in crosses with D. melanogaster. Here we have confirmed this observation by transposon excision from the P{EP}Nup160EP372 insertion mutation of D. melanogaster. Null mutations of the Nup160 gene resulted in the three phenotypes caused by Nup160sim, but rever- tants of the gene did not. Interestingly, several mutations produced by excision partially complemented hybrid inviability, female sterility, or morphological anomalies. In the future, these mutations will be useful to further our under- standing of the developmental mechanisms of reproductive isolation. Based on our analyses with the Nup160sim introgression line, the lethal phase of hybrid invi- ability was determined to be during the early pupal stage. Our analysis also sug- gested that homozygous Nup160sim in D. melanogaster leads to slow development. Thus, Nup160sim is involved in multiple aspects of reproductive isolation between these two species. Key words: Drosophila, hybrid inviability, hybrid sterility, reproductive isola- tion, speciation onic development. Sturtevant (1920) intercrossed the INTRODUCTION species using chromosome anomalies and was able to A century ago, Quackenbush (1910) claimed to have deduce the genetic causes of hybrid inviability, but “the observed unisexual broods in Drosophila melanogaster. complete sterility of surviving F1 hybrids frustrated It turned out later that his D. melanogaster flies actually Sturtevant and his vision of comprehensively exploring included two species, D. melanogaster and D. simulans the genetics of interspecific differences” (Barbash, 2010). (Sturtevant, 1919). The beauty of the latter new species Genetic tricks and the serendipitous discovery of rescue was that it could be crossed with D. melanogaster, the mutations were needed before further studies could shed most-studied and best-understood species of that genus light on his questions (Provine, 1991; Sawamura, 2000; (Provine, 1991). In crosses between D. melanogaster Barbash, 2010). females and D. simulans males, only sterile female Thanks to recent advances in molecular biology tech- hybrids are obtained, as male hybrids die during larval niques and genomic sequencing (Adams et al., 2000; Dros- development. In the reciprocal cross, sterile male ophila 12 Genomes Consortium, 2007), detailed study of hybrids appear, as most female hybrids die during embry- speciation has become feasible. As a result, several genes for hybrid inviability and sterility have recently Edited by Etsuko Matsuura been isolated in this pair of species and characterized at * Corresponding author. E-mail: [email protected] the molecular level (reviewed in Sawamura, 2012). The 100 K. MAEHARA et al. D. melanogaster gene Hybrid male rescue (Hmr) encodes (Nup160) causes inviability and female sterility when a DNA-binding protein that is involved in hybrid inviabil- introgressed into D. melanogaster; the hybrid males with ity and female sterility (Hutter and Ashburner, 1987; the introgression (or deficiency) cannot be rescued by Lhr Barbash and Ashburner, 2003; Barbash et al., 2003). D. and introgression homozygous (or hemizygous) females simulans Lethal hybrid rescue (Lhr) encodes a heterochro- are sterile (Tang and Presgraves, 2009; Sawamura et al., matin protein that causes hybrid inviability (Watanabe, 2010). 1979; Brideau et al., 2006; Prigent et al., 2009). D. mel- Nup160 , like the other genes, has been mapped by anogaster zygotic hybrid rescue (zhr) consists of hetero- recombination and deficiencies, identified by complemen- chromatic 359-bp repetitive sequences and causes hybrid tation tests against mutations, and confirmed by gene inviability in crosses involving D. simulans females transformation (Sawamura, 2000; Presgraves, 2003; (Sawamura et al., 1993; Ferree and Barbash, 2009). Sawamura et al., 2004, 2010; Tang and Presgraves, 2009). JYalpha, a gene located on different chromosomes in D. Three recessive lethal insertion mutations of Nup160 melanogaster and D. simulans, causes male sterility of have been reported in D. melanogaster (Fig. 1A; Tweedie introgression homozygotes (Muller and Pontecorvo, 1940; et al., 2009; http://flybase.org/). PBac{RB}RfC38e00704 Masly et al., 2006). D. simulans Nucleoporin 96 (Nup96) uncovers both hybrid inviability and female sterility