Browsing UA Faculty Research by Subjects
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Invasive buffel grass (Cenchrus ciliaris) increases water stress and reduces success of native perennial seedlings in southeastern ArizonaAlthough buffel grass (Cenchrus ciliaris) invasions on several continents have significant ecological impacts, little information is available on its stage-specific interactions with native vegetation. In areas of North America’s Sonoran Desert highly impacted by buffel grass, perennial plants are particularly vulnerable during the recruitment stage. We studied the impact of buffel grass on the emergence and early survival of native perennials that germinate during monsoon season with a field experiment. We used a pot experiment to test whether proximity to buffel grass induced water stress in the seedlings of a locally dominant native tree, the foothills palo verde (Parkinsonia microphylla). Seedlings of native perennials emerged at nearly twice the rate, and survived longer, on field plots where mature buffel grass was removed, or had never invaded, than where buffel grass remained. The stable isotope signatures of carbon in palo verde seedlings grown in pots with buffel grass indicated higher stomatal closure consistent with greater water stress than in seedlings grown alone. A stage-structured model based on palo verde population dynamics illustrates that if only recruitment rates were affected by buffel grass, palo verde would likely remain on the landscape, though at reduced densities. However, the long-lived nature of perennials implies we have yet to observe the full impacts of the invasion. The model indicates the kinds of studies needed to fully predict the impact of buffel grass.
The small GTPase RhoG mediates glioblastoma cell invasionBACKGROUND:The invasion of glioblastoma cells into regions of the normal brain is a critical factor that limits current therapies for malignant astrocytomas. Previous work has identified roles for the Rho family guanine nucleotide exchange factors Trio and Vav3 in glioblastoma invasion. Both Trio and Vav3 act on the small GTPase RhoG. We therefore examined the role of RhoG in the invasive behavior of glioblastoma cells.RESULTS:We found that siRNA-mediated depletion of RhoG strongly inhibits invasion of glioblastoma cells through brain slices ex vivo. In addition, depletion of RhoG has a marginal effect on glioblastoma cell proliferation, but significantly inhibits glioblastoma cell survival in colony formation assays. We also observed that RhoG is activated by both HGF and EGF, two factors that are thought to be clinically relevant drivers of glioblastoma invasive behavior, and that RhoG is overexpressed in human glioblastoma tumors versus non-neoplastic brain. In search of a mechanism for the contribution of RhoG to the malignant behavior of glioblastoma cells, we found that depletion of RhoG strongly inhibits activation of the Rac1 GTPase by both HGF and EGF. In line with this observation, we also show that RhoG contributes to the formation of lamellipodia and invadopodia, two functions that have been shown to be Rac1-dependent.CONCLUSIONS:Our functional analysis of RhoG in the context of glioblastoma revealed a critical role for RhoG in tumor cell invasion and survival. These results suggest that targeting RhoG-mediated signaling presents a novel avenue for glioblastoma therapy.