Developmental Functions of miR156-Regulated \u3cem\u3eSQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL)\u3c/em\u3e Genes in \u3cem\u3eArabidopsis thaliana\u3c/em\u3e

Correct developmental timing is essential for plant fitness and reproductive success. Two important transitions in shoot development—the juvenile-to-adult vegetative transition and the vegetative-to-reproductive transition—are mediated by a group of genes targeted by miR156, SQUAMOSA PROMOTER BINDING PROTEIN (SBP) genes. To determine the developmental functions of these genes in Arabidopsis thaliana, we characterized their expression patterns, and their gain-of-function and loss-of-function phenotypes. Our results reveal that SBP-LIKE (SPL) genes in Arabidopsis can be divided into three functionally distinct groups: 1) SPL2, SPL9, SPL10, SPL11, SPL13 and SPL15 contribute to both the juvenile-to-adult vegetative transition and the vegetative-to-reproductive transition, with SPL9, SP13 and SPL15 being more important for these processes than SPL2, SPL10 and SPL11; 2) SPL3, SPL4 and SPL5 do not play a major role in vegetative phase change or floral induction, but promote the floral meristem identity transition; 3) SPL6 does not have a major function in shoot morphogenesis, but may be important for certain physiological processes. We also found that miR156-regulated SPL genes repress adventitious root development, providing an explanation for the observation that the capacity for adventitious root production declines as the shoot ages. miR156 is expressed at very high levels in young seedlings, and declines in abundance as the shoot develops. It completely blocks the expression of its SPL targets in the first two leaves of the rosette, and represses these genes to different degrees at later stages of development, primarily by promoting their translational repression. These results provide a framework for future studies of this multifunctional family of transcription factors, and offer new insights into the role of miR156 in Arabidopsis development

The impact of surgical delay on resectability of colorectal cancer: An international prospective cohort study

AIM: The SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery. METHODS: This was an international prospective cohort study of consecutive colorectal cancer patients with a decision for curative surgery (January-April 2020). Surgical delay was defined as an operation taking place more than 4 weeks after treatment decision, in a patient who did not receive neoadjuvant therapy. A subgroup analysis explored the effects of delay in elective patients only. The impact of longer delays was explored in a sensitivity analysis. The primary outcome was complete resection, defined as curative resection with an R0 margin. RESULTS: Overall, 5453 patients from 304 hospitals in 47 countries were included, of whom 6.6% (358/5453) did not receive their planned operation. Of the 4304 operated patients without neoadjuvant therapy, 40.5% (1744/4304) were delayed beyond 4 weeks. Delayed patients were more likely to be older, men, more comorbid, have higher body mass index and have rectal cancer and early stage disease. Delayed patients had higher unadjusted rates of complete resection (93.7% vs. 91.9%, P = 0.032) and lower rates of emergency surgery (4.5% vs. 22.5%, P < 0.001). After adjustment, delay was not associated with a lower rate of complete resection (OR 1.18, 95% CI 0.90-1.55, P = 0.224), which was consistent in elective patients only (OR 0.94, 95% CI 0.69-1.27, P = 0.672). Longer delays were not associated with poorer outcomes. CONCLUSION: One in 15 colorectal cancer patients did not receive their planned operation during the first wave of COVID-19. Surgical delay did not appear to compromise resectability, raising the hypothesis that any reduction in long-term survival attributable to delays is likely to be due to micro-metastatic disease

Mechanisms of HDA6-mediated rRNA gene silencing: suppression of intergenic Pol II transcription and differential effects on maintenance versus siRNA-directed cytosine methylation

The Arabidopsis histone deacetylase HDA6 is required to silence transgenes, transposons, and ribosomal RNA (rRNA) genes subjected to nucleolar dominance in genetic hybrids. In nonhybrid Arabidopsis thaliana, we show that a class of 45S rRNA gene variants that is normally inactivated during development fails to be silenced in hda6 mutants. In these mutants, symmetric cytosine methylation at CG and CHG motifs is reduced, and spurious RNA polymerase II (Pol II) transcription occurs throughout the intergenic spacers. The resulting sense and antisense spacer transcripts facilitate a massive overproduction of siRNAs that, in turn, direct de novo cytosine methylation of corresponding gene sequences. However, the resulting de novo DNA methylation fails to suppress Pol I or Pol II transcription in the absence of HDA6 activity; instead, euchromatic histone modifications typical of active genes accumulate. Collectively, the data reveal a futile cycle of unregulated transcription, siRNA production, and siRNA-directed DNA methylation in the absence of HDA6-mediated histone deacetylation. We propose that spurious Pol II transcription throughout the intergenic spacers in hda6 mutants, combined with losses of histone deacetylase activity and/or maintenance DNA methylation, eliminates repressive chromatin modifications needed for developmental rRNA gene dosage control

Developmental Functions of miR156-Regulated <i>SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL)</i> Genes in <i>Arabidopsis thaliana</i>

