Integrated Calendar

Most excitatory cells in layer 4 of the mouse somatosensory cortex are spiny stellate (SpSt) neurons, which receive nearly all their excitatory input from the thalamus and from other SpSt neurons in the same barrel. Because layer 4 is the key entrance point into the cortical circuit, we assume that SpSt neurons respond rapidly to sensory input. However, these cells are very small, and there are strong theoretical reasons to suspect that their compact morphology could impair their capacity to encode high input frequencies and thus hamper the temporal fidelity of cortical processing. We use whole-cell patch clamp to measure the temporal properties of asynchronous noise in SpSt cells as compared with the much larger layer 5 pyramidal (Pyr) cells, and characterize the capabilities of both cell types to encode high frequencies in a synaptically active-like environment. We find that individual SpSt cells indeed have a much narrower dynamic range than Pyr cells when probed with inputs on a background of identical noise characteristics. However, the synaptic dynamics in SpSt cells, as evidenced by the correlation time of asynchronous noise, is slower than in Pyr neurons, and the slower correlation time of the SpSt cells is associated with significant broadening of their dynamic range. We further show that this compensatory improvement in encoding bandwidth of sensory input depends on activation of potassium conductances, as it decreases when potassium channels are pharmacologically blocked.

Alkene ozonolysis is a primary oxidation pathway for alkenes emitted into the troposphere and also an important source of atmospheric hydroxyl radicals. Alkene ozonolysis takes place on a reaction path with multiple minima and barriers along the way to OH products. In particular, a key reaction intermediate, known as the Criegee intermediate, R1R2COO, had eluded detection until very recently. In this laboratory, the simplest Criegee intermediate, CH2OO, and methyl-substituted Criegee intermediates, CH3CHOO and (CH3)2COO, have now been generated by an alternative synthetic route, detected by VUV photoionization, and characterized on a strong * transition. Most recently, our studies have focused on vibrational activation of methyl-substituted Criegee intermediates in the vicinity of the barrier for 1,4 hydrogen transfer that leads to OH products. The experiments reveal infrared transitions in the CH stretch overtone region that initiate unimolecular decay as well as the rate of the appearance of OH products through direct time-domain measurements. Comparison with high level theory shows that tunneling through the barrier makes a significant contribution to the decay rate. The dissociation dynamics are also examined through the translational and internal energy distributions of the OH products, which reflect critical configurations along the reaction pathway from the barrier for hydrogen transfer to OH products. Finally, the results will be extended to thermally averaged unimolecular decay of stabilized Criegee intermediates under atmospheric conditions.

Alternative promoter usage contributes to the complexity of genome-encoded transcripts but little is known about its impact on translation. To obtain a global view of transcription start site (TSS) selection effect on translation we performed TSS mapping of the translatome under normal growth condition and following energy stress. Our findings uncovered several levels of coordination of transcription and translation. In this talk I will present the data analysis of these experiments along with in-depth inquiries of several intriguing examples.