The role of sensory organs and the forebrain for the development of the craniofacial shape as revealed by Foxg1-cre-mediated microRNA loss

Cranial development is critically influenced by the relative growth of distinct elements. Previous studies have shown that the transcription factor Foxg1 is essential the for development of the telencephalon, olfactory epithelium, parts of the eye and the ear. Here we investigate the effects of a Foxg1-cre-mediated conditional deletion of Dicer1 and microRNA (miRNA) depletion on mouse embryos. We report the rapid and complete loss of the telencephalon and cerebellum as well as the severe reduction in the ears and loss of the anterior half of the eyes. These losses result in unexpectedly limited malformations of anterodorsal aspects of the skull. We investigated the progressive disappearance of these initially developing structures and found a specific miRNA of nervous tissue, miR-124, to disappear before reduction in growth of the specific neurosensory areas. Correlated with the absence of miR-124, these areas showed numerous apoptotic cells that stained positive for anticleaved caspase 3 and the phosphatidylserine stain PSVue® before the near or complete loss of those brain and sensory areas (forebrain, cerebellum, anterior retina, and ear). We conclude that Foxg1-cre-mediated conditional deletion of Dicer1 leads to the absence of functional miRNA followed by complete or nearly complete loss of neurons. Embryonic neurosensory development therefore depends critically on miRNA. Our data further suggest that loss of a given neuronal compartment can be triggered using early deletion of Dicer1 and thus provides a novel means to genetically remove specific neurosensory areas to investigate loss of their function on morphology (this study) or signal processing within the brain.

Cortical development in the fetus and the newborn: advanced MR techniques

Brain function is tightly linked to the development of the cortex. Until recently, assessing the human cortical development and folding was not possible in vivo. It is magnetic resonance imaging and new post-processing image analysis tools that have improved the understanding of cortical development. The combination of conventional magnetic resonance imaging and diffusion tensor imaging has further allowed depiction of the relationship of changes in intracortical layering and cortical folding. Being able to follow these early developmental processes has elucidated changes in early brain development due to changed environmental conditions in fetal life such as twinning and fetal growth restriction and postnatal conditions such as prematurity. This review further illustrates new data on brain structural asymmetries linked to the emergence of early language functions.