No abstract

Kings and queens of termites, like queens of other advanced eusocial insects, are endowed with admirable longevity, which dramatically exceeds the life expectancies of their non-reproducing nest-mates and related solitary insects. In the quest to find the mechanisms underlying the longevity of termite reproductives, we focused on somatic maintenance mediated by telomerase. This ribonucleoprotein is well established for pro-longevity functions in vertebrates, thanks primarily to its ability of telomere extension. However, its participation in lifespan regulation of insects, including the eusocial taxa, remains understudied. Here, we report a conspicuous increase of telomerase abundance and catalytic activity in the somatic organs of primary and secondary reproductives of the termite Prorhinotermes simplex and confirm a similar pattern in two other termite species. These observations stand in contrast with the telomerase downregulation characteristic for most adult somatic tissues in vertebrates and also in solitary insects and non-reproducing castes of termites. At the same time, we did not observe caste-specific differences in telomere lengths that might explain the differential longevity of termite castes. We conclude that although the telomerase activation in termite reproductives is in line with the broadly assumed association between telomerase and longevity, its direct phenotypic impact remains to be elucidated.

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.

http://www.eje.cz cused on chromosomal races of the obligatory parthenogenetic species Pycnoscelus surinamensis (Linnaeus, 1758) and its bisexual ancestor Pycnoscelus indicus (Fabricius, 1775) (Matthey, 1945(Matthey, , 1948Roth, 1967;Roth & Cohen, 1968) and the description of chromosome numbers and spermatogenesis in other species of cockroaches (Piza, 1958). Signifi cant attention was also given to chromosomal mutations resulting in formation of autosomal multivalents in

No abstract

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 repeat's 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.

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.