when causes inviability when it is hemizygous in the hybrid; heterozygous with the wild-type allele of D. simulans, the hybrid males cannot be rescued by the Lhr mutation Nup160sim (Tang and Presgraves, 2009; Sawamura et al., (Presgraves et al., 2003). D. simulans Nucleoporin 160 2010). P{EP}Nup160EP372, which is synonymous with Fig. 1. Transposon insertions in the Nup160 gene and mating schemes to examine the effects of Nup160EP372 derivatives. A, Posi- tions and directions of three transposon insertions (triangles and arrows, not to scale). Open reading frames (full or partial) of Csl4, Nup160, and RfC38 are indicated (exons are numbered). UTR, untranslated region. B, Cross used to test the effects of mutations on morphology and female fertility. Open chromosome regions are from D. melanogaster; shaded regions are from D. simulans. C, Cross used to test the effects of mutations on hybrid viability. Int, Int(2L)D+S, Nup160sim; *, Nup160EP372 derivative. Reproductive isolation in Drosophila 101 P{EP}CG4738EP372, does not lead to hybrid inviability or neighboring gene RfC38, they were made heterozygous female sterility (Tang and Presgraves, 2009; Sawamura with Nup160EP372, Nup160e00704, and RfC38k13807. At the et al., 2010). Interestingly, P{lacW}l(2)SH2055SH2055 opposite end of Nup160, the region containing Csl4s has does not lead to hybrid inviability but does partially lead not been examined genetically, because no appropriate to hybrid female sterility (Sawamura et al., 2010). These mutations or deletions are known. Flies heterozygous for three mutations raise questions about why they behave Nup160sim and each derivative were produced by crossing differently and about the possibility of distinct mecha- introgression carrier females (Int(2L)D+S, Nup160sim/CyO) nisms underlying hybrid inviability and female sterility. to male derivative heterozygotes (Fig. 1B), and morphologi- In the present study, we excised the P transposable ele- cal anomalies (abdomen, wing, and bristle defects) and ment from the P{EP}Nup160EP372 insertion and examined female fertility were examined as described (Sawamura et whether the new mutations cause hybrid inviability and al., 2010). To test hybrid inviability, derivative carrier female sterility. Because Nup160 has been implicated as females were crossed to D. simulans Lhr males (Fig. 1C). the cause of morphological anomalies by deficiency map- All experiments were conducted at 25°C. ping (Sawamura et al., 2010), we also examined the abdo- men, wings, and bristles of flies heterozygous for Molecular characterization of mutations In the Nup160sim and excision derivatives. Finally, we deter- original homozygous lethal Nup160EP372 chromosome, an mined the lethal phase of hybrid males and measured the 8-kb P{EP} element is inserted in the reverse orientation total duration of development of homozygous carriers. into the 5’UTR of the Nup160 gene, which is also in the forward orientation adjacent to the 5’UTR of the Csl4 gene, at the site designated 2L: 11,123,814–11,123,822 MATERIALS AND METHODS (Berkeley Drosophila Genome Project coordinates, http:// Strain nomenclature Although PBac{RB}RfC38e00704/ genome.ucsc.edu/). GCCGGTGCC is the target site Df(2L)BSC242 and P{lacW}RfC38k13807/Df(2L)BSC242 duplication of the P element. are lethal because of the absence of Nup160 and RfC38 on DNA was extracted from derivative homozygotes (if via- Df(2L)BSC242 (Tweedie et al., 2009; http://flybase.org/), ble) or heterozygotes with CyO, and DNA fragments PBac{RB}RfC38e00704/P{lacW}RfC38k13807 flies are viable (our around the Nup160EP372 insertion site were amplified with unpublished observations). Thus, PBac{RB}RfC38e00704 the polymerase chain reaction (PCR). PCR primers and seems to carry a Nup160 mutation but not a loss-of-func- conditions are available upon request. When PCR prod- tion RfC38 mutation. In this report, therefore, we refer ucts were separated on an agarose gel, a single band (in to this insertion mutation as Nup160e00704. We also omit homozygotes) or double bands (in heterozygotes, one from the transposon symbols by designating insertion mutants the mutation allele and the other from the wild-type as Nup160EP372, Nup160SH2055, and RfC38k13807. Newly Nup160 allele on CyO) were expected. In four