The transcription and transport of messenger RNA (mRNA) are critical steps in regulating the spatial and temporal components of gene expression, but it has not been possible to observe the dynamics of endogenous mRNA in primary mammalian tissues. We have developed a transgenic mouse in which all β-actin mRNA is fluorescently labeled. We found that β-actin mRNA in primary fibroblasts localizes predominantly by diffusion and trapping as single mRNAs. In cultured neurons and acute brain slices, we found that multiple β-actin mRNAs can assemble together, travel by active transport, and disassemble upon depolarization by potassium chloride. Imaging of brain slices revealed immediate early induction of β-actin transcription after depolarization. Studying endogenous mRNA in live mouse tissues provides insight into its dynamic regulation within the context of the cellular and tissue microenvironment.

Acetic acid formation in Escherichia coli fermentation has been studied in continuous cultures. Experimental results suggest that the limited capacity of the oxidative metabolism (perhaps the limited capacity of TCA cycle) may be responsible for acetic acid formation. At low growth rates, both anabolic and catabolic requirements may be satisfied by the oxidative metabolism. However, at high growth rates these two demands may exceed the capacity of the oxidative metabolism alone. It is proposed that under these circumstances, E. coli reorganizes the oxidative metabolism to first meet the anabolic requisition and then supply the necessary amount of energy using both the remaining capacity of the oxidative metabolism and acetic acid formation metabolism. Escherichia coli selects acetic acid synthesis as the aerobic energy source because it generates the second largest amount of ATP and NADH(2). According to our proposition, acetic acid formation could be reduced by decreasing the anabolic requirement, i.e., reducing glucose uptake, or by increasing the capacity of the oxidative metabolism. These two approaches were experimentally confirmed by observing reduced acetic acid formation by reducing the glucose uptake with a yeast extract addition and enhancing the capacity of oxidative metabolism with a methionine addition.

Optical frequency domain imaging (OFDI) using swept laser sources is an emerging second-generation method for optical coherence tomography (OCT). Despite the widespread use of conventional OCT for retinal disease diagnostics, until now imaging the posterior eye segment with OFDI has not been possible. Here we report the development of a highperformance swept laser at 1050 nm and an ophthalmic OFDI system that offers an A-line rate of 18.8 kHz, sensitivity of >92 dB over a depth range of 2.4 mm with an optical exposure level of 550 μ W, and deep penetration into the choroid. Using these new technologies, we demonstrate comprehensive human retina, optic disc, and choroid imaging in vivo. This advance enables us to view choroidal vasculature in vivo without intravenous injection of fluorescent dyes and may provide a useful tool for evaluating choroidal as well as retinal diseases.