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Comparative genomics has enabled the identification of genes that potentially evolved de novo from non-coding sequences. Many such genes are expressed in male reproductive tissues, but their functions remain poorly understood. To address this, we conducted a functional genetic screen of over 40 putative de novo genes with testis-enriched expression in Drosophila melanogaster and identified one gene, atlas, required for male fertility. Detailed genetic and cytological analyses showed that atlas is required for proper chromatin condensation during the final stages of spermatogenesis. Atlas protein is expressed in spermatid nuclei and facilitates the transition from histone- to protamine-based chromatin packaging. Complementary evolutionary analyses revealed the complex evolutionary history of atlas. The protein-coding portion of the gene likely arose at the base of the Drosophila genus on the X chromosome but was unlikely to be essential, as it was then lost in several independent lineages. Within the last ~15 million years, however, the gene moved to an autosome, where it fused with a conserved non-coding RNA and evolved a non-redundant role in male fertility. Altogether, this study provides insight into the integration of novel genes into biological processes, the links between genomic innovation and functional evolution, and the genetic control of a fundamental developmental process, gametogenesis., Author summary Genomes are in flux, as genes are constantly added and lost throughout evolution. New genes were once thought to arise almost exclusively via the modification or duplication of existing genes. Recently, however, interest has grown in alternative modes of new gene origination, such as de novo evolution from genetic material that previously did not encode proteins. Many de novo genes are expressed in male reproductive tissues, but their significance for fertility is not well understood. We screened likely de novo genes expressed in the Drosophila testis for reproductive roles and found one gene, atlas, essential for male fertility. We leveraged genetic and cell biological experiments to investigate roles for Atlas protein in reproduction and found that it is required during sperm development for proper packaging of DNA in the sperm nucleus. Evolutionary analyses of this gene revealed a complicated history, including loss in some lineages, movement between chromosomes, and fusion with a non-protein-coding gene. Studying both the functions and evolutionary histories of new proteins illustrates how they might evolve critical roles in biological processes despite their relative novelty. Furthermore, the study of atlas identifies an essential genetic player in the fly testis, an important model system for understanding how gametes are produced.

Comparative genomics has enabled the identification of genes that potentially evolved de novo from non-coding sequences. Many such genes are expressed in male reproductive tissues, but their functions remain poorly understood. To address this, we conducted a functional genetic screen of over 40 putative de novo genes with testis-enriched expression in Drosophila melanogaster and identified one gene, atlas, required for male fertility. Detailed genetic and cytological analyses showed that atlas is required for proper chromatin condensation during the final stages of spermatogenesis. Atlas protein is expressed in spermatid nuclei and facilitates the transition from histone- to protamine-based chromatin packaging. Complementary evolutionary analyses revealed the complex evolutionary history of atlas. The protein-coding portion of the gene likely arose at the base of the Drosophila genus on the X chromosome but was unlikely to be essential, as it was then lost in several independent lineages. Within the last ∼15 million years, however, the gene moved to an autosome, where it fused with a conserved non-coding RNA and evolved a non-redundant role in male fertility. Altogether, this study provides insight into the integration of novel genes into biological processes, the links between genomic innovation and functional evolution, and the genetic control of a fundamental developmental process, gametogenesis.Author SummaryGenomes are in flux, as genes are constantly added and lost throughout evolution. New genes were once thought to arise almost exclusively via the modification or duplication of existing genes. Recently, however, interest has grown in alternative modes of new gene origination, such as de novo evolution from genetic material that previously did not encode proteins. Many de novo genes are expressed in male reproductive tissues, but their significance for fertility is not well understood. We screened likely de novo genes expressed in the Drosophila testis for reproductive roles and found one gene, atlas, essential for male fertility. We leveraged genetic and cell biological experiments to investigate roles for Atlas protein in reproduction and found that it is required during sperm development for proper packaging of DNA in the sperm nucleus. Evolutionary analyses of this gene revealed a complicated history, including loss in some lineages, movement between chromosomes, and fusion with a non-protein-coding gene. Studying both the functions and evolutionary histories of new proteins illustrates how they might evolve critical roles in biological processes despite their relative novelty. Furthermore, the study of atlas identifies an essential genetic player in the fly testis, an important model system for understanding how gametes are produced.

