Reach task-associated excitatory overdrive of motor cortical neurons following infusion with ALS-CSF

Converging evidence from transgenic animal models of amyotrophic lateral sclerosis (ALS) and human studies suggest alterations in excitability of the motor neurons in ALS. Specifically, in studies on human subjects with ALS the motor cortex was reported to be hyperexcitable. The present study was designed to test the hypothesis that infusion of cerebrospinal fluid from patients with sporadic ALS (ALS-CSF) into the rat brain ventricle can induce hyperexcitability and structural changes in the motor cortex leading to motor dysfunction. A robust model of sporadic ALS was developed experimentally by infusing ALS-CSF into the rat ventricle. The effects of ALS-CSF at the single neuron level were examined by recording extracellular single unit activity from the motor cortex while rats were performing a reach to grasp task. We observed an increase in the firing rate of the neurons of the motor cortex in rats infused with ALS-CSF compared to control groups. This was associated with impairment in a specific component of reach with alterations in the morphological characteristics of the motor cortex. It is likely that the increased cortical excitability observed in the present study could be the result of changes in the intrinsic properties of motor cortical neurons, a dysfunctional inhibitory mechanism and/or an underlying structural change culminating in a behavioral deficit.

Functions for rice RFL in vegetative axillary meristem specification and outgrowth

Roles for the transcription factor RFL in rice axillary meristem development were studied. Its regulatory effects on LAX1, CUC1, and OsPIN3 reveal its functions in axillary meristem specification and outgrowth.Axillary meristems (AMs) are secondary shoot meristems whose outgrowth determines plant architecture. In rice, AMs form tillers, and tillering mutants reveal an interplay between transcription factors and the phytohormones auxin and strigolactone as some factors that underpin this developmental process. Previous studies showed that knockdown of the transcription factor gene RFL reduced tillering and caused a very large decrease in panicle branching. Here, the relationship between RFL, AM initiation, and outgrowth was examined. We show that RFL promotes AM specification through its effects on LAX1 and CUC genes, as their expression was modulated on RFL knockdown, on induction of RFL:GR fusion protein, and by a repressive RFL-EAR fusion protein. Further, we report reduced expression of auxin transporter genes OsPIN1 and OsPIN3 in the culm of RFL knockdown transgenic plants. Additionally, subtle change in the spatial pattern of IR4 DR5:GFP auxin reporter was observed, which hints at compromised auxin transport on RFL knockdown. The relationship between RFL, strigolactone signalling, and bud outgrowth was studied by transcript analyses and by the tillering phenotype of transgenic plants knocked down for both RFL and D3. These data suggest indirect RFL-strigolactone links that may affect tillering. Further, we show expression modulation of the auxin transporter gene OsPIN3 upon RFL:GR protein induction and by the repressive RFL-EAR protein. These modified forms of RFL had only indirect effects on OsPIN1. Together, we have found that RFL regulates the LAX1 and CUC genes during AM specification, and positively influences the outgrowth of AMs though its effects on auxin transport.

Divergence in Patterns of Leaf Growth Polarity Is Associated with the Expression Divergence of miR396

Lateral appendages often show allometric growth with a specific growth polarity along the proximo-distal axis. Studies on leaf growth in model plants have identified a basipetal growth direction with the highest growth rate at the proximal end and progressively lower rates toward the distal end. Although the molecular mechanisms governing such a growth pattern have been studied recently, variation in leaf growth polarity and, therefore, its evolutionary origin remain unknown. By surveying 75 eudicot species, here we report that leaf growth polarity is divergent. Leaf growth in the proximo-distal axis is polar, with more growth arising from either the proximal or the distal end; dispersed with no apparent polarity; or bidirectional, with more growth contributed by the central region and less growth at either end. We further demonstrate that the expression gradient of the miR396-GROWTH-REGULATING FACTOR module strongly correlates with the polarity of leaf growth. Altering the endogenous pattern of miR396 expression in transgenic Arabidopsis thaliana leaves only partially modified the spatial pattern of cell expansion, suggesting that the diverse growth polarities might have evolved via concerted changes in multiple gene regulatory networks.