Every organism consists of small building blocks called cells. Different systems and organs are made up of various types of cells. For example, the primary cell type consists of neurons, which are highly specialized and represent a terminally differentiated cell population. Neurons are not present in the body from the beginning but appear at a certain stage of embryonic development. This phase is called neurogenesis. Neurons can be born as a result of either asymmetric or symmetric cell division. Asymmetric divisions result in two daughter cells with different fates (i.e., only one becomes a neuron), while daughter cells from symmetric divisions are identical. To study how these division modes are regulated, Ekaterina Dvorianinova's research used the zebrafish as a model organism.
Zebrafish share many similarities in neurogenesis with other vertebrates and allow for easy visualization of the process. Specifically, the research focuses on neurogenesis in the forebrain, a part of the zebrafish neural system that is evolutionarily related to the mammalian cortex. According to the findings, the first neurons are already present around 16 hours of age in the zebrafish forebrain. At this point, the primary mode of cell division is symmetric, where the mother cell gives rise to two neurons. Later, after 20 hours, the division mode shifts to asymmetric, where only one of the daughter cells differentiates into a neuron, and its sibling retains the properties of the mother progenitor cell.
Interestingly, the progenitor cells in the forebrain are also somewhat different: some divide faster, while others remain more inactive. “Families” derived from individual progenitor cells can also be described as varying from one another, with some containing more terminally differentiated cells compared to other clones with a more stem cell-like composition.
