Tracing the origins of fate and diversity of projection neurons in the mouse neocortex

• Autores: Irene Varela Martínez
• Directores de la Tesis: Marta Nieto López (dir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2025
• Idioma: inglés
• Número de páginas: 142
• Títulos paralelos:
  • Trazando los orígenes del destino y la diversidad de las neuronas de proyección en el neocórtex del ratón
• Tribunal Calificador de la Tesis: Víctor Borrell Franco (presid.), Marta Pérez Pereira (secret.), Sara Bizzotto (voc.)
• Programa de doctorado: Programa de Doctorado en Biociencias Moleculares por la Universidad Autónoma de Madrid
• Materias:
  • Ciencias de la vida
    • Biología animal (zoología)
      • Mamíferos
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • The neocortex, a hallmark of mammalian brains, is renowned as the seat of higher-order brain functions. During development, diverse subtypes of excitatory projection neurons (PNs) are organized into a characteristic six-layered cytoarchitecture. Radial glia progenitors (RGPs) in the dorsal telencephalon produce the full spectrum of PN subtypes, following a highly organized program of proliferation and differentiation. Yet, the diversity of cell lineages derived from RGPs and their specific contribution to PN subtype diversity remain uncertain.

    A central challenge in investigating cell lineage diversity is the difficulty in PN classification. In the adult neocortex, the intricate axonal patterns of mature PNs hinder their identification through straightforward axonal tracing techniques. However, prior to axonal refinement, young differentiating PNs share axonal projections into cardinal routes, offering a solution to the classification problem. By mapping the developmental axonal projections of immature PNs we identified the corpus callosum (CC) as a cardinal axonal route specific for intra-telencephalic (IT) PNs, not only in the upper layers (ULs) but also in the deep layers (DLs). Furthermore, we demonstrated that the injection of fluorescent tracers into the CC at early stages provides a precise strategy to differentiate IT-PNs from extra-telencephalic (ET) PNs, the two main PN subtypes in the neocortex. This distinction is specifically relevant in the DLs, where both PN subtypes are tightly intermingled. Notably, we found that the ipsilateral intra-hemispheric patterning of IT-PN projections is set out early in development, contrary to inter-hemispheric callosal routes.

    We next investigated the birthdates of ET-PNs and IT-PNs. Our data revealed an ET-PN first, IT-PN-last order of neurogenesis, since the production of DL and UL IT-PNs overlaps during late neurogenesis. To elucidate how individual RGPs produce the two PN subtypes, we combined Mosaic Analysis with Double Markers (MADM)-based clonal analysis with early callosal axonal tracing. Our experiments revealed that the early emergence of IT-PN fate-restricted RGPs during lineage progression constitutes a hierarchical decision that defines a lineage branch between IT-PNs and ET-PNs. From the onset of neurogenesis, an increasing fraction of RGPs commit to producing IT-PNs across the DLs and ULs. The frequency of this event increases with the progression of neurogenesis, explaining the temporal offset in the birthdates of ET-PNs and IT-PNs. Finally, we investigated the role of POU-domain class 3 (POU3F) family of transcription factors (TFs) in producing IT-PN outputs, postulating POU3F2 as a fate determinant of IT-PN identity.

    Our work introduces conceptual advances and novel perspectives on the understanding of the principles governing RGP lineage progression and PN specification in the mammalian neocortex. These findings not only enhance our understanding of brain development but also shed light on critical aspects essential for elucidating the mechanisms underlying brain evolution and neurodevelopmental disorders.