Control of the mitotic exit network during meiosis

The mitotic exit network (MEN) is an essential GTPase signaling pathway that triggers exit from mitosis in budding yeast. We show here that during meiosis, the MEN is dispensable for exit from meiosis I but contributes to the timely exit from meiosis II. Consistent with a role for the MEN during meiosis II, we find that the signaling pathway is active only during meiosis II. Our analysis further shows that MEN signaling is modulated during meiosis in several key ways. Whereas binding of MEN components to spindle pole bodies (SPBs) is necessary for MEN signaling during mitosis, during meiosis MEN signaling occurs off SPBs and does not require the SPB recruitment factor Nud1. Furthermore, unlike during mitosis, MEN signaling is controlled through the regulated interaction between the MEN kinase Dbf20 and its activating subunit Mob1. Our data lead to the conclusion that a pathway essential for vegetative growth is largely dispensable for the specialized meiotic divisions and provide insights into how cell cycle regulatory pathways are modulated to accommodate different modes of cell division.     

Common features of neural activity during singing and sleep periods in a basal ganglia nucleus critical for vocal learning in a juvenile songbird

Reactivations of waking experiences during sleep have been considered fundamental neural processes for memory consolidation. In songbirds, evidence suggests the importance of sleep-related neuronal activity in song system motor pathway nuclei for both juvenile vocal learning and maintenance of adult song. Like those in singing motor nuclei, neurons in the basal ganglia nucleus Area X, part of the basal ganglia-thalamocortical circuit essential for vocal plasticity, exhibit singing-related activity. It is unclear, however, whether Area X neurons show any distinctive spiking activity during sleep similar to that during singing. Here we demonstrate that, during sleep, Area X pallidal neurons exhibit phasic spiking activity, which shares some firing properties with activity during singing. Shorter interspike intervals that almost exclusively occurred during singing in awake periods were also observed during sleep. The level of firing variability was consistently higher during singing and sleep than during awake non-singing states. Moreover, deceleration of firing rate, which is considered to be an important firing property for transmitting signals from Area X to the thalamic nucleus DLM, was observed mainly during sleep as well as during singing. These results suggest that songbird basal ganglia circuitry may be involved in the off-line processing potentially critical for vocal learning during sensorimotor learning phase.     

Reduction of oxygen by the electron transport chain of chloroplasts during assimilation of carbon dioxide.

In photosynthetically competent chloroplasts from spinach the quantum requirements for oxygen evolution during CO2 reduction were higher, by a factor often close to 1.5, than for oxygen evolution during reduction of phosphoglycerate. Mass spectrometer experiments performed under rate-limiting light indicated that an oxygen-reducing photoreaction was responsible for the consumption of extra quanta during carbon dioxide assimilation. Uptake of 18O2 during reduction of CO2 was considerably higher than could be accounted for by oxygen consumption during glycolate formation and by the Mehler reaction of broken chloroplasts which were present in the preparations of intact chloroplasts. The oxygen reducing reaction occurring during CO2 assimilation resulted in the formation of H2O2. This was indicated by a large stimulation of CO2 reduction by catalase, but not of phosphoglycerate reduction. Catalase could be replaced as a stimulant of photosynthesis by dithiothreitol or ascorbate, compounds known to react with superoxide radicals. There was no effect of dithiothreitol and ascorbate on phosphoglycerate reduction. A main effect of superoxide radicals and/or H2O2 was shown to be at the level of phosphoglycerate formation. Evidence for electron transport of oxygen was also obtained from 14CO2 experiments. The oxidation of dihydroxyacetonephosphate during a dark period or after addition of carbonyl cyanide p-trifluoromethoxyphenyl-hydrazone in the light was studied. The results indicated a link between the chloroplast pyridine nucleotide system and oxygen. Oxygen reduction during photosynthesis under conditions where light is rate limiting is seen as important in supplying the ATP which is needed for CO2 reduction but is not provided during electron transport to NADP. A mechanism is discussed which would permit proper distribution of electrons between CO2 and oxygen during photosynthesis.     

