Biology subjects

Sember, A.

Publications and source records attributed to Sember, A..

4 recordsLinked to original sources

bioRxiv2023

Formation of hemiclonal reproduction and hybridogenesis in Pelophylax water frogs studied with species-specific cytogenomic probes

Meiosis is a conservative process in all sexual organisms which ensures fertility and is central for producing genetic diversity by recombination and random segregation of parental chromosomes. Yet unexplored mechanisms may disrupt it and cause loss of sex followed by the emergence of clonal modes of reproduction. Interspecific hybridization is the primary trigger for this process, but mechanistic basis of the transition to asexuality remains still unknown for most vertebrate animals. To study these processes in water frogs, we performed reciprocal mating between two sexual species, Pelophylax ridibundus and P. lessonae, and produced vital F1 progeny (P. esculentus). The RepeatExplorer2 analysis of low-coverage genomic data of the two parental species identified the P. lessonae-specific minisatellite marker PlesSat01-48 (44 bp), which hybridized to (peri)centromeric regions of two chromosome pairs in P. lessonae - the acrocentric chromosome 8 and the chromosome 10 (a carrier of nucleolar organizer region; NOR). Chromosomal mapping combining the novel hybridization probe with the previously designed marker for P. ridibundus-specific centromeric satellite DNA showed that the P. esculentus progeny do not reproduce sexually. Instead, the F1 generation of P. esculentus instantly modified its gametogenesis and established asexual reproduction via hybridogenesis. Gametogenic modifications included premeiotic elimination of one of the parental genomes and clonal propagation of the remaining genome via endoreplication followed by standard meiotic division. The origin of DNA elimination and hybridogenesis in laboratory-produced hybrids supports a hypothesis that P. esculentus arises recurrently in nature whenever parental species come into reproductive contact. Based on the observed pattern of DNA elimination in the F1 progeny we discuss the origin and evolution of population systems in water frogs and the applicability of a newly designed chromosomal probe for other Pelophylax taxa.

evolutionary biology↗

bioRxiv2023

Conserved satellite DNA motif and lack of interstitial telomeric sites in highly rearranged African Nothobranchius killifish karyotypes

Repetitive DNA may have significant impact on genome evolution. African annual killifishes of the genus Nothobranchius (Teleostei: Nothobranchiidae), which has adapted to temporary water pools in African savannahs, possess genomes with high repeat content. They are also characterized by rapid karyotype and sex chromosome evolution but the role of genome repeats in these processes remains largely unknown. Here, we analyzed the distribution of telomeric (TTAGGG)n repeat and Nfu-SatC satellite DNA (isolated formerly from N. furzeri) by fluorescence in situ hybridization in representatives across the Nothobranchius phylogeny (15 species), and with Fundulosoma thierryi as an outgroup. All analyzed taxa shared the presence of Nfu-SatC repeat but with diverse organization and distribution on chromosomes (from small clusters scattered genome-wide, to large localized accumulations, or a combined pattern). Nfu-SatC landscape was similar in conspecific populations of N. guentheri and N. melanospilus but slightly-to-moderately differed between populations of N. pienaari, and between closely related N. kuhntae and N. orthonotus. Inter-individual variability in Nfu-SatC patterns was found in N. orthonotus and N. krysanovi, including distinct segments present often in heterozygous condition. We revealed mostly no sex-linked patterns of studied repeats distribution in any of the sampled species including those with known sex chromosomes. Only in N. brieni (having an X1X2Y multiple sex chromosome system), Nfu-SatC probe covered substantial portion of the Y chromosome, similarly as formerly found in N. furzeri and N. kadleci (XY sex chromosomes), sister species not closely related to N. brieni. All studied species further shared patterns of telomeric FISH, with expected signals at the ends of all chromosomes and no additional interstitial telomeric sites. In summary, we revealed i) the presence of conserved satDNA class in Nothobranchius clade (a rare pattern among ray-finned fishes), ii) independent trajectories of Nothobranchius sex chromosome diferentiation, with recurrent and convergent accumulation of Nfu-SatC on the Y chromosome in some species, and iii) genus-wide shared propensity to loss of telomeric repeats during the mechanism of interchromosomal rearrangements. Collectively, our findings advance our understanding of genome structure, mechanisms of karyotype reshuffling and sex chromosome differentiation in Nothobranchius killifishes from the genus-wide perspective.

