The role of TAp73 in neurodevelopment

The transcription factor P73 belongs to the p53 protein family, and its gene encodes two main isoforms: the transcriptionally active TAp73 isoform and the dominant-negative ΔNp73. Both isoforms play pivotal roles in regulating the self-renewal and differentiation of neural stem/progenitor cells, thus play a critical role in brain development during neuronal differentiation. Mutations in TP73 are associated with lissencephaly in humans and severe brain defects in mice. The role of TP73 and its isoforms during neurogenesis in human is still unclear. Aiming to further scrutinize the role of TAP73 in corticogenesis and neurodevelopment in humans, we generated forebrain organoids derived from human induced pluripotent stem cells carrying a TAP73 LOF mutation generated by CRISPR-Cas. Using immunoblotting and immunofluorescence analyses, we examined forebrain organoids collected at different developmental stages to identify neural progenitors such as radial glia cells, intermediate progenitors, as well as neurons. Our findings indicate that, TAP73-organoids displayed less progenitor cells and a higher proportion of differentiated cells at day 40 than control organoids, suggesting an early differentiation pattern. Additionally, we evaluated proliferation in control and TAP73-organoids using immunofluorescence with anti-PHH3. Overall, TAP73-organoids exhibit reduced proliferative activity, and the expression pattern of PHH3 differed from that of the control. In conclusion, our results suggest that the differentiation/proliferation processes are disrupted in TAP73-organoids compared to control organoids, consistent with impaired cortical development. Investigating the roles of TP73 isoforms can enhance our understanding of the underlying mechanisms contributing to TP73-associated neurodevelopmental disorders in humans, such as lissencephaly.