Refine
Has Fulltext
- yes (119)
Is part of the Bibliography
- yes (119)
Year of publication
Document Type
- Journal article (119) (remove)
Language
- English (119)
Keywords
- Physiologische Chemie (42)
- Schwertkärpfling (9)
- Xiphophorus (6)
- evolution (5)
- melanoma (5)
- medaka (4)
- Onkogen (3)
- Protein-Tyrosin-Kinasen (3)
- evolutionary genetics (3)
- genome (3)
- meiosis (3)
- sex chromosomes (3)
- transcriptome (3)
- Biologie (2)
- DM-domain gene (2)
- Japankärpfling (2)
- Lebendgebärende Zahnkarpfen (2)
- Mc4r (2)
- Melanom (2)
- Y chromosome (2)
- cancer (2)
- developmental biology (2)
- fish (2)
- fish model (2)
- gametogenesis (2)
- gene expression (2)
- genome annotation (2)
- genomics (2)
- microRNA (2)
- parthenogenesis (2)
- piRNA (2)
- preexisting bias (2)
- puberty (2)
- recombination (2)
- reproductive success (2)
- sequence alignment (2)
- sex determination (2)
- sex differentiation (2)
- sexual selection (2)
- synaptonemal complex (2)
- testis (2)
- transposable elements (2)
- zebrafish (2)
- 5-methylcytosine (1)
- Acipenser baerii (1)
- Amazon Molly (1)
- Annotation (1)
- Aulonocara (1)
- BMP signaling (1)
- Biology (1)
- Buntbarsche (1)
- Cell-line (1)
- Co-option (1)
- Coahuila (1)
- CrossQuery (1)
- Cynoglossus semilaevis (1)
- DMRT1 (1)
- DNA fingerprinting (1)
- DNA-binding proteins (1)
- Danio-rerio (1)
- Dmrt1bY (1)
- Drosophila melanogaster (1)
- Egfr (1)
- Embryo (1)
- Enhancer (1)
- Epidermaler Wachstumsfaktor-Rezeptor (1)
- Eukaryoten (1)
- Fische (1)
- Fish (1)
- Freeze-etching (1)
- Förster Resonance Energy Transfer (1)
- Gen (1)
- Gene expression analysis (1)
- Genome (1)
- Genome assembly (1)
- Genome comparison (1)
- Genomics (1)
- Gentransfer (1)
- Germline (1)
- Gewebe (1)
- Goldbrasse (1)
- Human (1)
- In vitro (1)
- In vivo (1)
- Isoenzym (1)
- Jmjd6 (1)
- Karyotyp (1)
- Konservierung (1)
- Krebs <Medizin> (1)
- Latimeria menadoensis (1)
- Ligand <Biochemie> (1)
- Male intromittent organ (1)
- Malignant melanoma (1)
- Medaka - Genetransfer - Transient expression - DNA fate - Fish developmental biology (1)
- Medizin (1)
- Megalobrama amblycephala (1)
- Melanoma (1)
- Messenger-RNS (1)
- Microarray data (1)
- NGS (1)
- Nervenzelle (1)
- Niedere Wirbeltiere (1)
- Njassasee (1)
- PCR (1)
- PI3K (1)
- Pain (1)
- Perugia-Kärpfling (1)
- Poecilia (Teleostei: Poeciliidae) (1)
- Poeciliid fish (1)
- Promotor (1)
- Protoonkogen (1)
- Protopterus annectens (1)
- RAS (1)
- RNA-SEQ data (1)
- RNA-Seq (1)
- RNA-seq transcriptome (1)
- RT -PCR (1)
- RTK (1)
- Recombinant DNA ; Growth hormone gene ; PCR; Silver carp ; Fish (1)
- Recombinant DNA ; polymerase chain reaction ; metallothionein gene ; rainbow trout ; fish (1)
- SGNH hydrolase (1)
- SMAD signaling (1)
- SOX9 (1)
- Schwertkräpfling (1)
- Sex chromosome (1)
- Sex determination (1)
- Sexual development and function (1)
- Single nucleotide change (1)
- Somatotropin (1)
- Sox5 (1)
- Sparus aurata (1)
- Spongilla lacustris (1)
- Sprouting angiogenesis (1)
- Squalius alburnoides (1)
- Synaptische Vesikel (1)
- Synaptophysin (1)
- Süßwasserpolypen (1)
- Transcription (1)
- Transcriptomic (1)
- Transgene Tiere (1)
- Transmission electron microscopy (1)
- Transposable element (1)
- Tumor (1)
- Tumorzelle (1)
- Veracruz <Stadt> (1)
- Wachstum (1)
- X. couchianus (1)
- X. hellerii (1)
- Xiphophorus fish (1)
- Y chromosome degeneration (1)
- Zebrafish (1)
- achiasmatic (1)
- acipenserid minisatellite (1)
- adaptive evolution (1)
- adaptive radiation (1)
- all-fish genes (1)
- amphimixis (1)
- androgen-induced masculinization (1)
- animal physiology (1)
- apomixis (1)
- automixis (1)
- beetle horns (1)
- bioinformatics (1)
- cancer genomics (1)
- cancer models (1)
- cell fusion (1)
- cell proliferation (1)
- cellline transfection (1)
- chain reaction (1)
- chemotherapy resistance (1)
- chimera formation (1)
- chimeric RTKs (1)
- coloration (1)
- comparative genomics (1)
- contributes (1)
- copy-number alteration (1)
