10 research outputs found
A comparative view on sex differentiation and gametogenesis genes in lungfish and coelacanths
none8siGonadal sex differentiation andreproductionare the keys totheperpetuationof favorable gene combinations andpositively selected
traits. In vertebrates, several gonad development features that differentiate tetrapods and fishes are likely to be, at least in part,
related to the water-to-land transition. The collection of information from basal sarcopterygians, coelacanths, and lungfishes, is
crucial to improve our understanding of the molecular evolution of pathways involved in reproductive functions, since these
organisms are generally regarded as âliving fossilsâ and as the direct ancestors of tetrapods. Here, we report for the first time the
characterization of >50 genes related to sex differentiation and gametogenesis in Latimeria menadoensis and Protopterus
annectens. Although the expression profiles of most genes is consistent with the intermediate position of basal sarcopterygians
between actinopterygian fish and tetrapods, their phylogenetic placement and presence/absence patterns often reveal a closer
affinity to the tetrapod orthologs. On the other hand, particular genes, for example, the male gonad factor gsdf (Gonadal
Soma-Derived Factor), provide examples of ancestral traits sharedwith actinopterygians,which disappeared in the tetrapod lineage.openMaria Assunta Biscotti, Mateus Contar Adolfi, Marco Barucca, Mariko Forconi, Alberto Pallavicini, Marco Gerdol, Adriana Canapa, Manfred SchartlBiscotti, Maria Assunta; Contar Adolfi, Mateus; Barucca, Marco; Forconi, Mariko'; Pallavicini, Alberto; Gerdol, Marco; Canapa, Adriana; Schartl, Manfre
Geschlechtsbestimmung und Meiose in Medaka: Die Rolle der RetinsÀure
Sex determination (SD) is a complex and diverse developmental process that leads to the decision whether the bipotential gonad anlage will become a testis or an ovary. This mechanism is regulated by gene cascades, networks and/or chromosomal systems, and can be influenced by fluctuations of extrinsic factors like temperature, exposure to hormones and pollution. Within vertebrates, the group of fish show the widest variety of sex determination mechanism. This whole diversity of processes and mechanisms converges to the formation of two different gametes, the eggs and the sperm, the first bigger and static, and the second smaller and motile. Meiosis is crucial for the formation of both types of gametes, and the timing of meiosis entry is one of the first recognizable differences between male and female in vertebrates. The germ cells go into meiosis first in female than in male, and in mammals, this event has been shown to be regulated by retinoic acid (RA). This small polar molecule induces in the germ cells the expression of the pre-meiotic marker Stra8 (stimulated by retinoic acid gene 8), which is necessary for meiosis initiation. Interestingly, genome analyzes have shown that the majority of fish (including medaka) lack the stra8 gene, adding a question mark to the role of RA in meiosis induction in this group. Since a role of RA in entry of meiosis and sexual development of fish is still far from being understood, I investigated in medaka (Oryzias latipes) a possible signaling function of RA during the SD period in embryos and in reproductively active gonads of adults. I generated a transgenic medaka line that reports responsiveness to RA in vivo. With this tool, I compared RA responsiveness with the expression of the main gene involved in the synthesis of RA. My results show that there is a de-correlation between the action of RA with its source. In adults, expression of the RA metabolizing enzymes show sexually dimorphic RA levels, with aldh1a2 levels being higher in testis, and cyp26a1 stronger in female gonad. In ovary, the responsiveness is restricted to the early meiotic oocytes. In testis, RA is acting directly in the pre-meiotic cells, but also in Sertoli and Leydig cells. Treatment experiments on testis organ culture showed that RA pathway activation leads to a decrease in meiosis markers expression levels. During the development, RA responsiveness in the germ cells was observed in both sexes much earlier than the first female meiosis entry. Treatments with RA-synthesis inhibitor show a decrease in meiosis markers expression levels only after the sex differentiation period in female. Expression analyzes of embryos treated with exogenous RA showed induction of dmrt1a at the gonad levels and an increase of amh levels. Both genes are not only involved in male formation, but also in the regulation of germ cell proliferation and differentiation. RA is important in meiosis induction and gametogenesis in adult medaka. However, there is no evidence for a similar role of RA in initiating the first meiosis in female germ cells at the SD stage. Moreover, contrary