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Friday Science Review: September 9, 2011

Astrocytes Modulate Basal Synaptic Transmission

University of Montreal ♦ Montreal General Hospital ♦ Published in Cell, September 2, 2011

The astrocyte, a larger flattened cell type relative to the neuron, regulates the growth and survival of brain cells through the release of various growth factors and proteins. Recent findings indicate that they are also involved in regulating basal synaptic transmission. Although it has been known for some time that astrocytes are involved in modulating sustained synaptic transmission in the brain, researchers are in less agreement over whether or not astrocytes modulate basal synaptic transmission involving single synapses.  In this study, researchers found that astrocytes were activated by single action potentials and responded to this activation by releasing purines, specifically adenosine, which in turn increased basal transmission. It is believed that astrocyte activation occurs by way of the metabotropic glutamate subtype 5 receptors found on certain functional areas of the astrocyte process. After being release, purines bind to presynaptic A2a receptors on neurons, heightening basal synaptic transmission.

Neurogenesis Regulated by Alternative Splicing

University of Toronto ♦ Hospital for Sick Children ♦ King’s College London ♦ Published in Molecular Cell, September 2, 2011

Researchers have discovered a key mechanism that regulates the complex process of neurogenesis. Like many complex processes in the body, the process of neural development is controlled by a large array of genes and regulatory pathways. It appears that neurogenesis is activated by a protein known as nSR100, which alternatively splices another gene REST. Alternative splicing occurs when a gene is not transcribed by the cell’s protein machinery in its regular form. Instead, an alternative form, slightly different than the regular form (known as an isoform), is produced. This isoform can have reduced function or lose function entirely. In the case of REST, its alternative splice isoform REST4 still functions, however has vastly reduced activity. REST typically negatively regulates a panel of genes that promote neurogenesis, so in the presence of the isoform neurogenenesis increases. Experiments with mice confirm these findings; blocking nSR100 in the mouse brain impairs neurogenesis.

Maternal RNA Transcript Epigenetically Regulates Gene Expression

University of Toronto ♦ Published in Science, September 2, 2011

RNA can function in a number of ways above and beyond acting as a messenger between DNA and the translational machinery found in the cytoplasm. Researchers studying sex determination in C. elegans recently showed that expression of a wild-type allele controlling sex-determination, fem-1, can be regulated by a maternal fem-1 RNA transcript in the germ line. In C. elegans, the nematode worm frequently used as a model organism in studies of genetics, expression of the fem-1 gene is required for male development. In this study, females engineered to express deletions of the fem-1 gene at both alleles gave rise to offspring that exhibited a strong bias towards the female sex in their germ line. Researchers were able to rescue this defect in progeny by injecting a non-coding fem-1 RNA into the maternal germ line. Because the defect is heritable, scientists postulate that fem-1 is typically repressed epigenetically, and that a maternal fem-1 RNA transcript acts to block repression of the wild-type fem-1 gene allowing males to be produced under normal circumstances.

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