Project description:Our recently published M-CRIB atlas comprises 100 neonatal brain regions including 68 compatible with the widely-used Desikan-Killiany adult cortical atlas. A successor to the Desikan-Killiany atlas is the Desikan-Killiany-Tourville atlas, in which some regions with unclear boundaries were removed, and many existing boundaries were revised to conform to clearer landmarks in sulcal fundi. Our first aim here was to modify cortical M-CRIB regions to comply with the Desikan-Killiany-Tourville protocol, in order to offer: (a) compatibility with this adult cortical atlas, (b) greater labeling accuracy due to clearer landmarks, and (c) optimisation of cortical regions for integration with surface-based infant parcellation pipelines. Secondly, we aimed to update subcortical regions in order to offer greater compatibility with subcortical segmentations produced in FreeSurfer. Data utilized were the T2-weighted MRI scans in our M-CRIB atlas, for 10 healthy neonates (post-menstrual age at MRI 40-43 weeks, four female), and corresponding parcellated images. Edits were performed on the parcellated images in volume space using ITK-SNAP. Cortical updates included deletion of frontal and temporal poles and 'Banks STS,' and modification of boundaries of many other regions. Changes to subcortical regions included the addition of 'ventral diencephalon,' and deletion of 'subcortical matter' labels. A detailed updated parcellation protocol was produced. The resulting whole-brain M-CRIB 2.0 atlas comprises 94 regions altogether. This atlas provides comparability with adult Desikan-Killiany-Tourville-labeled cortical data and FreeSurfer-labeed subcortical data, and is more readily adaptable for incorporation into surface-based neonatal parcellation pipelines. As such, it offers the ability to help facilitate a broad range of investigations into brain structure and function both at the neonatal time point and developmentally across the lifespan.
Project description:Here, we report a novel mechanism of PDZ (PSD-95/Dlg/ZO-1) domain regulation that distorts a conserved element of PDZ ligand recognition. The polarity regulator Par-6 assembles a conserved multiprotein complex and is directly modulated by the Rho GTPase Cdc42. Cdc42 binds the adjacent Cdc42/Rac interactive binding (CRIB) and PDZ domains of Par-6, increasing C-terminal ligand binding affinity by 10-fold. By solving structures of the isolated PDZ domain and a disulfide-stabilized CRIB-PDZ, we detected a conformational switch that controls affinity by altering the configuration of the conserved "GLGF" loop. As a result, lysine 165 is displaced from the PDZ core by an adjacent hydrophobic residue, disrupting coordination of the PDZ ligand-binding cleft. Stabilization of the CRIB:PDZ interface restores K165 to its canonical location in the binding pocket. We conclude that a unique "dipeptide switch" in the Par-6 PDZ transmits a signal for allosteric activation to the ligand-binding pocket.
Project description:The Cdc42- and Rac-interactive binding motif (CRIB) of coronin binds to Rho GTPases with a preference for GDP-loaded Rac. Mutation of the Cdc42- and Rac-interactive binding motif abrogates Rac binding. This results in increased 1evels of activated Rac in coronin-deficient Dictyostelium cells (corA(-)), which impacts myosin II assembly. corA(-) cells show increased accumulation of myosin II in the cortex of growth-phase cells. Myosin II assembly is regulated by myosin heavy chain kinase-mediated phosphorylation of its tail. Kinase activity depends on the activation state of the p21-activated kinase a. The myosin II defect of corA(-) mutant is alleviated by dominant-negative p21-activated kinase a. It is rescued by wild-type coronin, whereas coronin carrying a mutated Cdc42- and Rac-interactive binding motif failed to rescue the myosin defect in corA(-) mutant cells. Ectopically expressed myosin heavy chain kinases affinity purified from corA(-) cells show reduced kinase activity. We propose that coronin through its affinity for GDP-Rac regulates the availability of GTP-Rac for activation of downstream effectors.