Integrated Biology Laboratories

Germline Biology Group

Prof. KAI Toshie Prof. KAI Toshie


Non-coding RNA, small RNA, Germline cell, Gametogenesis, Drosophila melanogaster

Unveiling the secret of germline cells

Although individual animals do die, the species is maintained by producing the next generation through active sexual reproduction. Individuals are just like vehicles in which passengers -genetic information– can ride to be inherited by the next generation through germline lineage. As such, germline cells are the most important cells to maintain the species. Drosophila melanogaster is one of the ideal model organisms where we can easily study gametogenesis. How are germline stem cells maintained in a microenvironment,niche? What is the molecular mechanism that controls differentiation of germline cells to eggs and sperm? How are germline genomes safely guarded by non-coding RNA called piRNA from transposons attacks? How are the piRNAs generated in membrane-less organelle called nuage? Our group has been addressing such molecular mechanisms for the better understanding of gametogenesis.

Tejas (fly homolog of Tdrd5) localizes to a membrane-less organelle called nuage at the periphery of the nucleus of germline cells, and functions in the production of piRNAs.


Toshie Kai (Professor) toshie_kai[at]
Taichiro Iki (Associate Professor) ikit[at]
Shinichi Kawaguchi (Assistant Professor) shinkawa[at]
Ritsuko Suyama (Specially Appointed Assistant Professor) rrsuyama[at]
Chisato Yanagisawa (Technical Assistant&Secretary)  

You could probably reach more information of individual researchers by Research Map and researcher's search of Osaka-U.

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What is your hot research topic?
Genomes in germline cells that differentiate into gametes are inherited by the next generation, and gene expression is tightly regulated by epigenetic control. Currently, we are analyzing not only non-coding RNA and RNA modification, but also function of nuage, a membrane-less organelle that is specific to germline cells. We are excited by the unexpected discoveries of the secrets of germline cells.
What kind of background do your lab members have?
The laboratory staff has backgrounds in biochemistry and genetics, and long experience of studying abroad. Since the lab opened in 2015, the number of PhD students has gradually increased, but at first only staff. While in Singapore, PhD students were the main lab members and we had only one postdoc. These individuals were from India, China, Singapore, France, and Malaysia. The current lab at FBS also has a high proportion of international students, so the main language in the lab is English.
Do you collaborate with other institutions and universities?
Because I spent many years overseas, I have many friends and former colleagues all over the world. Hence there are many opportunities for international collaborations based on long-standing relationships. We have international collaborations with the labs at the National University of Singapore, the University of Hawaii, and in Japan, Tokyo University and NIBB.
What kind of careers do your Lab's alumni go on to?
Two former PhD students became PIs in academic labs in Singapore and India, respectively. Others became senior researchers in India and Singapore. There is one teaching science in one of the top junior high schools in Singapore. The graduate students I supervised in OU got positions at the Scientific Research Institute.

Research Highlights

Publications (Research Articles, Reviews, Books)


Ritsuko Suyama, Nicolas Cetraro, Joanne Y Yew, Toshie Kai

Microbes control Drosophila germline stem cell increase and egg maturation through hormonal pathways

Commun. Biol. 6(1):1287  2023 PMID:38123715 DOI:10.1038/s42003-023-05660-x

Yuxuan Lin, Ritsuko Suyama, Shinichi Kawaguchi, Taichiro Iki, Toshie Kai

Tejas functions as a core component in nuage assembly and precursor processing in Drosophila piRNA biogenesis

J. Cell Biol. 222(10):e202303125  2023 PMID:37555815 DOI:10.1083/jcb.202303125

Iki T, Kawaguchi S, Kai T

miRNA/siRNA-directed pathway to produce noncoding piRNAs from endogenous protein-coding regions ensures Drosophila spermatogenesis

Science Advances Vol. 9, No. 29  2023 PMID:37467338 DOI:10.1126/sciadv.adh0397


*Lim L-X, *Isshiki W, Iki T, Kawaguchi S, Kai T *Co-first authors

The Tudor-domain containing protein, Kotsubu (CG9925), localizes to the nuage and functions in piRNA biogenesis in D. melanogaster

Frontiers in Molecular Biosciences (section RNA Networks and Biology) Vol. 9, Article 818302  2022 PMID:35425810 DOI:10.3389/fmolb.2022.818302


Suyama R, Kai T (equal corresponding author)

Review: Non-membranous RNP condensates control the fate of germline cells

Jikken-igaku special issue Vol. 39, No. 10  2021


Taichiro Iki, Moe Takami, Toshie Kai

Modulation of Ago2 Loading by Cyclophilin 40 Endows a Unique Repertoire of Functional miRNAs During Sperm Maturation in Drosophila

Cell Rep. Vol. 33, No. 6, 108380  2020 PMID:33176138 DOI:10.1016/j.celrep.2020.108380

Kai Wang, Ryo Tomura, Wei Chen, Miho Kiyooka, Hinako Ishizaki, Tomoyuki Aizu, Yohei Minakuchi, Masahide Seki, Yutaka Suzuki, Tatsuya Omotezako, Ritsuko Suyama, Aki Masunaga, Charles Plessy, Nicholas M Luscombe, Christelle Dantec, Patrick Lemaire, Takehiko Itoh, Atsushi Toyoda, Hiroki Nishida, Takeshi A Onuma

