PubMed · 14060671
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S H KRAINES. EMOTIONS: A PHYSIOLOGIC PROCESS.. https://doi.org/10.1016/s0033-3182(63)73167-7
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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.
Despite a decline in the overall rate of sudden infant death syndrome (SIDS), it remains the leading cause of postneonatal infant mortality. Research into underlying mechanisms of SIDS has still not yielded a morphological, histopathological correlate explaining aetiology and pathophysiology of an infant's sudden death. Of particular interest would be elucidating pathophysiological and molecular events immediately preceding the infant's sudden death. C-jun is an immediate early gene with a physiological role in orchestrating cellular responses following injury including a role in cell death. It is also one of the earliest and most consistent markers for neurons undergoing stress, degeneration and survival. We investigated the immunohistochemical expression of the acute phase protein c-jun within 47 separate cerebral regions of interest in the brains of 23 SIDS and 7 control cases for evidence of acute neuronal injury immediately preceding sudden death and to assess the distribution of cellular damage suggestive of pathophysiologically sensitive or critical cerebral regions. Dividing SIDS-cases and controls into subgroups with (1) no neuronal expression of c-jun at all or (2) some c-jun expression, a statistically significant higher c-jun expression for SIDS compared with control cases was established for the inferior colliculi ( P=0.008), the spinal trigeminal nuclei ( P=0.046) and the premotoric cortex layers II and IV ( P=0.029). The increased expression of c-jun in these areas might be directly related to the pathogenesis of sudden death, or may represent a secondary marker of neuronal injury with the primary event/injury being elsewhere in critical cardioventilatory circuits.
Action affordances can be activated by non-target objects in the visual field as well as by word labels attached to target objects. These activations have been manifested in interference effects of distractors and words on actions. We examined whether affordances could be activated implicitly by words representing graspable objects that were either large (e.g., APPLE) or small (e.g., GRAPE) relative to the target. Subjects first read a word and then grasped a wooden block. Interference effects of the words arose in the early portions of the grasping movements. Specifically, early in the movement, reading a word representing a large object led to a larger grip aperture than reading a word representing a small object. This difference diminished as the hand approached the target, suggesting on-line correction of the semantic effect. The semantic effect and its on-line correction are discussed in the context of ecological theories of visual perception, the distinction between movement planning and control, and the proximity of language and motor planning systems in the human brain.