- crossing-over (1)
- crosstalk (1)
- cultures (1)
- determination locus (1)
- determining genes (1)
- deuterostomes (1)
- differentiation (1)
- dimorphic expression (1)
- divergent expression regulation (1)
- drug selection (1)
- embryonic stem-cells (1)
- energy homeostasis (1)
- epidermal growth factor receptor (1)
- evolutionary mutant model (1)
- exaptation (1)
- experimental evolution (1)
- expression (1)
- expression analysis (1)
- factor acetylhydrolase activity (1)
- fishes Xiphophorus (1)
- fluorescence lifetime imaging microscopy (1)
- gene (1)
- gene duplications (1)
- gene prediction (1)
- gene regulatory network evolution (1)
- generation (1)
- genetic markers (1)
- genetic oscillators (1)
- genome assembly (1)
- genome cells (1)
- genome evolution (1)
- genomic organization (1)
- genus Xiphophorus (1)
- gonadal development (1)
- gonopodium (1)
- growth (1)
- growth hormone gene (1)
- gut microflora (1)
- gynogeaesls (1)
- gynogenesis (1)
- helitron (1)
- herbivorous diet (1)
- heterochromatin (1)
- heterogamety (1)
- human genomics (1)
- hybrid origin (1)
- hybridogenesis (1)
- ichthyology (1)
- in-vitro (1)
- intermuscular bone (1)
- introgressive hybridization (1)
- key innovation (1)
- kinase inhibitors (1)
- knockout (1)
- likelihood approach (1)
- linkage map (1)
- luciferase (1)
- lungfish (1)
- male size polymorphism (1)
- male-specific traits (1)
- malignant tumors (1)
- master sex-determining gene (1)
- medaka fish (1)
- medakafish oryzias latipes (1)
- melanogenesis (1)
- metastatic melanoma (1)
- miR-146a (1)
- miR-193a (1)
- mini-exon (1)
- mitochondrial DNA (1)
- mitochondrial genome (1)
- molecular biology (1)
- molecular mechanisms (1)
- molecular phylogeny (1)
- monodelphis domestica (1)
- mouse (1)
- mouse testis differentiation (1)
- mullerian hormone AMH (1)
- natural variation (1)
- oogenesis (1)
- oreochromis niloticus (1)
- oryzias latipes (1)
- oryzias-latipes (1)
- ovary (1)
- paralogs (1)
- parten-offspring conflict (1)
- phenotypic screening (1)
- pigment pattern (1)
- platelet activation factor (1)
- platyfish (1)
- pluripotency (1)
- poeciliid fishes (1)
- poeciliidae (1)
- polymerase (1)
- polyploidy (1)
- pp6oc-src (1)
- ras (1)
- receptor tyrosine kinase (1)
- regulatory regions (1)
- reproductive character displacement (1)
- retinoic acid (1)
- retrotransposons (1)
- rolling-circle transposons (1)
- sarcopterygian fish (1)
- satellite DNA (1)
- sex chromosome evolution (1)
- sex combs (1)
- sex linked pigmentation pattern (1)
- sex-determining region (1)
- sexual antagonistic genes (1)
- sexual conflict (1)
- sexually antagonistic genes (1)
- simple repeat sequences (1)
- simple repetitive sequences (1)
- size polymorpbism (1)
- small RNA-sequencing (1)
- sodal domlnance (1)
- species diversification (1)
- spermatogenesis (1)
- squalius alburnoides (1)
- stage III (1)
- sturgeon (1)
- sturgeon karyotype (1)
- swordtails (1)
- tandem repeats (1)
- teleost fish (1)
- teleost fishes (1)
- teleost flsh (1)
- teleostei (1)
- testosterone (1)
- topminnow (1)
- transcriptional rewiring (1)
- transgenic fish (1)
- transplantation (1)
- transposition (1)
- tree selection (1)
- variant detection (1)
- vertebrates (1)
- whole genome (1)
- whole genome duplication (1)
- whole genome duplications (1)
- whole-genome duplication (1)
- whole-genome sequencing (1)
- xiphophorus maculatus (1)
Institute
- Theodor-Boveri-Institut für Biowissenschaften (119) (remove)
