Mouse-derived cerebral organoids as a tool for investigating the role of Foxg1 in forebrain development
Marshall, Jonathon Jay
The formation of the mammalian forebrain is a highly complex process requiring the precise interplay of numerous factors. One such factor is the gene Foxg1 which begins to be expressed at the very earliest stages of telencephalic development, it has been linked to numerous processes including controlling cell cycle kinetics and patterning of the ventral telencephalon. The aim of this thesis is to use mouse embryonic stem cells to created cerebral organoids with wildtype, Foxg1-/- and Foxg1-/+ genotypes. The results showed that progenitors in Foxg1-/- cerebral organoids had a slight but statistically insignificant premature elongation of the cell cycle. For wildtype the cell cycle at day 7 of the protocol was estimated at 22.3 hours, for the null mutant cells cycle was calculated as 26.2 hours. However, important to note the values for cell cycle were not the same as in vivo, highlighting the differences between to two systemns. Furthermore, when investigating the requirement for Foxg1 in the ventral telencephalon this was impeded by the fact cerebral organoids appeared to default to a cerebral cortical fate. On average 7.8%, SEM = ± 4.4% of telencephalic tissue within the cerebral organoids under the original protocol conditions became ventral telencephalon. However, they could be directed to adopt a more ventral telencephalic fate by activation of the sonic hedgehog pathway. This led to an average of 33.8%, SEM = ± 6.5% of telencephalic tissue in these organoids adopting a ventral telencephalic fate. When Foxg1-/- stem cells were put through this ventral protocol they failed to form ventral telencephalon, as seen in vivo. These results highlight that overall cerebral organoids successfully recapitulate some key aspects of the Foxg1-/- phenotype, such as the lack of ventral telencephalic tissue being formed. However, they also show some important differences between organoids and in vivo, including the differences in cell cycle lengths which did not show the level of differentiation in organoids as would be expected in vivo. This suggests that the kinetics of cells and the phenotypes seen in organoids may well be different to in vivo and as such this should be taken into account for future experiments.