The Pleiotropic Function of Delta during Postembryonic Development of Drosophila Melanogaster

Analysis of the development of Delta (Dl) temperature-sensitive mutants pulsed at restrictive temperature during larval and pupal stages reveals multiple phenocritical periods during which reduction of Dl function affects viability and development of adult structures. Dl function is required during the third larval instar for post-pupal viability and during the first day of pupal development for viability through eclosion. Dl function is required biphasically for the development of sensory bristles. Earlier pulses lead to bristle multiplication and later pulses lead to bristle loss. The exact intervals during which multiplication and loss are induced vary for different bristles. Dl function is also required for development of most, if not all, cell types in the retina. Different pulses result in reduction in eye size, scarring, and glossiness, as well as multiplication and loss of interommatidial bristles. We also define intervals during which Dl function is required for aspects of leg and wing development. Phenocritical periods for Dl function are temporally coincident with those previously reported for Notch (N), consistent with the hypothesis that the proteins encoded by Dl and N interact throughout development to assure correct specification of cell fates in a variety of imaginal tissues.     

Response of the dTMP-synthesizing enzymes to differentiation processes in Physarum polycephalum

Synthesis of deoxythymidylate (dTMP) is a rate-limiting step in DNA synthesis; there are two main enzymes which are responsible for dTMP production, thymidylate synthetase (ts) and thymidine kinase (tk). Both enzymes were studied during several differentiation processes of the myxomycete Physarum polycephalum. In all stages of proliferation (microplasmodia, macroplasmodia, germinating microsclerotia and germinating spores) tk is the dominant enzyme in terms of activity, whereas ts is the predominant enzyme in quiescent stages (microsclerotia, sporangia, respectively spores); this is expressed by calculating the tk/ts ratio. This ratio is greater than 1 during proliferation and much less than 1 during quiescence. Our results clearly show that ts is the basic enzyme for dTMP production during all differentiation stages, whereas tk, if required, is shut on and represents an additional potential for dTMP synthesis during rapid proliferation.     

Inhibin may be involved in negative feedback in the prairie dog (Cynomys ludovicianus)

The changes in inhibin immunostaining in the gonads during the annual reproductive cycle of both sexes of the prairie dog are described. No inhibin immunostaining was found in primary or secondary follicles of the ovary. Theca and granulosa cells of preovulatory Graafian follicles found in January and February stained for inhibin. Corpora lutea of both pregnant and non-pregnant females stain more densely for inhibin than follicles. Inhibin staining is present in luteal cells for at least 4 months during regression, longer than detectable progesterone is secreted. Sertoli cells in the testes do not have inhibin immunostaining during recrudescence. These cells show light immunostain for inhibin during peak spermatogenic activity in January and February but stain more deeply during early regression of the testis. Stain is gradually lost in the next 4-5 months as the tubules close. Leydig cells and germ cells do not stain for inhibin at any stage of the annual cycle but interstitial cells and tunic cells stain during the breeding phase. The presence of immunochemical staining for inhibin in prairie dog gonads during regression suggests that inhibin is part of a negative feedback complex that includes progesterone in the female and testosterone or another androgen in the male. Negative feedback during regression may also cause gonadal inactivity.     

The Tangled1 gene is required for spatial control of cytoskeletal arrays associated with cell division during maize leaf development.

The cytoskeleton plays a major role in the spatial regulation of plant cell division and morphogenesis. Arrays of microtubules and actin filaments present in the cell cortex during prophase mark sites to which phragmoplasts and associated cell plates are guided during cytokinesis. During interphase, cortical microtubules are believed to influence the orientation of cell expansion by guiding the pattern in which cell wall material is laid down. Little is known about the mechanisms that regulate these cytoskeleton-dependent processes critical for plant development. Previous work showed that the Tangled1 (Tan1) gene of maize is required for spatial regulation of cytokinesis during maize leaf development but not for leaf morphogenesis. Here, we examine the cytoskeletal arrays associated with cell division and morphogenesis during the development of tan1 and wild-type leaves. Our analysis leads to the conclusion that Tan1 is required both for the positioning of cytoskeletal arrays that establish planes of cell division during prophase and for spatial guidance of expanding phragmoplasts toward preestablished cortical division sites during cytokinesis. Observations on the organization of interphase cortical microtubules suggest that regional influences may play a role in coordinating cell expansion patterns among groups of cells during leaf morphogenesis.     