The remarkable diversity of sex determination mechanisms known in fish may be fuelled by exceptionally high rates of sex chromosome turnovers or transitions. However, the evolutionary causes and genomic mechanisms underlying this variation and instability are yet to be understood. Here we report on an over 30-year evolutionary experiment in which we tested the genomic consequences of hybridisation and selection between two Xiphophorus fish species with different sex chromosome systems. We find that introgression and imposing selection for pigmentation phenotypes results in the retention of an unexpectedly large maternally derived genomic region. During the hybridisation process, the sex-determining region of the X chromosome from one parental species was translocated to an autosome in the hybrids leading to the evolution of a new sex chromosome. Our results highlight the complexity of factors contributing to patterns observed in hybrid genomes, and we experimentally demonstrate that hybridisation can catalyze rapid evolution of a new sex chromosome.
We have sequenced the genome of the largest freshwater fish species of the world, the arapaima. Analysis of gene family dynamics and signatures of positive selection identified genes involved in the specific adaptations and unique features of this iconic species, in particular it’s large size and fast growth. Genome sequences from both sexes combined with RAD-tag analyses from other males and females led to the isolation of male-specific scaffolds and supports an XY sex determination system in arapaima. Whole transcriptome sequencing showed that the product of the gland-like secretory organ on the head surface of males and females may not only provide nutritional fluid for sex-unbiased parental care, but that the organ itself has a more specific function in males, which engage more in parental care.
The piranha enjoys notoriety due to its infamous predatory behavior but much is still not understood about its evolutionary origins and the underlying molecular mechanisms for its unusual feeding biology. We sequenced and assembled the red-bellied piranha (Pygocentrus nattereri) genome to aid future phenotypic and genetic investigations. The assembled draft genome is similar to other related fishes in repeat composition and gene count. Our evaluation of genes under positive selection suggests candidates for adaptations of piranhas’ feeding behavior in neural functions, behavior, and regulation of energy metabolism. In the fasted brain, we find genes differentially expressed that are involved in lipid metabolism and appetite regulation as well as genes that may control the aggression/boldness behavior of hungry piranhas. Our first analysis of the piranha genome offers new insight and resources for the study of piranha biology and for feeding motivation and starvation in other organisms.
In mammals the melanocortin 4 receptor (Mc4r) signaling system has been mainly associated with the regulation of appetite and energy homeostasis. In fish of the genus Xiphophorus (platyfish and swordtails) puberty onset is genetically determined by a single locus, which encodes the mc4r. Wild populations of Xiphophorus are polymorphic for early and late-maturing individuals. Copy number variation of different mc4r alleles is responsible for the difference in puberty onset. To answer whether this is a special adaptation of the Mc4r signaling system in the lineage of Xiphophorus or a more widely conserved mechanism in teleosts, we studied the role of Mc4r in reproductive biology of medaka (Oryzias latipes), a close relative to Xiphophorus and a well-established model to study gonadal development. To understand the potential role of Mc4r in medaka, we characterized the major features of the Mc4r signaling system (mc4r, mrap2, pomc, agrp1). In medaka, all these genes are expressed before hatching. In adults, they are mainly expressed in the brain. The transcript of the receptor accessory protein mrap2 co-localizes with mc4r in the hypothalamus in adult brains indicating a conserved function of modulating Mc4r signaling. Comparing growth and puberty between wild-type and mc4r knockout medaka revealed that absence of Mc4r does not change puberty timing but significantly delays hatching. Embryonic development of knockout animals is retarded compared to wild-types. In conclusion, the Mc4r system in medaka is involved in regulation of growth rather than puberty.
