CC2D1A regulates human intellectual and social function as well as NF-κB signaling homeostasis.

Autism spectrum disorder (ASD) and intellectual disability (ID) are often comorbid, but the extent to which they share common genetic causes remains controversial. Here, we present two autosomal-recessive founder mutations in the CC2D1A gene causing fully penetrant cognitive phenotypes, including mild-to-severe ID, ASD, as well as seizures, suggesting shared developmental mechanisms. CC2D1A regulates multiple intracellular signaling pathways, and we found its strongest effect to be on the transcription factor nuclear factor κB (NF-κB). Cc2d1a gain and loss of function both increase activation of NF-κB, revealing a critical role of Cc2d1a in homeostatic control of intracellular signaling. Cc2d1a knockdown in neurons reduces dendritic complexity and increases NF-κB activity, and the effects of Cc2d1a depletion can be rescued by inhibiting NF-κB activity. Homeostatic regulation of neuronal signaling pathways provides a mechanism whereby common founder mutations could manifest diverse symptoms in different patients

Mutations in PYCR2, Encoding Pyrroline-5-Carboxylate Reductase 2, Cause Microcephaly and Hypomyelination

Despite recent advances in understanding the genetic bases of microcephaly, a large number of cases of microcephaly remain unexplained, suggesting that many microcephaly syndromes and associated genes have yet to be identified. Here, we report mutations in PYCR2, which encodes an enzyme in the proline biosynthesis pathway, as the cause of a unique syndrome characterized by postnatal microcephaly, hypomyelination, and reduced cerebral white-matter volume. Linkage mapping and whole-exome sequencing identified homozygous mutations (c.355C>T [p.Arg119Cys] and c.751C>T [p.Arg251Cys]) in PYCR2 in the affected individuals of two consanguineous families. A lymphoblastoid cell line from one affected individual showed a strong reduction in the amount of PYCR2. When mutant cDNAs were transfected into HEK293FT cells, both variant proteins retained normal mitochondrial localization but had lower amounts than the wild-type protein, suggesting that the variant proteins were less stable. A PYCR2-deficient HEK293FT cell line generated by genome editing with the clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 system showed that PYCR2 loss of function led to decreased mitochondrial membrane potential and increased susceptibility to apoptosis under oxidative stress. Morpholino-based knockdown of a zebrafish PYCR2 ortholog, pycr1b, recapitulated the human microcephaly phenotype, which was rescued by wild-type human PYCR2 mRNA, but not by mutant mRNAs, further supporting the pathogenicity of the identified variants. Hypomyelination and the absence of lax, wrinkly skin distinguishes this condition from that caused by previously reported mutations in the gene encoding PYCR2’s isozyme, PYCR1, suggesting a unique and indispensable role for PYCR2 in the human CNS during development

Microarray Noninvasive Neuronal Seizure Recordings from Intact Larval Zebrafish.

Zebrafish epilepsy models are emerging tools in experimental epilepsy. Zebrafish larvae, in particular, are advantageous because they can be easily genetically altered and used for developmental and drug studies since agents applied to the bath penetrate the organism easily. Methods for electrophysiological recordings in zebrafish are new and evolving. We present a novel multi-electrode array method to non-invasively record electrical activity from up to 61 locations of an intact larval zebrafish head. This method enables transcranial noninvasive recording of extracellular field potentials (which include multi-unit activity and EEG) to identify epileptic seizures. To record from the brains of zebrafish larvae, the dorsum of the head of an intact larva was secured onto a multi-electrode array. We recorded from individual electrodes for at least three hours and quantified neuronal firing frequency, spike patterns (continuous or bursting), and synchrony of neuronal firing. Following 15 mM potassium chloride- or pentylenetetrazole-infusion into the bath, spike and burst rate increased significantly. Additionally, synchrony of neuronal firing across channels, a hallmark of epileptic seizures, also increased. Notably, the fish survived the experiment. This non-invasive method complements present invasive zebrafish neurophysiological techniques: it affords the advantages of high spatial and temporal resolution, a capacity to measure multiregional activity and neuronal synchrony in seizures, and fish survival for future experiments, such as studies of epileptogenesis and development

Correction: Microarray Noninvasive Neuronal Seizure Recordings from Intact Larval Zebrafish.

[This corrects the article DOI: 10.1371/journal.pone.0156498.]

Confirmation of cell stability.

<p>Top panels in (<b>a)</b> show representative single cell recordings before and after KCl addition, top panels in (<b>b</b>) before and after PTZ addition. Bottom panels show averages of baseline and KCl recordings (<b>a</b>) and of baseline and PTZ recordings (<b>b</b>). Dashed lines indicate the width of the averaged action potential at half maximum of the amplitude and they approximate 1.3 ms in both recordings. Action potentials are stable over time as indicated by the unchanged shape of the traces.</p

Tools and steps for larva-mounting and timeline of recording.

<p><b>a:</b> Electrode chamber used for recordings (scale: 10 mm). <b>b:</b> Nylon mesh and slice anchor used to hold larva in place (scale: 5 mm). <b>c:</b> Placement of larva onto its dorsal side into the chamber with a drop of water (scale: 300 μm). <b>d:</b> Securing larva with nylon mesh (scale: 300 μm); microelectrode array is highlighted with red dots for enhanced visibility in this photo and the next. <b>e:</b> Larva positioned with head onto the microelectrode array (scale 300 μm). <b>f:</b> Timeline for experiments—each starting with a 15 min acclimation period, a 30 min control recording, and a 30 min recording time after drug application.</p

Addition of TTX to seizing larvae abolishes spiking.

<p>Spike rate plotted as a function of time (one channel shown). Recordings are made before and after PTZ addition. The addition of 0.4 mM TTX at 3900 s abolished firing. These experiments demonstrate a high likelihood that recorded signals arise from neurons firing action potentials (in contrast to myogenic potentials arising from tail-movements).</p

Spike rate as a function of time.

<p>Spike rate is plotted as a function of time (bin size: 1s)–one channel per condition is shown. No significant change in burst or firing rate follows a sham convulsant application (<b>a</b>). Epileptic activity is detected as increased action potential firing rate and bursting after the addition of 15 mM KCl (<b>b</b>) or 15 mM PTZ (<b>c</b>). Spike rate increases with drug addition.</p