Laboratory of Bioresource Regulation
In general, the mechanisms involved in developmental processes that are universal among organisms exhibit strong conservation. The idea that the knowledge obtained using model organisms is useful for understanding humans is also based on this major premise. "Sex" represented by males and females is also universally found in all multicellular organisms. However, the sex determination mechanisms between humans and Drosophila are completely different. Moreover, it has been found that sex-determining mechanisms differ even among closely related species. According to Cosmides and Tooby (1981), the sex-determining mechanism is full of meaningless complexity, incredibly sloppy, totally crazy, nothing more than waste from an individual standpoint. (Cosmides & Tooby, 1981). The essence of sexuality cannot be understood without clarifying why the sex-determing mechanism exhibits tremendous diversity.
Then, how many different gender formation mechanisms exist in nature? What kind of evolutionary process have the various gender formation mechanisms followed? Why is the evolution rate of the gender formation mechanism so fast? What are the factors that drive the evolution of the gender formation mechanism? By answering these questions, we can propose new biological significance of sex. In our research field, we challenge this question by conducting a wide range of analyzes from the cellular level to the individual level and the population level.
To answer this question, our laboratory is conducting research using insects as research materials. Because insects are the most diverse organisms on the earth and are said to be a treasure box of diversity. In our laboratory, we aim for a comprehensive understanding of various sex determination mechanisms for various insects and arthropods from Psocodea to Diptera, without sticking to model organisms.
Insects are generally small in size and prolific, and have a short life cycle, so they are a convenient research material for understanding evolutionary dynamics. In our laboratory, we find insect species that show regional polymorphisms in the function of sex-determining genes, and explore the mystery of how the diversity in their sex-determining mechanism has been created.
Our current research topics are as follows.
（１）Diversity of sex determination mechanisms created by the conflict between the host and symbiotic bacteria
Arthropods are infected with symbiotic bacteria such as Wolbachia and Spiroplasma, which bias the sex ratio of the host to females. Moreover, it has recently been found that Wolbachia directly interacts with the host's sex-determining genes and hijacks the sex-determining mechanism. To counter this hijacking, it is reasonable to imagine that various mutations will be introduced in the sex-determining genes on the host side. Using regional populations of the gypsy moth, which shows functional differences in sex-determining genes, as research material, we will examine the possibility that the regional differences found in sex-determining genes were acquired as a countermeasure against sexual manipulation by symbiotic bacteria.
（２）Diversity of sex determination mechanisms created by the conflict between males and females
While males and females cooperate with each other to leave offspring, there is a conflict in how to prioritize their own genes (male for males, female for females) and inherit them to the next generation. This conflict creates a unique sex determination system. Paternal Genome Elimination (PGE) is one of the sex determination systems that increase the reproductive value of females. In species that employ PGE, some maternal factor induces paternally-derived whole-genome inactivation, resulting in male determination. The paternal genome is not only inactivated, but also discarded during spermatogenesis. We will try to elucidate the molecular mechanism of PGE using booklices, Liposcelis sp. Elucidation of PGE will deepen the understanding of epigenetic modifications related to genomic imprinting and gene expression suppression mechanism associated with the epigenetic modifications.
（３）Search for missing links in sex determination mechanisms
There is little in common with the sex determination mechanisms of mammals and insects. Chelicerata (Arachnids) are phylogenetically located between mammals and insects. It has also been found that the developmental features of spiders are more similar to vertebrates. Elucidation of the sex determination mechanism of spiders may lead to the discovery of the missing link that connects the sex difference formation mechanism of mammals and insects. Focusing on this point, we aim to elucidate the sex determination mechanism of arachnids using the common house spider.
（４）To what extent are individual sex differences determined cell-autonomously?
Sex differences in mammals are said to be formed by the stimulation of sex hormones transported in the blood. However, recent studies have also revealed that individual cells autonomously undergo sexual differentiation depending on their own sex chromosomes. Such a cell-autonomous sex differentiation is widely recognized in insects. Then, to what extent are individual sex differences determined cell-autonomously? Our laboratory reveals this mystery by preparing cells from gynandromorphic silkworms, which consist of genetically male and female cells, and performing single-cell sequence analysis.