PubMed · 9092262
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J Engel. 1996. Epilepsy: structural or functional?. https://pubmed.ncbi.nlm.nih.gov/9092262/
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DNA packaging into heterochromatin is a fundamental mechanism of transcriptional silencing, yet its role in regulating neural progenitor behavior during brain development remains poorly understood. Trimethylation of histone H3 lysine 9 (H3K9me3), catalyzed by the methyltransferases SETDB1, SUV39H1, and SUV39H2, is a defining feature of heterochromatin, but functional redundancy among these enzymes has obscured their developmental roles. Here, we generated a cortex-specific triple knockout mouse model lacking Setdb1, Suv39h1, and Suv39h2 to directly interrogate H3K9me3 function during corticogenesis. Combined loss of H3K9 methyltransferases caused genome-wide depletion of H3K9me3, disruption of neural progenitor cell-cycle progression, and impaired cortical neurogenesis, resulting in microcephaly. H3K9 methyltransferases preserve neural progenitor identity and function by silencing clustered protocadherins, meiosis-associated genes, and a cell-cycle restraint program through H3K9me3 deposition. Loss of H3K9me3 promoted local chromatin opening and increased transcription factor occupancy, enabling transposable elements to acquire cryptic enhancer activity and modulate proximal gene expression. Together, these findings establish H3K9me3 heterochromatin as an active regulator of neural progenitor dynamics and lineage fidelity, revealing a central epigenetic mechanism that restricts aberrant transcriptional programs to ensure cortical growth.
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Our aim was to determine the relative merits of short and long echo times (TE) with single-shot echo-planar imaging for imaging cerebral lesions such as multiple sclerosis. We examined seven patients with clinically definite multiple sclerosis were imaged at 1.5 T. Patients were scanned with spinecho, single-shot echo-planar imaging, using TEs of 45, 75, 105, and 135 ms. Region of interest (ROI) measurements were performed on 36 lesions at or above the level of the corona radiata. The mean image contrast (IC) was highest (231.1) for a TE of 45 ms, followed by 75 ms (218.9), 105 ms (217.9), and 135 ms (191.6). When mean contrast-to-noise ratios (C/N) were compared, the value was again highest (29.7) for TE 45 ms, followed by 75 ms (28.9), 105 ms (28.5), and 135 ms (26.3). In a lesion-by-lesion comparison, TE 45 ms had the highest IC and C/N in the largest number of cases (50 % and 47.2 %, respectively). IC and C/N for TE 45 ms were superior to those of 75 ms in 64% and 58%, respectively. These results support the use of relatively short TEs for single-shot echo-planar imaging in the setting of cerebral lesions such as multiple sclerosis.