Evolving features of human cortical development and the emerging roles of non-coding RNAs in neural progenitor cell diversity and function

Genetic Insights into Brain Morphology: a Genome-Wide Association Study of Cortical Thickness and T1-Weighted MRI Gray Matter-White Matter Intensity Contrast

In T1-weighted magnetic resonance imaging (MRI), cortical thickness (CT) and gray-white matter contrast (GWC) capture brain morphological traits and vary with age-related disease. To gain insight into genetic factors underlying brain structure and dynamics observed during neurodegeneration, this genome-wide association study (GWAS) quantifies the relationship between single nucleotide polymorphisms (SNPs) and both CT and GWC in UK Biobank participants (N = 43,002). To our knowledge, this is the first GWAS to investigate the genetic determinants of cortical T1-MRI GWC in humans. We found 251 SNPs associated with CT or GWC for at least 1% of cortical locations, including 42 for both CT and GWC; 127 for only CT; and 82 for only GWC. Identified SNPs include rs1080066 (THSB1, featuring the strongest association with both CT and GWC), rs13107325 (SLC39A8, linked to CT at the largest number of cortical locations), and rs864736 (KCNK2, associated with GWC at the largest number of cortical locations). Dimensionality reduction reveals three major gene ontologies constraining CT (neural signaling, ion transport, cell migration) and four constraining GWC (neural cell development, cellular homeostasis, tissue repair, ion transport). Our findings provide insight into genetic determinants of GWC and CT, highlighting pathways associated with brain anatomy and dynamics of neurodegeneration. These insights can assist the development of gene therapies and treatments targeting brain diseases.

Evaluation of histological and ultrastructural changes provoked by prenatal tramadol on postnatal cortical cerebellar neuronal development in rats: possible implication of Ki67, GFAP and MicroRNA-7/P53 signalling trajectories

Tramadol is a novel centrally acting analgesic. Despite, its implementation during pregnancy may impair neuronal survival and synaptic development in neonatal cerebella. The current investigation assessed the histological and ultrastructural alterations in postnatal cortical cerebellar neuronal development induced by prenatal tramadol. 30 offsprings were divided to control group I: fifteen pups born to mothers given saline from D10 till D21 of gestation. Tramadol-treated group II: fifteen pups born to mothers received tramadol HCL (50 mg/kg/day) from D10 till D21 of gestation. Pups were categorized into three subgroups (a, b, and c) and offered for sacrifice on the seventh, fourteenth and twenty-first post-natal days. Light microscopic examination revealed the overcrowding and signs of red degeneration affecting purkinje cell layer. Neurodegenerative signs of both purkinje and granule cell neurons were also confirmed by TEM in form of chromatin condensation, dilated Golgi channels, disrupted endoplasmic reticulum, marked infolding of the nuclear envelope and decrease in granule cell precursors. In addition, the astrocytic processes and terminal nerve axons appeared with different degrees of demyelination and decreased number of oligodendrocytes and degenerated mitochondria. Furthermore, group II exhibited an increase in P53 immune expression. The area percentage of apoptotic cells detected by TUNEL assay was significantly increased. Besides to the significant decrease of Ki67 immunoreactivity in the stem neuronal cell progenitors. Quantitative PCR results showed a significant decline in micro RNA7 gene expression in tramadol treated groups resulting in affection of multiple target genes in P53 signaling pathways, improper cortical size and defect in neuronal development.

miR-409-3p represses Cited2 to refine neocortical layer V projection neuron identity

The evolutionary emergence of the corticospinal tract and corpus callosum are thought to underpin the expansion of complex motor and cognitive abilities in mammals. Molecular mechanisms regulating development of the neurons whose axons comprise these tracts, the corticospinal and callosal projection neurons, remain incompletely understood. Our previous work identified a genomic cluster of microRNAs (miRNAs), Mirg/12qF1, that is unique to placental mammals and specifically expressed by corticospinal neurons, and excluded from callosal projection neurons, during development. We found that one of these, miR-409-3p, can convert layer V callosal into corticospinal projection neurons, acting in part through repression of the transcriptional regulator Lmo4. Here we show that miR-409-3p also directly represses the transcriptional co-regulator Cited2, which is highly expressed by callosal projection neurons from the earliest stages of neurogenesis. Cited2 is highly expressed by intermediate progenitor cells (IPCs) in the embryonic neocortex while Mirg, which encodes miR-409-3p, is excluded from these progenitors. miR-409-3p gain-of-function (GOF) in IPCs results in a phenocopy of established Cited2 loss-of-function (LOF). At later developmental stages, both miR-409-3p GOF and Cited2 LOF promote the expression of corticospinal at the expense of callosal projection neuron markers in layer V. Taken together, this work identifies previously undescribed roles for miR-409-3p in controlling IPC numbers and for Cited2 in controlling callosal fate. Thus, miR-409-3p, possibly in cooperation with other Mirg/12qF1 miRNAs, represses Cited2 as part of the multifaceted regulation of the refinement of neuronal cell fate within layer V, combining molecular regulation at multiple levels in both progenitors and post-mitotic neurons.