to common expectation, RA seems to induce sex related genes that are involved indirectly in meiosis inhibition. In this thesis, I showed for the first time that RA can be involved in both induction and inhibition of meiosis entry, depending on the sex and the developmental stage in a stra8-independent model organism.Geschlechtsbestimmung ist ein komplexer und vielfĂ€ltiger Entwicklungsprozess, der zu der Entscheidung fĂŒhrt, ob sich aus der bipotenten Gonadenanlage Hoden oder Ovarien entwickeln. Dieser Mechanismus ist durch Genkaskaden, Netzwerke und/oder chromosomale Systeme reguliert, kann aber auch durch Fluktuation Ă€uĂerer Faktoren wie beispielsweise Temperatur, durch Hormonexposition oder durch Umweltverschmutzung beeinflusst werden. Innerhalb der Wirbeltiere zeigen Fische die gröĂte Vielfalt in Bezug auf die Mechanismen der Geschlechtsbestimmung. Die unterschiedlichen Mechanismen der Geschlechtsbestimmung konvergieren in der Entstehung von der beiden unterschiedlichen Geschlechtszellen, der Eizelle und des Spermiums. Die Eizelle ist groĂ und statisch, das Spermium hingegen ist kleiner und beweglich. Die entscheidende Rolle fĂŒr die Entstehung der Geschlechtzellen spielt die Meiose. Der Zeitpunkt, an dem zum ersten Mal in der Entwicklung die Meiose einsetzt, ist der erste erkennbare Unterschied in der Gonadenentwicklung zwischen mĂ€nnlichen und weiblichen Wirbeltieren. Die Meiose der Keimzellen beginnt bei Weibchen frĂŒher als bei MĂ€nnchen. Bei SĂ€ugetieren reguliert RetinsĂ€ure (RA) diesen Prozess. Dieses kleine polare MolekĂŒl induziert die Expression des PrĂ€-Meiose-Markers Stra8 (stimulated by retinoic acid gene 8) in den Keimzellen, welcher fĂŒr den Eintritt in die Meiose essentiell ist. Interessanterweise haben Genomanalyzen gezeigt, dass das stra8 Gen in Medaka sowie in den meisten anderen Fischarten nicht vorhanden ist. Dies stellt eine vergleichbare Rolle von RA fĂŒr die Induktion der Meiose wie bei SĂ€ugetieren in diesen Fischen in Frage. Da die Rolle von RA fĂŒr den Eintritt in die Meiose sowie fĂŒr die Geschlechtsentwicklung in Fischen bisher nur unzureichend untersucht und verstanden ist, habe ich bei Medaka (Oryzias latipes) eine mögliche Funktion von RA fĂŒr die Geschlechtsdetermination in Embryonen sowie in Gonaden geschlechtsreifer Tiere untersucht. Ich habe im Rahmen dieser Arbet eine transgene Medakalinie generiert, die in vivo eine RA induzierte Genexpression durch ein GFP Reportergen anzeigt. Mit Hilfe dieser Linie wurde die transkriptionsreulierende AktivitĂ€t von RAmit der Expression der wichtigsten Gene, die in die RA Synthese involviert sind, verglichen. Meine Ergebnisse zeigen eine Diskrepanz zwischen dem Wirkungs- und Syntheseort von RA. Die RA metabolisierenden Enzyme zeigten eine geschlechtsdimorphe Expression in adulten Medakas, mit einer höheren aldh1a2 Expression im Hoden sowie einer stĂ€rkeren cyp26a1 Expression in weiblichen Gonaden. Im Ovar sind lediglich frĂŒhe meiotische Eizellen RA-sensitiv. Im Hoden wirkt RA direkt in prĂ€-meiotische Zellen, aber auch in Sertoli und Leydig Zellen. Stimulations-Experimente an Hoden Organkulturen ergaben, dass eine Aktivierung des RA Signalwegs zu einer Abnahme des Expressionslevels von Meiose-Markern fĂŒhrt. WĂ€hrend der Embryonalentwicklung konnte in den Keimzellen beider Geschlechter eine transkriptions-induziernende AktivitĂ€t von RA bereits zu einem Zeitpunkt beobachtet werden, der deutlich vor dem ersten Meiose Eintritt in Weibchen liegt. Behandlungen mit einem RA-Synthese Inhibitor zeigten lediglich nach der Geschlechtsdifferenzierung in Weibchen eine verminderte Expression der Meiose-Marker. Expressionsanalysen von Embryonen, die mit exogener RA behandelt wurden, ergaben eine Induktion von dmrt1a in den Gonaden und ein Anstieg von amh. Beide Gene sind sowohl in die mĂ€nnliche Geschlechtsentwicklung involviert, als auch in die Regulation der Keimzellproliferation und âdifferenzierung. Zusammen ergaben meine Untersuchungen, dass RA fĂŒr die Induktion der Meiose und der Gametogenese in adulten Medakas wichtig ist. Allerdings gibt es keinen Hinweis fĂŒr eine Ă€hnliche Rolle
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von RA bei der Initiierung der ersten Meiose in weiblichen Keimzellen wĂ€hrend der Geschlechtsdetermination. Im Gegensatz zur bisher beschriebenen Situation, scheint darĂŒber hinaus RA die Expression geschlechtsspezifischer Gene zu induzieren, die indirekt in die Inhibition der Meiose involviert sind. In der vorliegenden Arbeit konnte in einem stra8-unabhĂ€ngigen Modelorganismus das erste Mal gezeigt werden, dass RA â abhĂ€ngig vom Geschlecht und vom Stadium der Entwicklung - sowohl in die Induktion als auch in die Inhibition des Meiose-Eintritts involviert ist
Gonadal development and molecular cloning of Dmrt1 (doublesex and mab-3-related transcription factor-1) and Sox9 in South American teleosts.
