KAP1-Paupar lncRNA chromatin regulatory complex controls subventricular zone neurogenesis

Neurogenesis continues postnatally in two major neural stem cell (NSC) niches, the subventricular zone (SVZ) and dentate gyrus of the hippocampus. NSCs in the SVZ exhibit some biological features of glia, especially astrocytes. However, it is still not clear how NSCs in the SVZ can maintain stem cell self-renewal properties and the potential to generate transit amplifying progenitor cells (TAPs) that give rise to neuroblasts. Neuroblasts migrate through the rostral migratory stream (RMS) to the olfactory bulbs where they differentiate into neurons. In this project, I investigated the function and mode of action of a new KAP1-lncRNA chromatin regulatory complex in the control of postnatal and adult neural stem cell (NSC) self-renewal and neurogenesis.
KAP1 is an important epigenetic regulatory protein that is required for embryonic brain development and adult brain function. I have demonstrated a broad expression of KAP1 in the normal postnatal/adult SVZ neurogenic lineage. I then uncovered for the first time that KAP1 influences postnatal and adult SVZ-OB neurogenesis. I showed that KAP1 is important for SVZ NSC identity maintenance, and functions to protect NSCs from mature astrocytic fate. In addition, KAP1 loss-of-function reduced the number of newborn neurons in the olfactory bulb and delayed their morphological differentiation. On the molecular level, I showed that KAP1 regulates the expression of members of the BMP signalling pathway to control SVZ NSCs maintenance and lineage commitment.
LncRNAs are a new class of regulatory molecules thought to be important in brain development and function. Several thousand lncRNAs are expressed in the SVZ, yet only a very small number have been studied and shown to have function in vivo. Nuclear lncRNAs act as regulators of gene expression and many of these bind chromatin regulatory complexes. They may act either as guides to recruit associated proteins to their target genes or molecular scaffolds to control ribonucleoprotein complex assembly and function. Here, I show that KAP1 physically interacts with the lncRNA Paupar, a CNS expressed and chromatin-associated lncRNA that is transcribed upstream of the gene encoding the Pax6 transcription factor, in the SVZ. This was similar to the N2A cell line where Paupar, KAP1 and Pax6 together form a ribonucleoprotein complex (Pavlaki et al., 2018).
Interestingly, I found that even though KAP1 and Paupar showed a similar phenotypic result of reduction in the number of neurons arriving to the OB, they displayed a different functional role in regulating NSC behaviour in the SVZ. This suggests that even if they exist in the same ribonucleoprotein complex, they function on different molecular mechanism pathways to regulate different set of genes. Paupar maintains stem cell quiescence and restrict lineage progression from stem cells to TAPs by regulating the expression of key stem cell genes like Sox2, Hes1, and EGF as well as genes known for controlling neural growth and differentiation. To conclude, I discovered two interacting epigenetic regulators that control SVZ NSC and neurogenesis.

Advisor: Szele, F