Allopolyploid plants are long known to be subject to a homoeolog expression bias of varying degree. The same phenomenon was only much later suspected to occur also in animals based on studies of single selected genes in an allopolyploid vertebrate, the Iberian fish Squalius alburnoides. Consequently, this species became a good model for understanding the evolution of gene expression regulation in polyploid vertebrates. Here, we analyzed for the first time genome-wide allele-specific expression data from diploid and triploid hybrids of S. alburnoides and compared homoeolog expression profiles of adult livers and of juveniles. Co-expression of alleles from both parental genomic types was observed for the majority of genes, but with marked homoeolog expression bias, suggesting homoeolog specific reshaping of expression level patterns in hybrids. Complete silencing of one allele was also observed irrespective of ploidy level, but not transcriptome wide as previously speculated. Instead, it was found only in a restricted number of genes, particularly ones with functions related to mitochondria and ribosomes. This leads us to hypothesize that allelic silencing may be a way to overcome intergenomic gene expression interaction conflicts, and that homoeolog expression bias may be an important mechanism in the achievement of sustainable genomic interactions, mandatory to the success of allopolyploid systems, as in S. alburnoides.
Transposable elements are endogenous DNA sequences able to integrate into and multiply within genomes. They constitute a major source of genetic innovations, as they can not only rearrange genomes but also spread ready-to-use regulatory sequences able to modify host gene expression, and even can give birth to new host genes. As their evolutionary success depends on their vertical transmission, transposable elements are intrinsically linked to reproduction. In organisms with sexual reproduction, this implies that transposable elements have to manifest their transpositional activity in germ cells or their progenitors. The control of sexual development and function can be very versatile, and several studies have demonstrated the implication of transposable elements in the evolution of sex. In this review, we report the functional and evolutionary relationships between transposable elements and sexual reproduction in animals. In particular, we highlight how transposable elements can influence expression of sexual development genes, and how, reciprocally, they are tightly controlled in gonads. We also review how transposable elements contribute to the organization, expression and evolution of sexual development genes and sex chromosomes. This underscores the intricate co-evolution between host functions and transposable elements, which regularly shift from a parasitic to a domesticated status useful to the host.
Icefishes (suborder Notothenioidei; family Channichthyidae) are the only vertebrates that lack functional haemoglobin genes and red blood cells. Here, we report a high-quality genome assembly and linkage map for the Antarctic blackfin icefish Chaenocephalus aceratus, highlighting evolved genomic features for its unique physiology. Phylogenomic analysis revealed that Antarctic fish of the teleost suborder Notothenioidei, including icefishes, diverged from the stickleback lineage about 77 million years ago and subsequently evolved cold-adapted phenotypes as the Southern Ocean cooled to sub-zero temperatures. Our results show that genes involved in protection from ice damage, including genes encoding antifreeze glycoprotein and zona pellucida proteins, are highly expanded in the icefish genome. Furthermore, genes that encode enzymes that help to control cellular redox state, including members of the sod3 and nqo1 gene families, are expanded, probably as evolutionary adaptations to the relatively high concentration of oxygen dissolved in cold Antarctic waters. In contrast, some crucial regulators of circadian homeostasis (cry and per genes) are absent from the icefish genome, suggesting compromised control of biological rhythms in the polar light environment. The availability of the icefish genome sequence will accelerate our understanding of adaptation to extreme Antarctic environments.
