The Temporal Contribution of the Gbx2 Lineage to Cerebellar Neurons

Regulation of choroid plexus development and its functions

The choroid plexus (ChP) is an extensively vascularized tissue that protrudes into the brain ventricular system of all vertebrates. This highly specialized structure, consisting of the polarized epithelial sheet and underlying stroma, serves a spectrum of functions within the central nervous system (CNS), most notably the production of cerebrospinal fluid (CSF). The epithelial cells of the ChP have the competence to tightly modulate the biomolecule composition of CSF, which acts as a milieu functionally connecting ChP with other brain structures. This review aims to eloquently summarize the current knowledge about the development of ChP. We describe the mechanisms that control its early specification from roof plate followed by the formation of proliferative regions-cortical hem and rhombic lips-feeding later development of ChP. Next, we summarized the current knowledge on the maturation of ChP and mechanisms that control its morphological and cellular diversity. Furthermore, we attempted to review the currently available battery of molecular markers and mouse strains available for the research of ChP, and identified some technological shortcomings that must be overcome to accelerate the ChP research field. Overall, the central principle of this review is to highlight ChP as an intriguing and surprisingly poorly known structure that is vital for the development and function of the whole CNS. We believe that our summary will increase the interest in further studies of ChP that aim to describe the molecular and cellular principles guiding the development and function of this tissue.

Purkinje cells derived from TSC patients display hypoexcitability and synaptic deficits associated with reduced FMRP levels and reversed by rapamycin

Accumulating evidence suggests that cerebellar dysfunction early in life is associated with autism spectrum disorder (ASD), but the molecular mechanisms underlying the cerebellar deficits at the cellular level are unclear. Tuberous sclerosis complex (TSC) is a neurocutaneous disorder that often presents with ASD. Here, we developed a cerebellar Purkinje cell (PC) model of TSC with patient-derived human induced pluripotent stem cells (hiPSCs) to characterize the molecular mechanisms underlying cerebellar abnormalities in ASD and TSC. Our results show that hiPSC-derived PCs from patients with pathogenic TSC2 mutations displayed mTORC1 pathway hyperactivation, defects in neuronal differentiation and RNA regulation, hypoexcitability and reduced synaptic activity when compared with those derived from controls. Our gene expression analyses revealed downregulation of several components of fragile X mental retardation protein (FMRP) targets in TSC2-deficient hiPSC-PCs. We detected decreased expression of FMRP, glutamate receptor δ2 (GRID2), and pre- and post-synaptic markers such as synaptophysin and PSD95 in the TSC2-deficient hiPSC-PCs. The mTOR inhibitor rapamycin rescued the deficits in differentiation, synaptic dysfunction, and hypoexcitability of TSC2 mutant hiPSC-PCs in vitro. Our findings suggest that these gene expression changes and cellular abnormalities contribute to aberrant PC function during development in TSC affected individuals.

Temporal Expression of Wnt1 Defines the Competency State and Terminal Identity of Progenitors in the Developing Cochlear Nucleus and Inferior Colliculus

The auditory system contains a diverse array of interconnected anatomical structures that mediate the perception of sound. The cochlear nucleus of the hindbrain serves as the initial site of convergence for auditory stimuli, while the inferior colliculus of the midbrain serves as an integration and relay station for all ascending auditory information. We used Genetic Inducible Fate Mapping (GIFM) to determine how the timing of Wnt1 expression is related to the competency states of auditory neuron progenitors. We demonstrate that the Wnt1 lineage defines progenitor pools of auditory neurons in the developing midbrain and hindbrain. The timing of Wnt1 expression specifies unique cell types during embryogenesis and follows a mixed model encompassing a brief epoch of de novo expression followed by rapid and progressive lineage restriction to shape the inferior colliculus. In contrast, Wnt1 fate mapping of the embryonic hindbrain revealed de novo induction of Wnt1 in auditory hindbrain progenitors, which is related to the development of biochemically distinct neurons in the cochlear nucleus. Thus, we uncovered two modes of lineage allocation that explain the relationship between the timing of Wnt1 expression and the development of the cochlear nucleus and the inferior colliculus. Finally, our analysis of Wnt1^sw/sw mutant mice demonstrated a functional requirement of Wnt1 for the development of auditory midbrain and hindbrain neurons. Collectively, our study provides a deeper understanding of Wnt1 lineage allocation and function in mammalian brain development.