单肺通气时低氧血症的预防的研究进展

单肺通气技术广泛用于开胸手术的麻醉处理,低氧血症是其主要并发症。低氧血症严重影响病人的正常生理功能,是麻醉医生和外科医生面临的重大挑战。因此,尽可能地预测,预防和处理低氧血症非常重要。术前肺功能、哪侧手术、肺血流灌注是其发生的重要预测因素。使用合理的通气方式,麻醉方法及药物会降低单肺通气时低氧血症的发生。本文综合分析了单肺通气时低氧血症的预防进展,以期减少其发生率。     

Autophagy and plant innate immunity: Defense through degradation

Autophagy is a process of bulk degradation and nutrient sequestration that occurs in all eukaryotes. In plants, autophagy is activated during development, environmental stress, starvation, and senescence. Recent evidence suggests that autophagy is also necessary for the proper regulation of hypersensitive response programmed cell death (HR-PCD) during the plant innate immune response. We review autophagy in plants with emphasis on the role of autophagy during innate immunity. We hypothesize a role for autophagy in the degradation of pro-death signals during HR-PCD, with specific focus on reactive oxygen species and their sources. We propose that the plant chloroplasts are an important source of pro-death signals during HR-PCD, and that the chloroplast itself may be targeted for autophagosomal degradation by a process called chlorophagy.     

Electromyographic analysis of rotator cuff muscles in patients with rotator cuff tendinopathy: A systematic review

The shoulder is inherently an unstable joint which heavily relies on the neuromuscular activation of the rotator cuff (RC) complex for stability during movement. Currently, there is no consensus regarding how the activity of RC muscles is affected among individuals with a RC tendinopathy (RCTe). This study reviewed the evidence of studies comparing the electromyographic (EMG) activity of any RC muscle of shoulders with a symptomatic RCTe to asymptomatic shoulders. Eight databases were searched. Data from 343 participants (201 symptomatic and 209 asymptomatic shoulders) were analyzed from 10 out of 402 included studies. Strong evidence for the infraspinatus and supraspinatus during isometric contractions and limited evidence for the supraspinatus and infraspinatus during isokinetic contractions suggest that the muscular activity is not altered among individuals with a RCTe during these types of contraction. Very limited evidence indicates reduced muscle activity for the infraspinatus and subscapularis in the presence of a RCTe during isotonic contractions, and no alterations for the supraspinatus or teres minor were identified. Lastly, conflicting to moderate evidence suggests alterations in RC muscle activity during unrestrained movements and swimming. These findings indicate that EMG deficits associated with a RCTe can best be appreciated during unrestrained movements.     

