Suppression of Oct4 by Germ Cell Nuclear Factor Restricts Pluripotency and Promotes Neural Stem Cell Development in the Early Neural Lineage

The earliest mouse neural stem cells (NSCs) depend on a factor called leukemia inhibitory factor (LIF) and exhibit unique characteristics. They can change into different cell types but eventually specialize into definitive neural stem cells (dNSCs) by around embryonic day 7.5. This transition is accompanied by a reduction in their ability to become other cell types. In this study, we explored how a protein called germ cell nuclear factor (GCNF) controls the expression of Oct4, a critical gene for maintaining the stem cell's abilities. We discovered that GCNF suppresses Oct4, which is critical for NSC maturation. Without GCNF, the transition to dNSCs is impaired, highlighting the importance of Oct4 regulation in NSC development.

During early development in mice, primitive neural stem cells (pNSCs) can be isolated and are still able to develop into a variety of cell types. However, by around embryonic day 7.5, these cells must progress to a more specialized state (dNSCs). It's known that Oct4 plays a significant role in maintaining a cell's ability to transform (pluripotency), but the exact mechanisms affecting these transitions in NSCs are poorly understood.

In this study, we examined the role of GCNF, which is known to suppress Oct4 during early neural development. Our focus was to understand the impact of GCNF on the transition from pNSCs to dNSCs, emphasizing Oct4 suppression's importance in maintaining the cell's identity and its development.

We found that Oct4 is initially present in pNSCs but decreases as these cells mature into dNSCs. Specifically, GCNF acts to suppress Oct4 levels at strategic points in development, which is essential for the transition to dNSCs. When GCNF is absent, Oct4 levels remain high, preventing this critical transition.

In mouse embryos lacking GCNF, we observed that while pNSCs continue to proliferate, their ability to transition into dNSCs is drastically reduced. This indicates that GCNF is essential for facilitating the maturation necessary for NSCs to become more specialized.

Despite efforts to advance the differentiation of GCNF-deficient NSCs, these cells showed sustained Oct4 expression, suggesting they might be stuck in an immature state. This persistence of Oct4 likely restricts their maturation and subsequent ability to effectively contribute to the nervous system.

We further analyzed the molecular changes occurring during the transition from pNSCs to dNSCs. GCNF was shown to induce specific epigenetic modifications to the Oct4 gene, resulting in its long-term suppression. This suppression is crucial for maintaining the function and limits of NSCs.

Overall, our findings underscore the critical role of GCNF in controlling the fate of early neural stem cells through Oct4 regulation. This process is essential for guiding stem cells from a primitive state that can become many different cell types to a definitive state focused on producing neural tissue.

Regulating GCNF and Oct4 is vital for neural development in early embryogenesis, with implications for regenerative medicine. Manipulating these factors could enhance stem cell therapies aimed at repairing nervous system damage or counteracting age-related decline.