How do chromosomes divide?
In a body, every single cell has the same number of chromosomes. This is because when a cell divides, the replicated chromatids are equally segregated into daughter cells. But, the first meiotic division is a clear exception. This division segregates maternal and paternal chromosomes for production of eggs and sperms, which are the origin of a new life. What is the story behind this division?
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News
30 April, 2026
Cytoplasmic competition between pronuclei supports early embryonic development
In mammalian zygotes, maternal and paternal genomes are enclosed in separate pronuclei. Here, we show that these pronuclei compete for limited cytoplasmic factors, which constrains nuclear size and maintains proper epigenetic states. When both genomes are combined into a single pronucleus, this competition is lost, leading to nuclear enlargement, epigenetic dysregulation, and reduced developmental potential. These findings demonstrate that pronuclear separation is a fundamental mechanism supporting early embryonic development.
Kyogoku H, Tarama M, Matsuwaka M, Mishina T, Harada A, Nakagawa R, Kumon M, Shimizu Y, Ohkawa Y, Shibata T, Inoue A, Kitajima TS, "Cytoplasmic competition between separate parental pronuclei in zygotes", Nature, doi:10.1038/s41586-026-10417-7.
22 April, 2026
Live imaging of mammalian oocyte formation
In mammals, oocyte formation occurs within the fetus, and thus its process have remained largely elusive. In this study, we have established a technique for ex vivo culture of mouse fetal gonads combined with optical live imaging. Using this technique, we discovered stage-specific membrane blebbing of germ cells. Moreover, we observed no detectable intercellular transfer of organelles, unlike non-mammalian species, suggesting the existence of a mammal-specific mechanism underlying oocyte formation.
Aizawa E, Shimamoto S, Kajikawa E, Hara J, Abe T, Shibuya H, Kitajima TS, "Dynamic blebbing and absence of organelle transfer
during mouse oocyte formation", The EMBO Journal, doi:10.1038/s44318-026-00780-6.
21 April, 2026
Mitotic Spindle: From living and synthetic systems to theory
At Mitotic Spindle:
From living and synthetic systems to theory, held in Dubrovnik, Croatia, from April 12 to 15, 2026, Tomoya Kitajima delivered an invited lecture.
10 April, 2026
Welcome party
We held a welcome party to celebrate Tao Pan, Tae Akizuki, and Mizuki Morihashi joining our lab.
Upcoming Events
12 May, 2026
31 May - 3 June, 2026
International Symposium on Chromosome Dynamics： from Structure to Cellular Function
9 June - 12 June, 2026
The 59th Annual Meeting of the Japanese Society of Developmental Biologists