Haploinsufficiency of X-linked intellectual disability gene CASK induces post-transcriptional changes in synaptic and cellular metabolic pathways.

Heterozygous mutations in the X-linked gene CASK are associated with intellectual disability, microcephaly, pontocerebellar hypoplasia, optic nerve hypoplasia and partially penetrant seizures in girls. The Cask+/- heterozygous knockout female mouse phenocopies the human disorder and exhibits postnatal microencephaly, cerebellar hypoplasia and optic nerve hypoplasia. It is not known if Cask+/- mice also display seizures, nor is known the molecular mechanism by which CASK haploinsufficiency produces the numerous documented phenotypes. 24-h video electroencephalography demonstrates that despite sporadic seizure activity, the overall electrographic patterns remain unaltered in Cask+/- mice. Additionally, seizure threshold to the commonly used kindling agent, pentylenetetrazol, remains unaltered in Cask+/- mice, indicating that even in mice the seizure phenotype is only partially penetrant and may have an indirect mechanism. RNA sequencing experiments on Cask+/- mouse brain uncovers a very limited number of changes, with most differences arising in the transcripts of extracellular matrix proteins and the transcripts of a group of nuclear proteins. In contrast to limited changes at the transcript level, quantitative whole-brain proteomics using iTRAQ quantitative mass-spectrometry reveals major changes in synaptic, metabolic/mitochondrial, cytoskeletal, and protein metabolic pathways. Unbiased protein-protein interaction mapping using affinity chromatography demonstrates that CASK may form complexes with proteins belonging to the same functional groups in which altered protein levels are observed. We discuss the mechanism of the observed changes in the context of known molecular function/s of CASK. Overall, our data indicate that the phenotypic spectrum of female Cask+/- mice includes sporadic seizures and thus closely parallels that of CASK haploinsufficient girls; the Cask+/- mouse is thus a face-validated model for CASK-related pathologies. We therefore surmise that CASK haploinsufficiency is likely to affect brain structure and function due to dysregulation of several cellular pathways including synaptic signaling and cellular metabolism.

Functionalization and peptide-based delivery of magnetic nanoparticles as an intracellular MRI contrast agent.

We report the development of functionalized superparamagnetic iron oxide nanoparticles with a PEG-modified, phospholipid micelle coating, and their delivery into living cells. The size of the coated particles, as determined by dynamic light scattering and electron microscopy, was found to be between 12 and 14 nm. The PEG-phospholipid coating resulted in high water solubility and stability, and the functional groups of modified PEG allowed for bioconjugation of various moieties, including a fluorescent dye and the Tat peptide. Efficient delivery of the functionalized nanoparticles into living cells was confirmed by fluorescence microscopy, relaxation time measurements, and magnetic resonance imaging (MRI). This demonstrates the feasibility of using functionalized magnetic nanoparticles with uniform (approximately 10 nm) sizes as an MRI contrast agent for intracellular molecular imaging in deep tissue. These micelle-coated iron oxide nanoparticles offer a versatile platform for conjugation of a variety of moieties, and their small size confers advantages for intracellular molecular imaging with minimal perturbation.