Comparative genomic studies have repeatedly shown that new protein-coding genes can emerge de novo from non-coding DNA. Still unknown is how and when the structures of encoded de novo proteins emerge and evolve. Combining biochemical, genetic and evolutionary analyses, we elucidate the function and structure of goddard, a gene which appears to have evolved de novo at least 50 million years ago within the Drosophila genus.Previous studies found that goddard is required for male fertility. Here, we show that Goddard protein localizes to elongating sperm axonemes and that in its absence, elongated spermatids fail to undergo individualization. Combining modelling, NMR and CD data, we show that Goddard protein contains a large central α-helix, but is otherwise partially disordered. We find similar results for Goddard’s orthologs from divergent fly species and their reconstructed ancestral sequences. Accordingly, Goddard’s structure appears to have been maintained with only minor changes over millions of years.

Vps54 is a subunit of the Golgi-associated retrograde protein (GARP) complex, which is involved in tethering endosome-derived vesicles to the trans-Golgi network (TGN). In the wobbler mouse, a model for human motor neuron (MN) disease, reduction in the levels of Vps54 causes neurodegeneration. However, it is unclear how disruption of the GARP complex leads to MN dysfunction. To better understand the role of Vps54 in MNs, we have disrupted expression of the Vps54 ortholog in Drosophila and examined the impact on the larval neuromuscular junction (NMJ). Surprisingly, we show that both null mutants and MN-specific knockdown of Vps54 leads to NMJ overgrowth. Reduction of Vps54 partially disrupts localization of the t-SNARE, Syntaxin-16, to the TGN but has no visible impact on endosomal pools. MN-specific knockdown of Vps54 in MNs combined with overexpression of the small GTPases Rab5, Rab7, or Rab11 suppresses the Vps54 NMJ phenotype. Conversely, knockdown of Vps54 combined with overexpression of dominant negative Rab7 causes NMJ and behavioral abnormalities including a decrease in postsynaptic Dlg and GluRIIB levels without any effect on GluRIIA. Taken together, these data suggest that Vps54 controls larval MN axon development and postsynaptic density composition through a mechanism that requires Rab7., Summary: The retrograde vesicle tethering factor, Vps54, regulates development of the Drosophila larval NMJ. Moreover, presynaptic Vps54 interacts genetically with the small GTPase, Rab7, to control NMJ growth and postsynaptic density composition.

Vps54 is a subunit of the Golgi-associated retrograde protein (GARP) complex, which is involved in tethering endosome-derived vesicles to thetrans-Golgi network (TGN). In the wobbler mouse, a model for human motor neuron (MN) disease, reduction in the levels of Vps54 causes neurodegeneration. However, it is unclear how disruption of GARP-mediated vesicle transport leads to MN dysfunction and ultimately neurodegeneration. To better understand the role of Vps54 in MNs, we have disrupted expression of theVps54ortholog inDrosophilaand examined the impact on the larval neuromuscular junction (NMJ). Here, we show that both null mutants and MN-specific knockdown ofVps54leads to NMJ overgrowth. Reduction ofVps54partially disrupts localization of the t-SNARE, Syntaxin-16, to the TGN but has no impact on endosomal pools. Presynaptic knockdown ofVps54in MNs combined with overexpression of the small GTPases Rab5, Rab7, or Rab11 suppresses theVps54NMJ phenotype. Conversely, knockdown ofVps54combined with overexpression of dominant negative Rab7 causes axonal and behavioral abnormalities including a decrease in postysynaptic Dlg and GluRIIB levels without any effect on GluRIIA. Taken together, these data suggest thatVps54controls larval MN axon development and postsynaptic density composition by modulating Rab7-mediated endosomal trafficking.

Comparative genomic studies have repeatedly shown that new protein-coding genes can emerge de novo from noncoding DNA. Still unknown is how and when the structures of encoded de novo proteins emerge and evolve. Combining biochemical, genetic and evolutionary analyses, we elucidate the function and structure of goddard, a gene which appears to have evolved de novo at least 50 million years ago within the Drosophila genus. Previous studies found that goddard is required for male fertility. Here, we show that Goddard protein localizes to elongating sperm axonemes and that in its absence, elongated spermatids fail to undergo individualization. Combining modelling, NMR and circular dichroism (CD) data, we show that Goddard protein contains a large central α-helix, but is otherwise partially disordered. We find similar results for Goddard’s orthologs from divergent fly species and their reconstructed ancestral sequences. Accordingly, Goddard’s structure appears to have been maintained with only minor changes over millions of years., Previous work identified goddard as a putative de novo evolved gene in Drosophila melanogaster. Here, the authors characterize the structure and function of the Goddard protein in D. melanogaster, and they infer its ancestral and extant structures across the Drosophila genus.

