The Lineage Contribution and Role of Gbx2 in Spinal Cord Development

BACKGROUND: Forging a relationship between progenitors with dynamically changing gene expression and their terminal fate is instructive for understanding the logic of how cell-type diversity is established. The mouse spinal cord is an ideal system to study these mechanisms in the context of developmental genetics and nervous system development. Here we focus on the Gastrulation homeobox 2 (Gbx2) transcription factor, which has not been explored in spinal cord development. METHODOLOGY/PRINCIPAL FINDINGS: We determined the molecular identity of Gbx2-expressing spinal cord progenitors. We also utilized genetic inducible fate mapping to mark the Gbx2 lineage at different embryonic stages in vivo in mouse. Collectively, we uncover cell behaviors, cytoarchitectonic organization, and the terminal cell fate of the Gbx2 lineage. Notably, both ventral motor neurons and interneurons are derived from the Gbx2 lineage, but only during a short developmental period. Short-term fate mapping during mouse spinal cord development shows that Gbx2 expression is transient and is extinguished ventrally in a rostral to caudal gradient. Concomitantly, a permanent lineage restriction boundary ensures that spinal cord neurons derived from the Gbx2 lineage are confined to a dorsal compartment that is maintained in the adult and that this lineage generates inhibitory interneurons of the spinal cord. Using lineage tracing and molecular markers to follow Gbx2-mutant cells, we show that the loss of Gbx2 globally affects spinal cord patterning including the organization of interneuron progenitors. Finally, long-term lineage analysis reveals that the presence and timing of Gbx2 expression in interneuron progenitors results in the differential contribution to subtypes of terminally differentiated interneurons in the adult spinal cord. CONCLUSIONS/SIGNIFICANCE: We illustrate the complex cellular nature of Gbx2 expression and lineage contribution to the mouse spinal cord. In a broader context, this study provides a direct link between spinal cord progenitors undergoing dynamic changes in molecular identity and terminal neuronal fate

The Effects of Viscosity on the Linear Stability of Damped Stokes Waves, Downshifting, and Rogue Wave Generation

We investigate a higher order nonlinear Schrodinger equation with linear damping and weak viscosity, recently proposed as a model for deep water waves exhibiting frequency downshifting. Through analysis and numerical simulations, we discuss how the viscosity affects the linear stability of the Stokes wave solution, enhances rogue wave formation, and leads to permanent downshift in the spectral peak. In particular, we study the wave evolution over short-to-moderate time scales, when most rogue wave activity occurs, and explain the transition of the perturbed solution from the initial Benjamin-Feir instability to a predominantly oscillatory behavior. Finally, we determine the mechanism and timing of permanent downshift in the spectral peak and its relation to the location of the global minimum of the momentum and the magnitude of its second derivative

The Temporal Contribution of the Gbx2 Lineage to Cerebellar Neurons

The cerebellum (Cb) is an exquisite structure that controls elaborate motor behaviors and is essential for sensory-motor learning. During development, the Cb is derived from rhombomere 1 (r1). Within this embryonic compartment, precursors in r1 are patterned by signaling cues originating from the isthmus organizer (IsO) and subsequently undergo complex morphogenic movements to establish their final position in the mature Cb. The transcription factor Gbx2 is expressed in the developing Cb and is intimately involved in organizing and patterning the Cb. Nevertheless, how precursors expressing Gbx2 at specific embryonic time points contribute to distinct cell types in the adult Cb is unresolved. In this study, we used Genetic Inducible Fate Mapping (GIFM) to mark Gbx2-expressing precursors with fine temporal resolution and to subsequently track this lineage through embryogenesis. We then determined the terminal neuronal fate of the Gbx2 lineage in the adult Cb. Our analysis demonstrates that the Gbx2 lineage contributes to the Cb with marking over the course of five stages: Embryonic day 7.5 (E7.5) through E11.5. The Gbx2 lineage gives rise to Purkinje cells, granule neurons, and deep cerebellar neurons across these marking stages. Notably, the contribution of the Gbx2 lineage shifts as development proceeds with each marking stage producing a distinct profile of mature neurons in the adult Cb. These findings demonstrate the relationship between the temporal expression of Gbx2 and the terminal cell fate of neurons in the Cb. Based on these results, Gbx2 is critical to Cb development, not only for its well-defined role in positioning and maintaining the IsO, but also for guiding the development of Cb precursors and determining the identity of Cb neurons

Effects of cattle grazing and haying on wildlife conservation at National Wildlife Refuges in the United States

The National Wildlife Refuge System is perhaps the most important system of federal lands for protecting wildlife in the United States. Only at refuges has wildlife conservation been legislated to have higher priority than either recreational or commercial activities. Presently, private ranchers and farmers graze cattle on 981,954 ha and harvest hay on 12,021 ha at 123 National Wildlife Refuges. US Fish and Wildlife Service policy is to permit these uses primarily when needed to benefit refuge wildlife. To evaluate the success of this policy, I surveyed grassland management practices at the 123 refuges. The survey results indicate that in fiscal year 1980 there were 374,849 animal unit months (AUMs) of cattle grazing, or 41% more than was reported by the Fish and Wildlife Service. According to managers' opinions, 86 species of wildlife are positively affected and 82 are negatively affected by refuge cattle grazing or haying. However, quantitative field studies of the effect of cattle grazing and haying on wildlife coupled with the survey data on how refuge programs are implemented suggest that these activities are impeding the goal of wildlife conservation. Particular management problems uncovered by the survey include overgrazing of riparian habitats, wildlife mortality due to collisions with cattle fences, and mowing of migratory bird habitat during the breeding season. Managers reported that they spend $919,740 administering cattle grazing and haying; thus refuge grazing and haying programs are also expensive. At any single refuge these uses occupy up to 50% of refuge funds and 55% of staff time. In light of these results, prescribed burning may be a better wildlife management option than is either cattle grazing or haying.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48162/1/267_2005_Article_BF01867177.pd

The Second Creek War

Historians have traditionally viewed the “Creek War of 1836” as a minor police action centered on rounding up the Creek Indians for removal to Indian Territory. Using extensive archival research, John T. Ellisor demonstrates that, in fact, the Second Creek War was neither brief nor small. Indeed, armed conflict continued long after “peace” was declared and the majority of Creeks had been sent west. Ellisor’s study also broadly illuminates southern society just prior to the Indian removals, a time when many blacks, whites, and Natives lived in close proximity in the Old Southwest. In the Creek country, also called New Alabama, these ethnic groups began to develop a pluralistic society. When the 1830s cotton boom placed a premium on Creek land, however, dispossession of the Natives became an economic priority. Dispossessed and impoverished, some Creeks rose in armed revolt both to resist removal west and to drive the oppressors from their ancient homeland. Yet the resulting Second Creek War, which raged over three states, was fueled not only by Native determination but also by economic competition and was intensified not least by the massive government-sponsored land grab that constituted Indian removal. Because these circumstances also created fissures throughout southern society, both whites and blacks found it in their best interests to help the Creek insurgents. This first book-length examination of the Second Creek War shows how interethnic collusion and conflict characterized southern society during the 1830s

The Daily

Student newspaper of the University of Oklahoma in Norman, Oklahoma that includes national, local, and campus news along with advertising

The Daily

Student newspaper of the University of Oklahoma in Norman, Oklahoma that includes national, local, and campus news along with advertising