Biology subjects

Nozawa, M.

Publications and source records attributed to Nozawa, M..

4 recordsLinked to original sources

bioRxiv2023

Evolution of sex-biased genes in Drosophila species with neo-sex chromosomes: potential contribution to reducing sexual conflict

An advantage of sex chromosomes is the potential to reduce sexual conflict because they provide a basis for selection to operate separately on females and males. However, evaluating the relationship between sex chromosomes and sexual conflict is challenging owing to the difficulty in measuring sexual conflict and substantial divergence between species with and without sex chromosomes. We therefore examined sex-biased gene expression as a proxy for sexual conflict in three sets of Drosophila species with and without young sex chromosomes, the so-called neo-sex chromosomes. In all sets, we detected more sex-biased genes in the species with neo-sex chromosomes than in the species without neo-sex chromosomes in larvae, pupae, and adult somatic tissues but not in gonads. In particular, many unbiased genes became either female- or male-biased after linkage to the neo-sex chromosomes in larvae, despite the low sexual dimorphism in larvae. However, sexual dimorphism at the adult stage can be a consequence of sexual conflict at the larval stage. For example, larval body size and rate of development are likely targets of sexually antagonistic selection (i.e., large size and rapid development are selected for in females but selected against in males). Indeed, genes involved in metabolism, a key determinant of the rate of development in many animals, were enriched in the genes that acquired sex-biased expression on the neo-sex chromosomes at the larval stage. These results indicate that acquiring neo-sex chromosomes may have contributed to a reduction in sexual conflict, particularly at the larval stage, in Drosophila. (247/250 words)

evolutionary biology↗

bioRxiv2023

Testing immediate dosage compensation by irradiation of heavy-ion beams to Drosophila miranda

Many organisms with heteromorphic sex chromosomes have a mechanism of dosage compensation (DC) in which X-linked genes are upregulated in males to mitigate dosage imbalance between sexes and between chromosomes. However, how quickly the DC is established during evolution remains elusive. In this study, irradiating the heavy-ion beams to Drosophila miranda that have young sex chromosomes, the so-called neo-sex chromosomes, we induced deletions on the neo-Y chromosome to mimic the situation of Y-chromosome degeneration in which functional neo-Y-linked genes were just nonfunctionalized and tested if their neo-X-linked gametologs were immediately upregulated. Since the males with the 2-Gy irradiation of iron-ion beam showed a lower fertility, we sequenced the genomes and transcriptomes of six F1 males derived from these males. Our pipeline identified 82 neo-Y-linked genes in which deletions were predicted in the F1 males. However, all but three of them had paralogs in addition to their neo-X-linked gametologs. Moreover, candidate deletions in the remaining three genes that showed one-to-one gametologous relationship with the neo-X-linked genes occurred in UTRs and did not affect the expression levels of these genes. Therefore, we were unable to directly evaluate whether DC immediately operated on the neo-X-linked genes in response to the disruption of their neo-Y-linked gametologs. Yet, our observation that the deletions occurred less frequently in one-to-one gametologs indirectly suggests that DC unlikely operated on the neo-X-linked genes immediately after the pseudogenization of their neo-Y-linked gametologs in D. miranda. Therefore, dosage imbalance due to deletions in the neo-Y-linked genes without paralogs may not have effectively been compensated and individuals with such deletions could have become lethal. We speculate that the neo-sex chromosomes in D. miranda may be too young to establish the immediate DC. Future studies on sex chromosomes with different ages will further evaluate our tentative conclusion.

evolutionary biology↗

bioRxiv2023

Direct link between convergent evolution at sequence level and phenotypic level of septal pore cap in Agaricomycotina

Several apparently homologous morphological characters are known to have independently evolved in different lineages multiple times. However, the genetic backgrounds of such morphological convergences are not well understood. To detect any correlated genes potentially responsible for morphological convergence at the phenotypic level, we focused on the morphology of the septal pore cap (SPC), which is involved in mycelias complex multicellularity in fungi. SPCs are classified into three morphological types: perforate, imperforate, and vesiculate. To understand what evolutionary events occurred at the sequence level during morphological convergence of perforate SPCs in Agaricomycotina, we examined sequence differences between species with different SPC types by comparative genomic analysis. If sequences from species with perforate SPCs formed a cluster, the associated gene might be involved in generating perforate SPCs in multiple lineages. Based on this assumption, we detected eight candidate genes, including an SPC-related gene, spc33. The results showed that some amino acid substitutions independently occurred in both lineages in which species with perforate SPCs emerged. From these results, we speculate that the amino acid substitutions in spc33 were critical in the emergence of perforate SPCs in multiple lineages. We also found that spc33 evolved just before imperforate SPC emergence based on homology search of spc33 and the species phylogeny. These findings illustrate the first step to clarifying the genetic basis of SPC morphological evolution. Our study contributes to both clarifying the genetic basis of morphological convergence and pioneering our understanding of fungal evolutionary morphology.

evolutionary biology↗

bioRxiv2021

Evolutionary trajectories of three independent neo-sex chromosomes in Drosophila

Dosage compensation (DC) on the X chromosome is a mechanism to counteract the deleterious effects by gene loss from the Y chromosome. However, DC cannot work efficiently if the X chromosome also degenerates. This indeed occurs in the neo-sex chromosomes in Drosophila miranda, where neo-X as well as neo-Y chromosomes are under accelerated pseudogenization. To examine the generality of this pattern, we investigated the evolution of two additional neo-sex chromosomes that independently emerged in D. albomicans and D. americana and compared their evolutionary processes with that in D. miranda. Comparative genomic and transcriptomic analyses revealed that the pseudogenization rate on neo-X is also accelerated in the two species (though lesser extent in D. americana). We also found that neo-X-linked genes whose neo-Y homologs are pseudogenized tend to be upregulated more stringently than those whose neo-Y homologs remain functional. Moreover, the genes under strong functional constraints and highly expressed in the testis tended to remain functional on neo-X and neo-Y, respectively. Focusing on the D. miranda and D. albomicans neo-sex chromosomes that independently emerged from the same autosome, we further found that the same genes tend to have been pseudogenized in parallel on neo-Y. Those genes include Idgf6 and JhI-26 whose functions seem to be unnecessary or could be even harmful for males. These results indicate that neo-sex chromosomes in Drosophila share a common evolutionary trajectory after their emergence, which may be applicable to other sex chromosomes in a variety of organisms to avoid being an evolutionary dead-end.

evolutionary biology↗