Trunk muscle activity during stability ball and free weight exercises

The purpose of this investigation was to compare trunk muscle activity during stability ball and free weight exercises. Nine resistance-trained men participated in one testing session in which squats (SQ) and deadlifts (DL) were completed with loads of approximately 50, 70, 90, and 100% of one-repetition maximum (1RM). Isometric contractions during 3 stability ball exercises (quadruped (QP), pelvic thrust (PT), ball back extension (BE)) were also completed. During all exercises, average integrated electromyography (IEMG) from the rectus abdominus (RA), external oblique (EO), longissimus (L1) and multifidus (L5) was collected and analyzed. Results demonstrate that when expressed relative to 100% DL 1RM, muscle activity was 19.5 +/- 14.8% for L1 and 30.2 +/- 19.3% for L5 during QP, 31.4 +/- 13.4% for L1 and 37.6 +/- 12.4% for L5 during PT, and 44.2 +/- 22.8% for L1 and 45.5 +/- 21.6% for L5 during BE. IEMG of L1 during SQ and DL at 90 and 100% 1RM, and relative muscle activity of L5 during SQ and DL at 100% 1RM was significantly greater (P < or = 0.05) than in the stability ball exercises. Furthermore, relative muscle activity of L1 during DL at 50 and 70% 1RM was significantly greater than in QP and PT. No significant differences were observed in RA and EO during any of the exercises. In conclusion, activity of the trunk muscles during SQs and DLs is greater or equal to that which is produced during the stability ball exercises. It appears that stability ball exercises may not provide a sufficient stimulus for increasing muscular strength or hypertrophy; consequently, the role of stability ball exercises in strength and conditioning programs is questioned. SQs and DLs are recommended for increasing strength and hypertrophy of the back extensors.     

The knee joint center of rotation is predominantly on the lateral side during normal walking

The purpose of this study was to test the hypothesis of whether the center of rotation (COR) in the transverse plane of the knee is in the medial side during normal walking in a manner similar to that previously described during non-ambulatory activities. The kinematics for normal knees was obtained from 46 knees during normal walking using the point cluster technique. The COR of the medial-lateral axis of the femur relative to the tibia was determined during the stance phase of walking. The hypothesis that the COR is in the medial side during stance was not supported by this study. The average COR during the stance phase of walking was in the lateral compartment for all 46 knees. In addition, the instantaneous COR occurred on the medial side on average <25% of the time during the stance phase. Thus, while the COR is predominantly on the lateral side of the knee during walking, the normal function of the knee during walking is associated with both lateral and medial pivoting. These results also demonstrate the importance of describing knee kinematics in the context of a specific activity or the constraints of the test conditions.     

Thyroid function in pregnancy

Iodine is required for the production of thyroid hormones. Normal thyroid function during pregnancy is important for both the mother and developing fetus. This review discusses the changes in thyroid physiology that occur during pregnancy, the significance of thyroid function tests and thyroid antibody titers assessed during pregnancy, and the potential obstetric complications associated with maternal hypothyroidism.     

A requirement for ARF6 during the completion of cytokinesis

During cancer development, coordinated changes in cell motility and cell cycle progression are required for the gradual transformation of normal cells into cancer cells. Previous studies have shown that ARF6 is a critical regulator of epithelial cell integrity and motility via its role in membrane movement and actin-based cytoskeletal remodeling. Recently, we have found that ARF6 also plays a role during cell division. It localizes to the cleavage furrow and midbody of cells during mitosis, and its activity is regulated during cytokinesis. Here, we investigate the requirement for ARF6 during mitosis and find that depletion of ARF6 using RNA interference disrupts the completion of cytokinesis. This finding demonstrates that ARF6 is essential during the final stages of cytokinesis. In addition, we have identified Ku70, a DNA-binding protein that is required for DNA damage repair, as a new ARF6-interacting protein and found that it is part of a complex with ARF6, especially during mitosis. These results clarify the importance of ARF6 activity during cytokinesis and begin to reveal other molecules that may contribute to the function of ARF6.     

Circadian regulation of cGMP-gated cationic channels of chick retinal cones. Erk MAP Kinase and Ca2+/calmodulin-dependent protein kinase II

cGMP-gated channels are essential for phototransduction in the vertebrate retina. Here we show that the affinity of these channels for cGMP in chick cones is substantially higher during the subjective night than during the subjective day. This effect persists in constant environmental conditions after entrainment to 12:12 hr light-dark cycles in vitro or in ovo. Circadian modulation of ligand affinity is a posttranslational effect and is driven by rhythms in the activities of two protein kinases: Erk and Ca2+/calmodulin-dependent protein kinase II (CaMKII). Erk is maximally active during the subjective night, whereas CaMKII is maximally active during the subjective day. Acute inhibition of these signaling pathways causes phase-dependent changes in the affinity of the channels for cGMP.     

