[Optogenetic activation of dorsal hippocampal astrocytic Rac1 blocks the learning of associative memory].

Rac1 belongs to the family of Rho GTPases, and plays important roles in the brain function. It affects the cell migration and axon guidance via regulating the cytoskeleton and cellular morphology. However, the effect of its dynamic activation in regulating physiological function remains unclear. Recently, a photoactivatable analogue of Rac1 (PA-Rac1) has been developed, allowing the activation of Rac1 by the specific wavelength of light in living cells. Thus, we constructed recombinant adeno-associated virus (AAV) of PA-Rac1 and its light-insensitive mutant PA-Rac1-C450A under the control of the mouse glial fibrillary acidic protein (mGFAP) promoter to manipulate Rac1 activity in astrocytes by optical stimulation. Primary culture of hippocampal astrocytes was infected with the recombinant AAV-PA-Rac1 or AAV-PA-Rac1-C450A. Real-time fluorescence imaging showed that the cell membrane of the astrocyte expressing PA-Rac1 protruded near the light spot, while the astrocyte expressing PA-Rac1-C450A did not. We injected AAV-PA-Rac1 and AAV-PA-Rac1-C450A into dorsal hippocampus to investigate the role of the activation of Rac1 in regulating the associative learning. With optical stimulation, the PA-Rac1 group, rather than the PA-Rac1-C450A group, showed slower learning curve during the fear conditioning compared with the control group, indicating that activating astrocytic Rac1 blocks the formation of contextual memory. Our data suggest that the activation of Rac1 in dorsal hippocampal astrocyte plays an important role in the associative learning.

Distribution of the Multidrug Resistance Gene cfr in Staphylococcus Isolates from Pigs, Workers, and the Environment of a Hog Market and a Slaughterhouse in Guangzhou, China.

Bacteria harboring cfr, a multidrug resistance gene, have high prevalence in livestock in China and might be transmitted to humans through direct contact or via contaminated food products. To better understand the epidemiology of cfr producers in the food chain, the prevalence and genetic analysis of Staphylococcus isolates recovered from pigs, workers, and meat-handling facilities (a slaughterhouse and a hog market in Guangzhou, China) were examined. Twenty (4.5%) cfr-positive Staphylococcus isolates (18 Staphylococcus simulans, 1 S. cohnii, and 1 S. aureus) were derived from pigs (16/312), the environment (2/52), and workers (2/80). SmaI pulsed-field gel electrophoresis of 26 staphylococcal strains (22 S. simulans and 4 S. cohnii), including previously reported cfr-carrying staphylococci of animal food origin, exhibited 19 major pulsed-field gel electrophoresis patterns (A-S). Clonal spread of cfr-carrying staphylococci among pigs, workers, and meat products was detected. The genetic contexts of cfr in plasmids (pHNKF3, pHNZT2, and pHNCR35) obtained from S. simulans of swine or human origin were similar to that of Staphylococcus species isolated from human clinics and animal-derived food. The cfr-carrying S. aureus strain isolated from floor swabs of the hog market was spa-type t889 and belonged to the ST9 clonal lineage. In summary, both clonal spread and horizontal transmission via mobile elements contributed to cfr dissemination among staphylococcal isolates obtained from different sources. To monitor potential outbreaks of cfr-positive bacteria, continued surveillance of this gene in animals at slaughter and in animal-derived food is warranted.