Focal adhesion kinase regulates the localization and retention of pro-B cells in bone marrow microenvironments.

Progenitor B cells reside in complex bone marrow (BM) microenvironments where they receive signals for growth and maturation. We reported previously that the CXCL12-focal adhesion kinase (FAK)-VLA4 pathway plays an important role in progenitor B cell adhesion and migration. In this study, we have conditionally targeted in B cells FAK, and found that the numbers of progenitor pro-B, pre-B, and immature B cells are reduced by 30-40% in B cell-specific FAK knockout mice. When cultured in methylcellulose with IL-7 ± CXCL12, Fak-deleted pro-B cells yield significantly fewer cells and colonies. Using in situ quantitative imaging cytometry, we establish that in longitudinal femoral BM sections, pro-B cells are preferentially localized in close proximity to the endosteum of the metaphyses and the diaphysis. Fak deletion disrupts the nonrandom distribution of pro-B cells and induces the mobilization of pro-B cells to the periphery in vivo. These effects of Fak deletion on pro-B cell mobilization and localization in BM are amplified under inflammatory stress, that is, after immunization with nitrophenol-conjugated chicken γ-globulin in alum. Collectively, these studies suggest the importance of FAK in regulating pro-B cell homeostasis and maintenance of their spatial distribution in BM niches.

Estimation of the acoustic range of bat echolocation for extended targets.

Extended natural structures of the bat environment such as trees, meadows, and water surfaces were ensonified in distances from 1 to 20 m and the echoes recorded using a mobile ultrasonic sonar system. By compensating the atmospheric attenuation, the attenuation of the reflected echo caused by diffraction, energy absorption of the target, and two-way-geometric spreading was calculated for each distance. For each target type the attenuation of the compensated echo sound pressure level was fitted over distance using a linear function which yields simple laws of reflection loss and geometric spreading. By adding to this function again variable atmospheric attenuation, the overall attenuation of a signal reflected from these targets can be estimated for various conditions. Given the dynamic range of a sonar system, the acoustic maximum detection distance can thus be estimated. The results show that the maximum range is dominantly limited by atmospheric attenuation. Energy loss in the reflecting surface is more variable than geometric spreading loss and accounts for most of the differences between the ensonified targets. Depending on atmospheric conditions, echolocation frequency, and the dynamic range of the sonar system, the maximum range for extended backgrounds such as a forest edge can be as short as 2.4 m.