genetics↗

bioRxiv2023

Fast centromeric repeat turnover provides a glimpse into satellite DNA evolution in Nothobranchius annual killifishes

Satellite DNA (satDNA) is rapidly evolving class of tandem repeats with some motifs being involved in centromere organization and function. Rapid co-evolution of centromeric satDNA and associated proteins has been mostly attributed to the so-called centromere drive. To identify repeats associated with centromeric regions and test for the role of meiotic drive in their evolution, we investigated satDNA across Southern and Coastal clades of African annual killifishes of the genus Nothobranchius. C-banding showed expansion of (peri)centromeric heterochromatin regions in the Southern-clade killifishes. Molecular cytogenetic and bioinformatic analyses further revealed that two previously identified satellites, Nfu-SatA and Nfu-SatB, are associated with centromeres only in one lineage of the Southern clade. Nfu-SatB was, however, detected outside centromeres also in other members of the Coastal clade, which is consistent with the "library" hypothesis of satDNA evolution. We also identified a novel satDNA, Cl-36, associated with (peri)centromeres in N. foerschi, N. guentheri and N. rubripinnis from the Coastal clade. Our findings could be explained by centromere drive shaping karyotype change and centromeric repeat turnover in Nothobranchius species with possible reversal of spindle polarity within the Southern clade.

genetics↗

bioRxiv2022

Sex chromosome differentiation via changes in the Y chromosome repeat landscape in African annual killifishes Nothobranchius furzeri and N. kadleci

Repetitive DNA represents an important driver of sex chromosome differentiation. Yet, repetitive sequences tend to be misrepresented or overlooked in genomic studies. We analysed repetitive DNA landscape of sex chromosomes in several populations of a turquoise killifish Nothobranchius furzeri and its sister species N. kadleci (Teleostei: Nothobranchiidae), representatives of African annual killifishes with high rate of karyotype and sex chromosome evolution. We combined bioinformatic analyses of repeatome with molecular cytogenetic techniques such as comparative genomic hybridization, fluorescence in situ hybridization with satellite sequences, genes for ribosomal RNAs (rDNA) and bacterial artificial chromosomes (BACs) and immunostaining of SYCP3 and MLH1 proteins, which marked lateral elements of synaptonemal complexes and recombination sites, respectively. We revealed that N. furzeri and N. kadleci share the XY sex chromosome system, which is thus much older than previously assumed. Sex chromosomes are mostly heteromorphic as evidenced by distinct distribution of satellite DNAs and major rDNA. Yet, the heteromorphic XY sex chromosomes pair almost exclusively regularly in meiosis, which implies synaptic adjustment. Physical mapping of BACs identified inversions on Y chromosomes of the N. kadleci populations, akin to the pattern previously reported in N. furzeri. Yet, repetitive DNA landscape of X and Y sex chromosomes either diverged in parallel in populations of both species or it evolved in their common ancestor and thus predates the inversions. The observed differentiation via repeat repatterning thus cannot be explained by the classical sexually antagonistic model. Rather, we hypothesized that relaxed meiotic drive and recombination reduced by neutral processes could drive changes in repeatome and secondary inversions could be maintained by sexually antagonistic regulatory effects resulting from early evolution of dosage compensation. Author summaryEarly differentiation of sex chromosomes is not yet satisfactorily understood despite intensive research effort. Homomorphic sex chromosomes and their rapid turnover are common in teleost fishes, which makes them excellent models for studying evolution of nascent sex chromosomes. We investigated sex chromosomes in several populations of two sister species of African annual killifishes, Nothobranchius furzeri and N. kadleci, particularly their repetitive landscape, which was misrepresented in previous genomic studies. Combination of cytogenetic and genomic approaches revealed that both species share heteromorphic XY sex chromosome system. The N. furzeri XY sex chromosomes thus evolved earlier than previously expected. In N. kadleci, Y-linked inversions analogous to those reported in N. furzeri were detected. Changes in repetitive DNA distribution on sex chromosomes are either convergent or occurred in a common ancestor of both species, prior to the inversion events. The observed sex chromosome differentiation on repetitive DNA level thus cannot be reconciled with the classical theoretical model of sex chromosome evolution driven by sexually antagonistic selection. We invoke alternative explanations such as relaxed meiotic drive and recombination reduced by neutral processes, and we hypothesize that secondary inversions could be maintained by early evolution of dosage compensation resulting in sexually antagonistic regulatory effects.

evolutionary biology↗