Cell culture and protein target-based compound screening strategies, though broadly utilized in selecting candidate compounds, often fail to eliminate candidate compounds with non-target effects and/or safety concerns until late in the drug developmental process. Phenotype screening using intact research animals is attractive because it can help identify small molecule candidate compounds that have a high probability of proceeding to clinical use. Most FDA approved, first-in-class small molecules were identified from phenotypic screening. However, phenotypic screening using rodent models is labor intensive, low-throughput, and very expensive. As a novel alternative for small molecule screening, we have been developing gene expression disease profiles, termed the Transcriptional Disease Signature (TDS), as readout of small molecule screens for therapeutic molecules. In this concept, compounds that can reverse, or otherwise affect known disease-associated gene expression patterns in whole animals may be rapidly identified for more detailed downstream direct testing of their efficacy and mode of action. To establish proof of concept for this screening strategy, we employed a transgenic strain of a small aquarium fish, medaka (Oryzias latipes), that overexpresses the malignant melanoma driver gene xmrk, a mutant egfr gene, that is driven by a pigment cell-specific mitf promoter. In this model, melanoma develops with 100% penetrance. Using the transgenic medaka malignant melanoma model, we established a screening system that employs the NanoString nCounter platform to quantify gene expression within custom sets of TDS gene targets that we had previously shown to exhibit differential transcription among xmrk-transgenic and wild-type medaka. Compound-modulated gene expression was identified using an internet-accessible custom-built data processing pipeline. The effect of a given drug on the entire TDS profile was estimated by comparing compound-modulated genes in the TDS using an activation Z-score and Kolmogorov-Smirnov statistics. TDS gene probes were designed that target common signaling pathways that include proliferation, development, toxicity, immune function, metabolism and detoxification. These pathways may be utilized to evaluate candidate compounds for potential favorable, or unfavorable, effects on melanoma-associated gene expression. Here we present the logistics of using medaka to screen compounds, as well as, the development of a user-friendly NanoString data analysis pipeline to support feasibility of this novel TDS drug-screening strategy.
MicroRNAs play a crucial role in eukaryotic gene regulation. For a long time, only little was known about microRNA-based gene regulatory mechanisms in polyploid animal genomes due to difficulties of polyploid genome assembly. However, in recent years, several polyploid genomes of fish, amphibian, and even invertebrate species have been sequenced and assembled. Here we investigated several key microRNA-associated genes in the recently sequenced sterlet (Acipenser ruthenus) genome, whose lineage has undergone a whole genome duplication around 180 MYA. We show that two paralogs of drosha, dgcr8, xpo1, and xpo5 as well as most ago genes have been retained after the acipenserid-specific whole genome duplication, while ago1 and ago3 genes have lost one paralog. While most diploid vertebrates possess only a single copy of dicer1, we strikingly found four paralogs of this gene in the sterlet genome, derived from a tandem segmental duplication that occurred prior to the last whole genome duplication. ago1,3,4 and exportins1,5 look to be prone to additional segment duplications producing up to four-five paralog copies in ray-finned fishes. We demonstrate for the first time exon microsatellite amplification in the acipenserid drosha2 gene, resulting in a highly variable protein product, which may indicate sub- or neofunctionalization. Paralogous copies of most microRNA metabolism genes exhibit different expression profiles in various tissues and remain functional despite the rediploidization process. Subfunctionalization of microRNA processing gene paralogs may be beneficial for different pathways of microRNA metabolism. Genetic variability of microRNA processing genes may represent a substrate for natural selection, and, by increasing genetic plasticity, could facilitate adaptations to changing environments.
Amphibians evolved in the Devonian period about 400 Mya and represent a transition step in tetrapod evolution. Among amphibians, high-throughput sequencing data are very limited for Caudata, due to their largest genome sizes among terrestrial vertebrates. In this paper we present the transcriptome from the fire bellied newt Cynops orientalis. Data here presented display a high level of completeness, comparable to the fully sequenced genomes available from other amphibians. Moreover, this work focused on genes involved in gametogenesis and sexual development. Surprisingly, the gsdf gene was identified for the first time in a tetrapod species, so far known only from bony fish and basal sarcopterygians. Our analysis failed to isolate fgf24 and foxl3, supporting the possible loss of both genes in the common ancestor of Rhipidistians. In Cynops, the expression analysis of genes described to be sex-related in vertebrates singled out an expected functional role for some genes, while others displayed an unforeseen behavior, confirming the high variability of the sex-related pathway in vertebrates.
