An Rtn4/Nogo-A-interacting micropeptide modulates synaptic plasticity with age.

Micropeptides, encoded from small open reading frames of 300 nucleotides or less, are hidden throughout mammalian genomes, though few functional studies of micropeptides in the brain are published. Here, we describe a micropeptide known as the Plasticity-Associated Neural Transcript Short (Pants), located in the 22q11.2 region of the human genome, the microdeletion of which conveys a high risk for schizophrenia. Our data show that Pants is upregulated in early adulthood in the mossy fiber circuit of the hippocampus, where it exerts a powerful negative effect on long-term potentiation (LTP). Further, we find that Pants is secreted from neurons, where it associates with synapses but is rapidly degraded with stimulation. Pants dynamically interacts with Rtn4/Nogo-A, a well-studied regulator of adult plasticity. Pants interaction with Nogo-A augments its influence over postsynaptic AMPA receptor clustering, thus gating plasticity at adult synapses. This work shows that neural micropeptides can act as architectural modules that increase the functional diversity of the known proteome.

Haploinsufficiency of the 22q11.2 microdeletion gene Mrpl40 disrupts short-term synaptic plasticity and working memory through dysregulation of mitochondrial calcium.

Hemizygous deletion of a 1.5- to 3-megabase region on chromosome 22 causes 22q11.2 deletion syndrome (22q11DS), which constitutes one of the strongest genetic risks for schizophrenia. Mouse models of 22q11DS have abnormal short-term synaptic plasticity that contributes to working-memory deficiencies similar to those in schizophrenia. We screened mutant mice carrying hemizygous deletions of 22q11DS genes and identified haploinsufficiency of Mrpl40 (mitochondrial large ribosomal subunit protein 40) as a contributor to abnormal short-term potentiation (STP), a major form of short-term synaptic plasticity. Two-photon imaging of the genetically encoded fluorescent calcium indicator GCaMP6, expressed in presynaptic cytosol or mitochondria, showed that Mrpl40 haploinsufficiency deregulates STP via impaired calcium extrusion from the mitochondrial matrix through the mitochondrial permeability transition pore. This led to abnormally high cytosolic calcium transients in presynaptic terminals and deficient working memory but did not affect long-term spatial memory. Thus, we propose that mitochondrial calcium deregulation is a novel pathogenic mechanism of cognitive deficiencies in schizophrenia.

Insights into the catalytic mechanism of HlyC, the internal protein acyltransferase that activates Escherichia coli hemolysin toxin.

Hemolysin, a toxic protein secreted by pathogenic Escherichia coli, is converted from nontoxic prohemolysin, proHlyA, to toxic hemolysin, HlyA, by an internal protein acyltransferase, HlyC. Acyl-acyl carrier protein (ACP) is the essential acyl donor. The acyltransferase reaction proceeds through two partial reactions and entails formation of a reactive acyl-HlyC intermediate [Trent, M. S., Worsham, L. M., and Ernst-Fonberg, M. L. (1999) Biochemistry 38, 9541-9548]. The ping pong kinetic mechanism implied by these findings was validated using two different acyl-ACP substrates, thus verifying the independence of the previously demonstrated two partial reactions. Assessments of the stability of the acyl-HlyC intermediate revealed an increased stability at pH 8.6 compared to more acidic pHs. Mutations of a single conserved histidine residue essential for catalysis gave minimal activity when substituted with a tyrosine residue and no activity with a lysine residue. Unlike numerous other His23 mutants, however, the H23K enzyme showed significant acyl-HlyC formation although it was unable to transfer the acyl group from the proposed amide bond intermediate to proHlyA. These findings are compatible with transient formation of acyl-His23 during the course of HlyC catalysis. The effects of several other single site-directed mutations of conserved residues of HlyC on different portions of the reaction progress were examined using a 39 500 kDa fragment of proHlyA which was a more effective substrate than intact proHlyA.

Modification of the 50% maximum dose depth for 41-MeV (p+,Be) neutrons by use of filtration and/or transmission targets.

Several target configurations for the 41-MeV (p+,Be) reaction have been evaluated for the characteristics of the radiation field produced; depth dose, dose rate per microA, From analysis, it is concluded that to achieve the desired 13.2-cm depth for 50% of maximum dose and acceptable dose rate at a target-to-skin distance (TSD) of 125-150 cm, the neutron spectra must be filtered to preferentially absorb the lower-energy neutrons. Further increases in depth of 50% of maximum dose and a significant reduction in beryllium heating problems result if a partial transmission target is used with the terminal 30% of proton energy being deposited in a copper target backing.