As sequĂȘncias dos genes dmrt1 e sox9 em pirarucu (Arapaima gigas), lambari (Astyanax altiparanae) e piapara (Leporinus elongatus) foram analisadas por tĂ©cnicas de clonagem molecular. Fragmentos do gene dmrt1 foram clonados nas trĂȘs espĂ©cies citadas, e do gene sox9 em lambari e piapara. A anĂĄlise filogenĂ©tica destes genes mostrou concordĂąncia com os dados morfolĂłgicos da filogenia destas espĂ©cies. Pelo acompanhamento do desenvolvimento gonadal de lambari por microscopia de luz, foi constatada a presença de cĂ©lulas germinativas na regiĂŁo da futura gĂŽnada jĂĄ no perĂodo de 5 dias apĂłs eclosĂŁo (dae), sendo tambĂ©m observado que a formação de ovĂĄrio ocorre primeiro do que a formação de testĂculo. As expressĂ”es dos genes dmrt1 e sox9 por qRT-PCR em lambari mostraram maior especificidade para testĂculo do que para ovĂĄrio, indicando que possivelmente estes genes ainda possuem função macho-especĂfica nos adultos. Em lambari, os genes foram expressos em todos os perĂodos larvais, tendo uma diminuição no estĂĄgio de 12 dae, e aumentando sua expressĂŁo no estĂĄgio de 33 dae.The sequences of dmrt1 and sox9 genes were analyzed in pirarucu (Arapaima gigas), lambari (Astyanax altiparanae) and piapara (Leporinus elongatus) using molecular cloning techniques. Fragments of dmrt1 gene were cloned in these three species, and sox9 gene fragments have been acquired only for lambari and piapara. Phylogenetic analysis of the genes was shown to be consistent with the morphological phylogeny of these species. The analysis of the gonadal development in lambari was followed by light microscopy, where it was found the presence of germ cells in the region of the future gonad in 5 days after hatching (dah), and that the formation of ovaries occurs first comparing to the formation of testis. The gene expression of dmrt1 and sox9 by qRT-PCR method show specificity for testis comparing to ovary, which indicates that these genes also have a male-specific role in the adult. In lambari, the genes were expressed in all larval periods, with a decrease of expression levels in 12 dah, and increasing its expression at stage of 33 dah
The replaceable master of sex determination: bottom-up hypothesis revisited
International audienceDifferent group of vertebrates and invertebrates demonstrate an amazing diversity of gene regulations not only at the top but also at the bottom of the sex determination genetic network. As early as 1995, based on emerging findings in Drosophila melanogaster and Caenorhabditis elegans , Wilkins suggested that the evolution of the sex determination pathway evolved from the bottom to the top of the hierarchy. Based on our current knowledge, this review revisits the âbottom-upâ hypothesis and applies its logic to vertebrates. The basic operation of the determination network is through the dynamics of the opposing male and female pathways together with a persistent need to maintain the sexual identity of the cells of the gonad up to the reproductive stage in adults. The sex-determining trigger circumstantially acts from outside the genetic network, but the regulatory network is not built around it as a main node, thus maintaining the genetic structure of the network. New sex-promoting genes arise either through allelic diversification or gene duplication and act specially at the sex-determination period, without integration into the complete network. Due to this peripheral position the new regulator is not an indispensable component of the sex-determining network and can be easily replaced. This article is part of the theme issue âChallenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part I)â
Evolution of the Degenerated Y-Chromosome of the Swamp Guppy, Micropoecilia picta
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
The transcriptome of the newt Cynops orientalis provides new insights into evolution and function of sexual gene networks in sarcopterygians
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
Evolution of the degenerated Y-chromosome of the swamp guppy, Micropoecilia picta
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 Endlerâs 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
The sterlet sturgeon genome sequence and the mechanisms of segmental rediploidization
Sturgeons seem to be frozen in time. The archaic characteristics of this ancient fish lineage place it in a key phylogenetic position at the base of the ~30,000 modern teleost fish species. Moreover, sturgeons are notoriously polyploid, providing unique opportunities to investigate the evolution of polyploid genomes. We assembled a high-quality chromosome-level reference genome for the sterlet, Acipenser ruthenus. Our analysis revealed a very low protein evolution rate that is at least as slow as in other deep branches of the vertebrate tree, such as that of the coelacanth. We uncovered a whole-genome duplication that occurred in the Jurassic, early in the evolution of the entire sturgeon lineage. Following this polyploidization, the rediploidization of the genome included the loss of whole chromosomes in a segmental deduplication process. While known adaptive processes helped conserve a high degree of structural and functional tetraploidy over more than 180 million years, the reduction of redundancy of the polyploid genome seems to have been remarkably random.publishe