A genome database for a Japanese population of the larvacean Oikopleura dioica

Dev. Growth Differ. Vol. 62, No. 6, 450-461  2020 PMID:32677034 DOI:10.1111/dgd.12689

Shinichi Kawaguchi, Mizuki Ueki, Toshie Kai

Drosophila MARF1 ensures proper oocyte maturation by regulating nanos expression

PLoS ONE Vol. 15, No. 4, e0231114  2020 PMID:32243476 DOI:10.1371/journal.pone.0231114

Garth R. Ilsley, Ritsuko Suyama, Takeshi Noda, Nori Satoh, Nicholas M. Luscombe

Finding cell-specific expression patterns in the early Ciona embryo with single-cell RNA-seq

Sci. Rep. 10:4961-4970  2020 PMID:32188910 DOI:10.1038/s41598-020-61591-1

Ryusuke Niwa, Toshie Kai

Editorial overview: Stem cells orchestrate oogenesis: a lesson from the fruit fly, Drosophila melanogaster.

Curr. Opin. Insect Sci. 37:1-62  2020 PMID:32199590 DOI:10.1016/j.cois.2020.03.001


Derrien B, Clavel M, Baumberger N, Iki T, Sarazin A, Hacquard T, Ponce MR, Ziegler-Graff V, Vaucheret H, Micol JL, Voinnet O, Genschik P

A Suppressor Screen for AGO1 Degradation by the Viral F-Box P0 Protein Uncovers a Role for AGO DUF1785 in sRNA Duplex Unwinding

Plant Cell 30(6):1353-1374  2018 PMID:29848768 DOI:10.1105/tpc.18.00111

Iki T, Cl&eaute;ry A, Bologna NG, Sarazin A, Brosnan CA, Pumplin N, Allain FHT, Voinnet O

Structural Flexibility Enables Alternative Maturation, ARGONAUTE Sorting and Activities of miR168, a Global Gene Silencing Regulator in Plants

Mol. Plant. 11(8):1008-1023  2018 PMID:29803952 DOI:10.1016/j.molp.2018.05.006

Teo RYW, Anand A, Sridhar V, Okamura K, Kai T

Heterochromatin protein 1a functions for piRNA biogenesis predominantly from pericentric and telomeric regions in Drosophila

Nat. Commun. 9(1):1735  2018 PMID:29728561 DOI:10.1038/s41467-018-03908-3

Gleason RJ, Anand A, Kai T, Chen X

Protecting and diversifying the germline.

Genetics 208(2):435-471  2018 PMID:29378808 DOI:10.1534/genetics.117.300208


Iki T, Ishikawa M, Yoshikawa M

In vitro formation of plant RNA-induced silencing complexes using as extract of evacuolated tobacco protoplasts

Methods Mol Biol 1640:39-53  2017 DOI:10.1007/978-1-4939-7165-7_3

Tschopp MA, Iki T, Brosnan CA, Jullien PE, Pumplin N

A complex of Arabidopsis DRB proteins can impair dsRNA processing.

RNA 23(5):782-797  2017 PMID:28232389 DOI:10.1261/rna.059519.116

Iki T, Tschopp MA, Voinnet O

Biochemical and genetic functional dissection of the P38 viral suppressor of RNA silencing.

RNA 23(5):639-654  2017 PMID:28148824 DOI:10.1261/rna.060434.116

Iki T

Messages on Small RNA Duplexes in Plants

J. Plant Res. 130(1):7-16  2017 PMID:27878651 DOI:10.1007/s10265-016-0876-2


Qu&eaute;nerch'du E, Anand A, Kai T

The piRNA pathway is developmentally regulated during spermatogenesis in Drosophila.

RNA 22(7):1044-54  2016 PMID:27208314 DOI:10.1261/rna.055996.116

Yoshikawa M, Iki T, Numa H, Miyashita K, Meshi T, Ishikawa M

A Short Open Reading Frame Encompassing the MicroRNA173 Target Site Plays a Role in trans-Acting Small Interfering RNA Biogenesis

Plant Physiol. 171(1):359-368  2016 PMID:26966170 DOI:10.1104/pp.16.00148

Our ideal candidate (as a graduate student)

Kai Laboratory is looking for students dedicated to the stuides addressing the mystery of germline cells.

FBS is a very advanced research/educational institution that attracts diverse researchers. FBS has well equipped common facilities and ooffers a variety of learning oppoorunites.The graduate students are very well supported. If you wish to enrol, please refer the information about the entrance examination of FBS and contact the Kai-lab staff.

Prof Kai has supervised many PhD students and interns at Canegie Institution, National University of Singapore and Nanyang Technological University. Taking advantage of her long experience in research in USA and Singapore, we hope to contribute to global human resources.

If you would like to participate the lab as a postdoctoral researcher, please do not hesitate to contact the Kai-lab staffs.


Germline Biology Group, Graduate School of Frontier Biosciences, Osaka University,
1-3 Yamadaoka, Suita, Osaka 565-0871 Japan.

TEL: +81-6-6879-7974

E-mail: toshie_kai[at] (Prof. Toshie Kai)

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