Role of cell cycle dynamics in early cell fate decisions of interneuron precursors in the MGE

• Applicant: Dr. Anna Katharina Schlusche
• Subject Area: Developmental Neurobiology ; Molecular Biology and Physiology of Neurons and Glial Cells
• Term: from 2018 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 417274402

Inhibitory interneurons are a small but crucial neuronal population, which show a great diversity in function, morphology and firing pattern. Indeed, diverse human pathologies like epilepsy, autism spectrum disorders or schizophrenia are associated with interneuron dysfunctions. Two major interneuron subpopulations, classified by the expression of Parvalbumin (PV) or Somatostatin (SST), originate from the transient structure of the medial ganglionic eminence (MGE). The cell fate decision to become a PV or SST interneuron is initiated early, in MGE mitotic progenitors whose specification may be influenced by regulators of cell divisions.In this project I aim to elucidate the molecular program underlying the PV vs. SST fate decision and probe how key regulators of the cell cycle and division mode act toward interneuron specification.I will use single cell RNA sequencing (scRNAseq) to investigate molecular programs directing MGE progenitor differentiation at embryonic (E) days E11.5, E13.5, and E15.5, assisted by mutant mouse lines. The conditional knockout in MGE of partition defective 3 (Pard3cKO) increases SST interneurons in the adult forebrain, while the cyclin D2 knockout (cD2KO) shows decreased PV interneuron densities. Pilot scRNAseq experiments at E13.5 show that different cell types could be robustly identified and classified into nine cell clusters in the wildtype (WT) MGE, representing radial glia cells (RGCs), intermediate progenitor cells (IPCs), and early neurons. In contrast to WT, the cD2KO mice lack an IPC cluster, supporting previous literature suggesting PV interneurons originate in the IPCs of the subventricular zone. In Pard3cKO MGE an RGC cluster is missing, suggesting that at E13.5, progenitors prematurely stop dividing to adopt an SST identity, consistent with data that SST neurons arise directly from RGCs. Data from E11.5 and E15.5 will test whether these genetic manipulations shift the timing of interneuron output from the MGE and will help identify key fate determinants.Previous studies in cortex established that asymmetric vs. symmetric divisions are key to regulation of neurogenesis and cell number output from embryonic germinal zones. However, little is known of how these division modes are connected to driving the cell cycle at the molecular level. PARD3 facilitates asymmetric divisions of RGCs, while cD2 expression mostly in IPCs suggests that it promotes symmetric divisions through an as yet unknown mechanism. In contrast to cD2, cD1 is only expressed in dividing RGCs, suggesting cD1 is important for asymmetric divisions. Exciting pilot data show PARD3 to physically interact with cD1 or cD2 with important differences. To probe the function of these biochemical differences, I will examine the impact of dual inactivation of PARD3 and cD2, compared to PARD3-cD1, on MGE cell cycle characteristics at different embryonic ages and determine the PV vs. SST cell fate decision outcomes in the adult forebrain.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professorin Margaret Elizabeth Ross, Ph.D.