<div><p>Correct developmental timing is essential for plant fitness and reproductive success. Two important transitions in shoot development—the juvenile-to-adult vegetative transition and the vegetative-to-reproductive transition—are mediated by a group of genes targeted by miR156, SQUAMOSA PROMOTER BINDING PROTEIN (SBP) genes. To determine the developmental functions of these genes in <i>Arabidopsis thaliana</i>, we characterized their expression patterns, and their gain-of-function and loss-of-function phenotypes. Our results reveal that <i>SBP-LIKE</i> (<i>SPL</i>) genes in <i>Arabidopsis</i> can be divided into three functionally distinct groups: 1) <i>SPL2</i>, <i>SPL9</i>, <i>SPL10</i>, <i>SPL11</i>, <i>SPL13</i> and <i>SPL15</i> contribute to both the juvenile-to-adult vegetative transition and the vegetative-to-reproductive transition, with <i>SPL9</i>, <i>SP13</i> and <i>SPL15</i> being more important for these processes than <i>SPL2</i>, <i>SPL10</i> and <i>SPL11</i>; 2) <i>SPL3</i>, <i>SPL4</i> and <i>SPL5</i> do not play a major role in vegetative phase change or floral induction, but promote the floral meristem identity transition; 3) <i>SPL6</i> does not have a major function in shoot morphogenesis, but may be important for certain physiological processes. We also found that miR156-regulated <i>SPL</i> genes repress adventitious root development, providing an explanation for the observation that the capacity for adventitious root production declines as the shoot ages. miR156 is expressed at very high levels in young seedlings, and declines in abundance as the shoot develops. It completely blocks the expression of its <i>SPL</i> targets in the first two leaves of the rosette, and represses these genes to different degrees at later stages of development, primarily by promoting their translational repression. These results provide a framework for future studies of this multifunctional family of transcription factors, and offer new insights into the role of miR156 in <i>Arabidopsis</i> development.</p></div

Lower-limb robotic devices: controls and design

Lower limb robotic devices, like prostheses and orthosis, are required to work closely with human limbs, and thus an effective control framework and reliable design are both critical. This dissertation presents novel methods to control a DC powered knee prosthesis, a pneumatic prosthesis, and the progress of controlling a multifunctional orthosis. Moreover, this dissertation also presents a novel pneumatic knee prosthesis design. A novel high-level controller controls the DC powered knee prosthesis by utilizing the Electromyography (EMG) with biomechanical model. The controller combines an active control component that reflects the wearer's motion intention, with a reactive control component that implements the controllable impedance critical to the safe and stable interaction. The effectiveness of the proposed control approach is demonstrated through the experimental results for arbitrary free swing and level walking. A sliding mode low-level controller is applied to control the pneumatic prosthesis to overcome the highly nonlinearity from the properties of pneumatic muscle and the design of prosthesis. The effectiveness of the controller is demonstrated though experiments. The progress of making a complete control algorithm for a multifunctional orthosis consists of two major parts. One is the user movement classification methods. There are a total of three classifiers: the walk-to-stop classifier, the speed-changing classifier, and the movement start classifier, which includes climbing up a stair, climbing down a stair and level walking. The classification rate of all three qualifiers is 90% or more. The second major part of the research is high-level controllers for different functions. A high-level fuzzy impedance controller, which increases the flexibility of a regular impedance controller, has been developed for speed adaptive walking control. The effectiveness of the controller is demonstrated through simulation. A novel knee prosthesis design which utilizes the rope pulley mechanism and slider crank mechanism. In the pulley design for the rope pulley mechanism, a superellipse pulley is chosen to give more variation. The parameters in those mechanisms and the prosthesis are optimized, so that the knee torque from the prosthesis is close to that in a biological leg. The design also reserves space for the components of an ankle prosthesis. (Published By University of Alabama Libraries

<i>spl</i> mutations reduce the expression of genes involved in floral induction and floral meristem identity.

<p>qRT-PCR analysis of transcripts isolated from shoot apices of 11 day-old plants. Values are normalized to Col, and represent the mean from 2 biological replicates ± SE.</p

The effect of <i>SPL</i> mutations on vegetative and reproductive development.

<p>The effect of <i>SPL</i> mutations on vegetative and reproductive development.</p

miR172 levels are reduced in <i>spl</i> mutants.

<p>The abundance of (A) pri-miR172b, (B) miR172 and (C) <i>SPL3</i> and <i>SPL5</i> mRNA in the shoot apices of 16-day-old <i>spl</i> mutants. Values are the average of 3 biological replicates, ± SE.</p

Elevated <i>SPL</i> expression inhibits adventitious root production.

<p>(A) Roots originating from the hypocotyl of Col, transgenic, and <i>spl</i> mutant seedlings after removal of the primary root. (B) The number of adventitious roots produced by the genotypes illustrated in (A). * Significantly different from Col, p<0.05.</p