Unlike many genes that arise from duplication, de novo evolved genes arise from previously noncoding DNA. Many de novo genes are expressed in the male reproductive tract, but their functions remain uncharacterized. We used an RNAi screen to identify several testis-expressed, putative de novo genes that are essential for male reproduction. Both the RNAi knockdown and the CRISPR-mediated knockout (KO) of one such gene, atlas, resulted in almost complete male sterility. Cytological analyses of spermatogenesis in atlas null mutants revealed two defects. First, mutant male testes showed few sperm in the seminal vesicle (SV) and a distended basal end of the testis, suggesting that sperm in atlas mutants are not transferred to the SV during spermatogenesis and, thus, to females during mating. Second, phalloidin staining of whole testes revealed that atlas KO males inefficiently initiate the process of spermatid individualization. To understand the normal role of atlas in spermatogenesis, we used CRISPR to scarlessly insert GFP at the end of the gene’s protein-coding sequence, at the endogenous locus. This atlas-GFP allele fully rescued the fertility defect of atlas null males. We then observed a nuclear-localized GFP signal in the post-meiotic stages of the testes. This signal overlapped partially with fully condensed sperm nuclear bundles marked by protamine-dsRed, but the GFP-positive bundles were not as close as the dsRed-positive bundles to the basal end. These data, along with the biochemical properties of the atlas protein, suggest that atlas may encode a transition protein that facilitates the replacement of histones with protamines in late spermiogenesis. These results demonstrate how a putatively de novo evolved protein can acquire an essential reproductive function.

Hypusination is a unique posttranslational modification by which lysine is transformed into the atypical amino acid hypusine. eIF5A (eukaryotic initiation factor 5A) is the only known protein to contain hypusine. In this study, we describe the identification and characterization of nero, the Drosophila melanogaster deoxyhypusine hydroxylase (DOHH) homologue. nero mutations affect cell and organ size, bromodeoxyuridine incorporation, and autophagy. Knockdown of the hypusination target eIF5A via RNA interference causes phenotypes similar to nero mutations. However, loss of nero appears to cause milder phenotypes than loss of eIF5A. This is partially explained through a potential compensatory mechanism by which nero mutant cells up-regulate eIF5A levels. The failure of eIF5A up-regulation to rescue nero mutant phenotypes suggests that hypusination is required for eIF5A function. Furthermore, expression of enzymatically impaired forms of DOHH fails to rescue nero clones, indicating that hypusination activity is important for nero function. Our data also indicate that nero and eIF5A are required for cell growth and affect autophagy and protein synthesis.

Background: The identification of the function of all genes that contribute to specific biological processes and complex traits is one of the major challenges in the postgenomic era. One approach is to employ forward genetic screens in genetically tractable model organisms. In Drosophila melanogaster, P element-mediated insertional mutagenesis is a versatile tool for the dissection of molecular pathways, and there is an ongoing effort to tag every gene with a P element insertion. However, the vast majority of P element insertion lines are viable and fertile as homozygotes and do not exhibit obvious phenotypic defects, perhaps because of the tendency for P elements to insert 5′ of transcription units. Quantitative genetic analysis of subtle effects of P element mutations that have been induced in an isogenic background may be a highly efficient method for functional genome annotation.Results: Here, we have tested the efficacy of this strategy by assessing the extent to which screening for quantitative effects of P elements on sensory bristle number can identify genes affecting neural development. We find that such quantitative screens uncover an unusually large number of genes that are known to function in neural development, as well as genes with yet uncharacterized effects on neural development, and novel loci.Conclusions: Our findings establish the use of quantitative trait analysis for functional genome annotation through forward genetics. Similar analyses of quantitative effects of P element insertions will facilitate our understanding of the genes affecting many other complex traits in Drosophila.