Biology subjects

Sahara, K.

Publications and source records attributed to Sahara, K..

5 recordsLinked to original sources

bioRxiv2024

Transposon fusion gave birth to Fem, Bombyx mori female determining gene

Fem is a W-linked piRNA precursor, and Fem piRNA is a master gene of female determination in Bombyx mori. Since Fem has significantly low similarity to any known sequences and the origin of Fem remains unclear, two hypotheses have been proposed for the origin of Fem. The first one is that Fem is an allele of Masc, while the second one is that Fem arose by transposition of Masc. To draw a solid conclusion, we determined the W chromosome sequences of B. mori and a closely relative bombycid species of Trilocha varians with a Fem-independent sex determination system. Comprehensive genome comparison led us to the "third" hypothesis: Fem is a chimeric sequence of transposons. Although we still cannot completely exclude the first hypothesis, at least a large portion of the parts other than the 44-bp Masc similarity region is derived from transposons, and even the 44-bp region could correspond to the boundary of the two transposons, gypsy and satellite DNA.

genetics↗

bioRxiv2023

Ghost W chromosomes and unique genome architecture in ghost moths of the family Hepialidae

The classical model of sex chromosome evolution has been recently challenged in moths and butterflies (Lepidoptera). According to the current hypothesis, the adoption of a supernumerary chromosome may have driven the transition from the Z0 to the WZ sex chromosome system in females. However, the evolutionary history of the W chromosome remains enigmatic, especially in the early-diverging lepidopteran lineages. In ghost moths of the family Hepialidae, one of the most basal lepidopteran clades, there is conflicting evidence regarding their sex chromosomes. In this study, we aimed to clarify the status of the hepialid W chromosome. Using cytogenetics and genomics, we investigated the karyotype, sex chromosomes, genome size and repeatome of multiple ghost moth species and reconstructed basic phylogenetic relationships in the group. Our data show that Hepialidae have unusually large genomes (reaching up to 1C = 3 Gb) and are the oldest known lepidopteran clade with a W chromosome. However, the W does not form a typical heterochromatin body in polyploid nuclei, known as sex chromatin, previously employed to detect the presence of W chromosomes across Lepidoptera. Moreover, in some species, the W does not exhibit distinct repeat content and can escape detection via methods that rely on W-specific sequences. Analysis of the Z chromosome confirmed highly conserved gene content, arguing for a possible origin of the hepialid W chromosome from a B chromosome. We hypothesize that the mechanism underlying the formation of sex chromatin could be used in future research to study the origin of the W chromosome.

genomics↗

bioRxiv2023

Multiple sex chromosomes of Yponomeuta ermine moths suggest a role of sexual antagonism in sex chromosome turnover in Lepidoptera

Sex chromosome-autosome fusions give rise to neo-sex chromosomes, which provide an insight into early evolution of sex chromosomes and drivers of chromosomal fusions. While sex chromosome-autosome fusions are scarce in vertebrates with female heterogamety ([female]ZW/[male]ZZ), they are common in moths and butterflies (Lepidoptera), the most species rich group with heterogametic females. This contradicts theoretical model that assumes chromosome fusions to be random and predicts them to be rare in taxa with high chromosome number such as Lepidoptera. In the present study we analyzed sex chromosomes in nine ermine moths of the genus Yponomeuta (Yponomeutidae) and their two outgroups, Teinoptila gutella (Yponomeutidae) and Plutella xylostella (Plutellidae). We employed genomic in situ hybridization to identify sex chromosomes and used a custom designed microarray to identify Z-linked genes. Our results confirmed a multiple sex chromosome system Z1Z2W to be present in T. gutella and all Yponomeuta spp. except for Y. tokyonella. The multiple sex chromosome system resulted from a fusion between the W chromosome and autosome homeologous to the Bombyx mori chromosome 2 (BmChr2). The BmChr2 bears a cluster of genes with ovary-specific expression which suggests that sexually antagonistic selection could have driven fixation of the fusion in a common ancestor of Yponomeuta and Teinoptila genera. We hypothesize that sex chromosome turnover in Lepidoptera could be driven by sexual antagonism.

evolutionary biology↗

bioRxiv2023

Lepidopteran Synteny Units (LSUs) reveal deep conservation of macrosynteny in butterflies and moths

Advances in DNA sequencing technologies have, for the first time, provided us with enough whole chromosome-level genomes to understand in detail how chromosome number and composition change over time. Here, we use the genomes of butterflies and moths to look at the levels and age of macrosynteny in the Lepidoptera and Trichoptera. We used comparative BUSCO analsysis to define reproducible units of macrosynteny which we term Lepidopteran Synteny Units or LSUs. The 31 chromosomes of the model butterfly Melitaea cinxia served as a reference point. The results show that chromosome-wide macrosynteny extends from the most basal branches of the Lepidopteran phylogeny to the most distal. This synteny also extends to the order Trichoptera, a sister group of the Lepidoptera. Thus, chromosome-wide macrosynteny has been conserved for a period of >200 My in this group of insects. We found no major interchromosomal translocations, reciprocal or non-reciprocal, in the genomes studied. Intrachromosomal rearrangements, in contrast, were abundant. Beyond its use in defining LSUs, this type of homology-based analysis will be useful in determining the relationships between chromosomal elements in different animals and plants. Further, by more precisely defining the breakpoints of chromosomal rearrangements we can begin to look at their potential roles in chromosomal evolution. StatementThe authors declare no conflicting interests ContributionsConceptualisation: W.T., R.H.f.; data analysis: W.T.; writing & editing: W.T., K.S., R.H.f All authors read and approved the final manuscript.

genomics↗

bioRxiv2017

Master manipulation continued: feminizing Wolbachia endosymbiont distorts sex chromosome inheritance

Genomes are vulnerable to selfish genetic elements that enhance their own transmission often at the expense of host fitness. Examples are cytoplasmic elements such as maternally inherited bacteria that cause feminization, male-killing, parthenogenesis and cytoplasmic incompatibility. We demonstrate, for the first time, that segregation distortion, a phenomenon so far seen only for nuclear genetic elements, can also be caused by a cytoplasmic element, the ubiquitous endosymbiotic bacterium Wolbachia. For Eurema mandarina butterfly lineages with a Z0 sex chromosome constitution, we provide direct and conclusive evidence that Wolbachia induces production of all-female progeny by a dual role: the compensation for the female-determining function that is absent in Z0 lineages (feminization) and the prevention of maternal sex chromosome inheritance to offspring as a specific type of segregation distortion. Therefore, our findings highlight that both sex determination and chromosome inheritance -- crucially important developmental processes of higher eukaryotes -- can be manipulated by cytoplasmic parasites.

evolutionary biology↗