Summary We report an unexpected role for protease signaling in neural tube closure and formation of the central nervous system. Mouse embryos lacking protease-activated receptor 1 and 2 showed defective hindbrain and posterior neuropore closure and developed exencephaly and spina bifida, important human congenital anomalies. Par1 and Par2 were expressed in surface ectoderm, Par2 selectively along the line of closure. Ablation of Gi/z and Rac1 function in these Par2-expressing cells disrupted neural tube closure, further implicating G protein-coupled receptors and identifying a likely effector pathway. Cluster analysis of protease and Par2 expression patterns revealed a group of membrane-tethered proteases often co-expressed with Par2. Among these, matriptase activated Par2 with picomolar potency, and hepsin and prostasin activated matriptase. Together, our results suggest a role for protease-activated receptor signaling in neural tube closure and identify a local protease network that may trigger Par2 signaling and monitor and regulate epithelial integrity in this context.

The formation and stabilization of the aragonite polymorph in the nacre layer of mollusks is an intriguing process, yet very little is known with regard to the participation of proteins in this process. Previously, we identified the 30 AA N-terminal mineral binding domains (AP7-N, AP24-N, n16-N) of three different nacre-specific proteins (AP7, AP24, n16). These three domains differ in primary sequence and induce morphological changes in CaCO3 crystals in vitro. Using AFM microscopy, we investigated the adsorption of AP7-N, AP24-N, and n16-N onto calcite dislocation hillocks. We observe that both AP7-N and AP24-N are multifunctional; they not only inhibit obtuse step advance but also induce rounded, amorphous-appearing deposits on hillock terraces. In contrast, n16-N pins corner sites at the junction of acute and obtuse steps and promote the emergence of a new set of steps approximately oriented along a line joining the obtuse−obtuse and the acute−acute corners. Random scrambling of the n16-N and AP7-N sequences resulted in substantially reduced mineral modification activities, indicating that the primary sequence of both polypeptides is crucial for correct recognition of surface features. These findings indicate that nacre proteins evolved specialized mineral interaction domains that either recognize different surface features (AP7-N, AP24-N versus n16-N), or recognize the same features, but with different binding and catalytic activities (AP24-N versus AP7-N). These functional differences may arise from the differences in primary and secondary structure specific to each N-terminal domain. Hypothetically, this molecular diversity would allow complementary and simultaneous protein control (“molecular tuning”) of different features of the crystal growth process.

The critical length and density of the steps, rather than step morphology and velocity of deposition, are useful for understanding the effectiveness of the additive molecules in modifying the crystallization kinetics in biomineralization. This biological control stems from a change in solid–solution interfacial energies, which delays the formation of active steps on the growing crystal face (see picture).

We report cadmium-free, biocompatible (Zn)CuInS2 quantum dots with long fluorescence lifetimes as superior bioimaging probes using time-gated detection to suppress cell autofluorescence and improve the signal:background ratio by an order of magnitude. These results will be important for developing non-toxic fluorescence imaging probes for ultrasensitive biomedical diagnostics.