Birth, death, and replacement of karyopherins in Drosophila

Genetics, 2000

The KetelD dominant female-sterile mutations and their ketelr revertant alleles identify the Ketel gene, which encodes the importin-β (karyopherin-β) homologue of Drosophila melanogaster. Embryogenesis does not commence in the KetelD eggs deposited by the KetelD/+ females due to failure of cleavage nuclei formation. When injected into wild-type cleavage embryos, cytoplasm of the KetelD eggs does not inhibit nuclear protein import but prevents cleavage nuclei formation following mitosis. The Ketel+ transgenes slightly reduce effects of the KetelD mutations. The paternally derived KetelD alleles act as recessive zygotic lethal mutations: the KetelD/- hemizygotes, like the ketelr/ketelr and the ketelr/- zygotes, perish during second larval instar. The Ketel maternal dowry supports their short life. The KetelD-related defects originate most likely following association of the KetelD-encoded mutant molecules with a maternally provided partner. As in the KetelD eggs, embryogenesis does no...

Proceedings of the National Academy of Sciences of the United States of America, 1997

The ␣-and ␤-karyopherins (Kaps), also called importins, mediate the nuclear transport of proteins. All ␣-Kaps contain a central domain composed of eight approximately 40 amino acid, tandemly arranged, armadillolike (Arm) repeats. The number and order of these repeats have not changed since the common origin of fungi, plants, and mammals. Phylogenetic analysis suggests that the various ␣-Kaps fall into two groups, ␣1 and ␣2. Whereas animals encode both types, the yeast genome encodes only an ␣1-Kap. The ␤-Kaps are characterized by 14-15 tandemly arranged HEAT motifs. We show that the Arm repeats of ␣-Kaps and the HEAT motifs of ␤-Kaps are similar, suggesting that the ␣-Kaps and ␤-Kaps (and for that matter, all Arm and HEAT repeat-containing proteins) are members of the same protein superfamily. Phylogenetic analysis indicates that there are at least three major groups of ␤-Kaps, consistent with their proposed cargo specificities. We present a model in which an ␣-independent ␤-Kap progenitor gave rise to the ␣-dependent ␤-Kaps and the ␣-Kaps.

Molecular and cellular biology, 1998

Human transportin1 (hTRN1) is the nuclear import receptor for a group of pre-mRNA/mRNA-binding proteins (heterogeneous nuclear ribonucleoproteins [hnRNP]) represented by hnRNP A1, which shuttle continuously between the nucleus and the cytoplasm. hTRN1 interacts with the M9 region of hnRNP A1, a 38-amino-acid domain rich in Gly, Ser, and Asn, and mediates the nuclear import of M9-bearing proteins in vitro. Saccharomyces cerevisiae transportin (yTRN; also known as YBR017c or Kap104p) has been identified and cloned. To understanding the nuclear import mediated by yTRN, we searched with a yeast two-hybrid system for proteins that interact with it. In an exhaustive screen of the S. cerevisiae genome, the most frequently selected open reading frame was the nuclear mRNA-binding protein, Nab2p. We delineated a ca.-50-amino-acid region in Nab2p, termed NAB35, which specifically binds yTRN and is similar to the M9 motif. NAB35 also interacts with hTRN1 and functions as a nuclear localization ...

2000

D dominant female-sterile mutations and their ketel r revertant alleles identify the Ketel gene, which encodes the importin-b (karyopherin-b) homologue of Drosophila melanogaster. Embryogenesis does not commence in the Ketel D

2019

The Drosophila melanogaster Ketel gene was identified via the Ketel D dominant female sterile mutations and their ketel r revertant alleles that are recessive zygotic lethals. The maternally acting Ketel D mutations inhibit cleavage nuclei formation. We cloned the Ketel gene on the basis of a common breakpoint in 38E1.2-3 in four ketel r alleles. The Ketel ϩ transgenes rescue ketel r -associated zygotic lethality and slightly reduce Ketel D -associated dominant female sterility. Ketel is a single copy gene. It is transcribed to a single 3.6-kb mRNA, predicted to encode the 97-kD Ketel protein. The 884-amino-acid sequence of Ketel is 60% identical and 78% similar to that of human importin-␤, the nuclear import receptor for proteins with a classical NLS. Indeed, Ketel supports import of appropriately designed substrates into nuclei of digitoninpermeabilized HeLa cells. As shown by a polyclonal anti-Ketel antibody, nurse cells synthesize and transfer Ketel protein into the oocyte cytoplasm from stage 11 of oogenesis. In cleavage embryos the Ketel protein is cytoplasmic. The Ketel gene appears to be ubiquitously expressed in embryonic cells. Western blot analysis revealed that the Ketel gene is not expressed in several larval cell types of late third instar larvae.

