06. 02. 2026
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A new review study by reproductive biologist Helena Fulková, recently published in the journal Reproduction (IF 3,7) (open in a new window), offers a new perspective on the role of the tiny structures, so-called nucleolus precursor bodies, in the nucleus of a human zygote. The authors show that previous research has focused primarily on their number and arrangement, while overlooking their dynamics. However, it is precisely this that proves to be key to understanding early embryo development. The study was carried out in collaboration with scientists from the University of Teramo and the Institute of Animal Science.
Even before the human embryo divides for the first time, subtle but fundamental processes take place within it. Immediately after fertilisation, a single cell – the zygote – is formed, which carries all the information necessary for the creation of a new organism. It is at this stage that inconspicuous structures appear in its nuclei, which scientists have been paying increasing attention to in recent years, and this new study places them in a broader biological context.
What happens after fertilisation?
The zygote contains two separate nuclei: one from the mother’s egg and one from the father’s sperm. Each contains several small round structures known as nucleolus precursor bodies. These structures differ from the nucleoli we know from other cells in the body, and it has long been assumed that they play a rather passive role. However, the new study summarises the current knowledge and suggests that this interpretation was too simplistic and does not capture the true significance of these structures.
When number and arrangement matter
Previous research has shown that embryos in which the nucleolar precursors in both nuclei have a similar number and uniform distribution are more likely to develop further. Conversely, an irregular arrangement of these structures may be associated with poorer prospects for the embryo. These differences can be observed very early on, even before the first cell division.
However, a new review highlights a poorly researched aspect: the movement of embryonic nucleoli within the nucleus. The authors summarise findings from previous studies, based on time-lapse microscopy and other experimental approaches, suggesting that faster movement is typically associated with embryos with the correct number of chromosomes, while slower dynamics are more common in embryos with genetic abnormalities.
The study also shows that the mechanisms underlying the different speeds of nucleolar movement have not yet been elucidated. Neglected factors include the influence of the cell nucleus’s internal structure, the cell’s energy state, and other regulatory mechanisms. These questions also represent an important direction for further basic research.
Why is this important?
The study shows that even in the first moments of the creation of life, there is a surprisingly complex and dynamic organisation that cannot be described by static parameters alone. This new perspective on the behaviour of embryonic nuclei expands our current understanding of early embryonic development and helps us better understand how a healthy organism is formed and why development sometimes stops at the very beginning.