Polyploid genomes present a challenge for cytogenetic and genomic studies, due to the high number of similar size chromosomes and the simultaneous presence of hardly distinguishable paralogous elements. The karyotype of the Siberian sturgeon (Acipenser baerii) contains around 250 chromosomes and is remarkable for the presence of paralogs from two rounds of whole-genome duplications (WGD). In this study, we applied the sterlet-derived acipenserid satDNA-based whole chromosome-specific probes to analyze the Siberian sturgeon karyotype. We demonstrate that the last genome duplication event in the Siberian sturgeon was accompanied by the simultaneous expansion of several repetitive DNA families. Some of the repetitive probes serve as good cytogenetic markers distinguishing paralogous chromosomes and detecting ancestral syntenic regions, which underwent fusions and fissions. The tendency of minisatellite specificity for chromosome size groups previously observed in the sterlet genome is also visible in the Siberian sturgeon. We provide an initial physical chromosome map of the Siberian sturgeon genome supported by molecular markers. The application of these data will facilitate genomic studies in other recent polyploid sturgeon species.
The unusual occurrence and developmental diversity of asexual eukaryotes remain a puzzle. De novo formation of a functioning asexual genome requires a unique assembly of sets of genes or gene states to disrupt cellular mechanisms of meiosis and gametogenesis, and to affect discrete components of sexuality and produce clonal or hemiclonal offspring. We highlight two usually overlooked but essential conditions to understand the molecular nature of clonal organisms, that is, a nonrecombinant genomic assemblage retaining modifiers of the sexual program, and a complementation between altered reproductive components. These subtle conditions are the basis for physiologically viable and genetically balanced transitions between generations. Genomic and developmental evidence from asexual animals and plants indicates the lack of complementation of molecular changes in the sexual reproductive program is likely the main cause of asexuals' rarity, and can provide an explanatory frame for the developmental diversity and lability of developmental patterns in some asexuals as well as for the discordant time to extinction estimations.
Sex determination (SD) is a highly diverse and complex mechanism. In vertebrates, one of the first morphological differences between the sexes is the timing of initiation of the first meiosis, where its initiation occurs first in female and later in male. Thus, SD is intimately related to the responsiveness of the germ cells to undergo meiosis in a sex-specific manner. In some vertebrates, it has been reported that the timing for meiosis entry would be under control of retinoic acid (RA), through activation of Stra8. In this study, we used a fish model species for sex determination and lacking the stra8 gene, the Japanese medaka (Oryzias latipes), to investigate the connection between RA and the sex determination pathway. Exogenous RA treatments act as a stress factor inhibiting germ cell differentiation probably by activation of dmrt1a and amh. Disruption of the RA degrading enzyme gene cyp26a1 induced precocious meiosis and oogenesis in embryos/hatchlings of female and even some males. Transcriptome analyzes of cyp26a1–/–adult gonads revealed upregulation of genes related to germ cell differentiation and meiosis, in both ovaries and testes. Our findings show that germ cells respond to RA in a stra8 independent model species. The responsiveness to RA is conferred by sex-related genes, restricting its action to the sex differentiation period in both sexes.
Arapaima gigas is one of the largest freshwater fish species of high ecological and economic importance. Overfishing and habitat destruction are severe threats to the remaining wild populations. By incorporating a chromosomal Hi-C contact map, we improved the arapaima genome assembly to chromosome-level, revealing an unexpected high degree of chromosome rearrangements during evolution of the bonytongues (Osteoglossiformes). Combining this new assembly with pool-sequencing of male and female genomes, we identified id2bbY, a duplicated copy of the inhibitor of DNA binding 2b (id2b) gene on the Y chromosome as candidate male sex-determining gene. A PCR-test for id2bbY was developed, demonstrating that this gene is a reliable male-specific marker for genotyping. Expression analyses showed that this gene is expressed in juvenile male gonads. Its paralog, id2ba, exhibits a male-biased expression in immature gonads. Transcriptome analyses and protein structure predictions confirm id2bbY as a prime candidate for the master sex-determiner. Acting through the TGF beta signaling pathway, id2bbY from arapaima would provide the first evidence for a link of this family of transcriptional regulators to sex determination. Our study broadens our current understanding about the evolution of sex determination genetic networks and provide a tool for improving arapaima aquaculture for commercial and conservation purposes.