Genetics, 2000

The Drosophila melanogaster Ketel gene was identified via the Ketel(D) dominant female sterile mutations and their ketel(r) revertant alleles that are recessive zygotic lethals. The maternally acting Ketel(D) mutations inhibit cleavage nuclei formation. We cloned the Ketel gene on the basis of a common breakpoint in 38E1. 2-3 in four ketel(r) alleles. The Ketel(+) transgenes rescue ketel(r)-associated zygotic lethality and slightly reduce Ketel(D)-associated dominant female sterility. Ketel is a single copy gene. It is transcribed to a single 3.6-kb mRNA, predicted to encode the 97-kD Ketel protein. The 884-amino-acid sequence of Ketel is 60% identical and 78% similar to that of human importin-beta, the nuclear import receptor for proteins with a classical NLS. Indeed, Ketel supports import of appropriately designed substrates into nuclei of digitonin-permeabilized HeLa cells. As shown by a polyclonal anti-Ketel antibody, nurse cells synthesize and transfer Ketel protein into the oo...

Mechanisms of Development, 2008

Developmental Biology, 2000

The Drosophila importin-␣3 gene was isolated through its interaction with the large subunit of the DNA polymerase ␣ in a two-hybrid screen. The predicted protein sequence of Importin-␣3 is 65-66% identical to those of the human and mouse importin-␣3 and ␣4 and 42.7% identical to that of Importin-␣2 (Oho31/Pendulin), the previously reported Drosophila homologue. Both Importin-␣3 and Importin-␣2 interact with similar subsets of proteins in vitro, one of which is Ketel, the importin-␤ homologue of Drosophila. importin-␣3 is an essential gene, whose encoded protein is expressed throughout development. During early embryogenesis, Importin-␣3 accumulates at the nuclear membrane of cleavage nuclei, whereas after blastoderm formation it is characteristically found within the interphase nuclei. Nuclear localisation is seen in several tissues throughout subsequent development. During oogenesis its concentration within the nurse cell nuclei increases during stages 7-10, concomitant with a decline in levels in the oocyte nucleus. Mutation of importin-␣3 results in lethality throughout pupal development. Surviving females are sterile and show arrest of oogenesis at stages 7-10. Thus, Importin-␣3-mediated nuclear transport is essential for completion of oogenesis and becomes limiting during pupal development. Since they have different expression patterns and subcellular localisation profiles, we suggest that the two importin-␣ homologues are not redundant in the context of normal Drosophila development.

Genome Biology and Evolution, 2013

Developmental conservation among related species is a common generalization known as von Baer's third law and implies that early stages of development are the most refractory to change. The "hourglass model" is an alternative view that proposes that middle stages are the most constrained during development. To investigate this issue, we undertook a genomic approach and provide insights into how natural selection operates on genes expressed during the first 24 h of Drosophila ontogeny in the six species of the melanogaster group for which whole genome sequences are available. Having studied the rate of evolution of more than 2,000 developmental genes, our results showed differential selective pressures at different moments of embryogenesis. In many Drosophila species, early zygotic genes evolved slower than maternal genes indicating that mid-embryogenesis is the stage most refractory to evolutionary change. Interestingly, positively selected genes were found in all embryonic stages even during the period with the highest developmental constraint, emphasizing that positive selection and negative selection are not mutually exclusive as it is often mistakenly considered. Among the fastest evolving genes, we identified a network of nucleoporins (Nups) as part of the maternal transcriptome. Specifically, the acceleration of Nups was driven by positive selection only in the more recently diverged species. Because many Nups are involved in hybrid incompatibilities between species of the Drosophila melanogaster subgroup, our results link rapid evolution of early developmental genes with reproductive isolation. In summary, our study revealed that even within functional groups of genes evolving under strong negative selection many positively selected genes could be recognized. Understanding these exceptions to the broad evolutionary conservation of early expressed developmental genes can shed light into relevant processes driving the evolution of species divergence.