<i>APOE</i> and Cerebral Small Vessel Disease Markers in Patients With Intracerebral Hemorrhage
Isabel C. Hostettler, David Seiffge, Andrew Wong, Gareth Ambler, Duncan Wilson, Clare Shakeshaft, Gargi Banerjee, Nikhil Sharma, Hans Rolf Jäger, Hannah Cohen, Tarek Yousry, Rustam Al‐Shahi Salman, Gregory Y.H. Lip, Martin M. Brown, Keith W. Muir, Henry Houlden, David J. Werring
Abstract
Homeostatic regulation of ionic currents is of paramount importance during periods of synaptic growth or remodeling. Our previous work has identified the translational repressor Pumilio (Pum) as a regulator of sodium current (<i>I</i><sub>Na</sub>) and excitability in <i>Drosophila</i> motoneurons. In this current study, we show that Pum is able to bind directly the mRNA encoding the <i>Drosophila</i> voltage-gated sodium channel <i>paralytic</i> (<i>para</i>). We identify a putative binding site for Pum in the 3′ end of the <i>para</i> open reading frame (ORF). Characterization of the mechanism of action of Pum, using whole-cell patch clamp and real-time reverse transcription-PCR, reveals that the full-length protein is required for translational repression of <i>para</i> mRNA. Additionally, the cofactor Nanos is essential for Pum-dependent <i>para</i> repression, whereas the requirement for Brain Tumor (Brat) is cell type specific. Thus, Pum-dependent regulation of <i>I</i><sub>Na</sub> in motoneurons requires both Nanos and Brat, whereas regulation in other neuronal types seemingly requires only Nanos but not Brat. We also show that Pum is able to reduce the level of <i>nanos</i> mRNA and as such identify a potential negative-feedback mechanism to protect neurons from overactivity of Pum. Finally, we show coupling between <i>I</i><sub>Na</sub> (<i>para</i>) and <i>I</i><sub>K</sub> (<i>Shal</i>) such that Pum-mediated change in <i>para</i> results in a compensatory change in <i>Shal</i>. The identification of <i>para</i> as a direct target of Pum represents the first ion channel to be translationally regulated by this repressor and the location of the binding motif is the first example in an ORF rather than in the canonical 3′-untranslated region of target transcripts.