Malignant melanoma incidence is rising worldwide. Its treatment in an advanced state is difficult, and the prognosis of this severe disease is still very poor. One major source of these difficulties is the high rate of metastasis and increased genomic instability leading to a high mutation rate and the development of resistance against therapeutic approaches. Here we investigate as one source of genomic instability the contribution of activation of transposable elements (TEs) within the tumor. We used the well-established medaka melanoma model and RNA-sequencing to investigate the differential expression of TEs in wildtype and transgenic fish carrying melanoma. We constructed a medaka-specific TE sequence library and identified TE sequences that were specifically upregulated in tumors. Validation by qRT- PCR confirmed a specific upregulation of a LINE and an LTR element in malignant melanomas of transgenic fish.
Unisexual reproduction, which generates clonal offspring, is an alternative strategy to sexual breeding and occurs even in vertebrates. A wide range of non-sexual reproductive modes have been described, and one of the least understood questions is how such pathways emerged and how they mechanistically proceed. The Amazon molly, Poecilia formosa, needs sperm from males of related species to trigger the parthenogenetic development of diploid eggs. However, the mechanism, of how the unreduced female gametes are produced, remains unclear. Cytological analyses revealed that the chromosomes of primary oocytes initiate pachytene but do not proceed to bivalent formation and meiotic crossovers. Comparing ovary transcriptomes of P. formosa and its sexual parental species revealed expression levels of meiosis-specific genes deviating from P. mexicana but not from P. latipinna. Furthermore, several meiosis genes show biased expression towards one of the two alleles from the parental genomes. We infer from our data that in the Amazon molly diploid oocytes are generated by apomixis due to a failure in the synapsis of homologous chromosomes. The fact that this failure is not reflected in the differential expression of known meiosis genes suggests the underlying molecular mechanism may be dysregulation on the protein level or misexpression of a so far unknown meiosis gene, and/or hybrid dysgenesis because of compromised interaction of proteins from diverged genomes.
The conspicuous colour sexual dimorphism of guppies has made them paradigmatic study objects for sex-linked traits and sex chromosome evolution. Both the X- and Y-chromosomes of the common guppy (Poecilia reticulata) are genetically active and homomorphic, with a large homologous part and a small sex specific region. This feature is considered to emulate the initial stage of sex chromosome evolution. A similar situation has been documented in the related Endler’s and Oropuche guppies (P. wingei, P. obscura) indicating a common origin of the Y in this group. A recent molecular study in the swamp guppy (Micropoecilia. picta) reported a low SNP density on the Y, indicating Y-chromosome deterioration. We performed a series of cytological studies on M. picta to show that the Y-chromosome is quite small compared to the X and has accumulated a high content of heterochromatin. Furthermore, the Y-chromosome stands out in displaying CpG clusters around the centromeric region. These cytological findings evidently illustrate that the Y-chromosome in M. picta is indeed highly degenerated. Immunostaining for SYCP3 and MLH1 in pachytene meiocytes revealed that a substantial part of the Y remains associated with the X. A specific MLH1 hotspot site was persistently marked at the distal end of the associated XY structure. These results unveil a landmark of a recombining pseudoautosomal region on the otherwise strongly degenerated Y chromosome of M. picta. Hormone treatments of females revealed that, unexpectedly, no sexually antagonistic color gene is Y-linked in M. picta. All these differences to the Poecilia group of guppies indicate that the trajectories associated with the evolution of sex chromosomes are not in parallel.
Xiphophorus fish exhibit a clear phenotypic polymorphism in puberty onset and reproductive strategies of males. In X. nigrensis and X. multilineatus, puberty onset is genetically determined and linked to a melanocortin 4 receptor (Mc4r) polymorphism of wild-type and mutant alleles on the sex chromosomes. We hypothesized that Mc4r mutant alleles act on wild-type alleles by a dominant negative effect through receptor dimerization, leading to differential intracellular signaling and effector gene activation. Depending on signaling strength, the onset of puberty either occurs early or is delayed. Here, we show by Förster Resonance Energy Transfer (FRET) that wild-type Xiphophorus Mc4r monomers can form homodimers, but also heterodimers with mutant receptors resulting in compromised signaling which explains the reduced Mc4r signaling in large males. Thus, hetero- vs. homo- dimerization seems to be the key molecular mechanism for the polymorphism in puberty onset and body size in male fish.