Ovarian growth,induced by eyestalk ablation during the prebreeding season,is not normal in the crab,Paratelphusa hydrodromous (Herbst)

In Calicut populations of P. hydrodromous, the ovary is not refractory during September—November of the prebreeding season; it is inhibited from developing apparently by a gonad-inhibiting hormone(s) contained in the eyestalks. The prevalent tendency in Paratelphusa during the prebreeding season is to reproduce, and not to moult. The precocious ovarian growth induced by eyestalk removal during this season is biochemically impoverished, possibly due to uneven oocyte development, which in turn may be caused by the unpreparedness of a section of the population of oocytes for vitellogenesis. The ovary appears to have to pass through a period of oogonial proliferation under the influence of the moult-precipitating hormones during the moulting season, and subsequently through a period of oocyte differentiation during the prebreeding season, for normal vitellogenesis during the breeding season.     

The Yin and Yang of centromeric cohesion of sister chromatids: mitotic kinases meet protein phosphatase 2A

Accurate chromosome segregation during meiosis and mitosis is essential for the maintenance of genomic stability. Defects in the regulation of chromosome segregation during division predispose cells to undergo mitotic catastrophe or neoplastic transformation. Cohesin, a molecular glue holding sister chromatids together, is removed from chromosomes in a stepwise fashion during mitosis and meiosis. Cohesin at centromeres but not on chromosome arm remains intact until anaphase onset during early mitosis and the initiation of anaphase II during meiosis. Several recent studies indicate that the activity of protein phosphatase 2A is essential for maintaining the integrity of centromeric cohesin. Shugoshin, a guardian for sister chromatid segregation, may cooperate with and/or mediate PP2A function by suppressing the phosphorylation status of centromeric proteins including cohesin.     

Regulation of R7 and R8 differentiation by the spalt genes

Photoreceptor development begins in the larval eye imaginal disc, where eight distinct photoreceptor cells (R1-R8) are sequentially recruited into each of the developing ommatidial clusters. Final photoreceptor differentiation, including rhabdomere formation and rhodopsin expression, is completed during pupal life. During pupation, spalt was previously proposed to promote R7 and R8 terminal differentiation. Here we show that spalt is required for proper R7 differentiation during the third instar larval stage since the expression of several R7 larval markers (prospero, enhancer of split mdelta0.5, and runt) is lost in spalt mutant clones. In R8, spalt is not required for cell specification or differentiation in the larval disc but promotes terminal differentiation during pupation. We show that spalt is necessary for senseless expression in R8 and sufficient to induce ectopic senseless in R1-R6 during pupation. Moreover, misexpression of spalt or senseless is sufficient to induce ectopic rhodopsin 6 expression and partial suppression of rhodopsin 1. We demonstrate that spalt and senseless are part of a genetic network, which regulates rhodopsin 6 and rhodopsin 1. Taken together, our results suggest that while spalt is required for R7 differentiation during larval stages, spalt and senseless promote terminal R8 differentiation during pupal stages, including the regulation of rhodopsin expression.     

Different pathways of DNA synthesis are operative in the fat body of Spodoptera litura (insecta) during larval and pupal development

In Spodoptera litura, the DNA content of the fat body increases during the last larval instar. Radiolabelling studies reveal high degree of H3-thymidine incorporation in the fat cell DNA, during last larval stage of development. At prepupal stage the DNA synthesised during larval development is degraded, at least partially and the resultant nucleotides are most likely used as building blocks for the fat cell DNA synthesis during pupal development and pupal-adult metamorphosis, because very little H3 -thymidine injected into pupae is incorporated in DNA, though in fact, significant amount of DNA is synthesised during this period.     

Cytoskeletal mechanisms of neuronal degeneration

The cytoskeleton is the major intracellular determinant of neuronal morphology and is required for fundamental processes during the development and maintenance of a neuron. Thus, it is not surprising that many neurodegenerative diseases including Alzheimer's disease and amyotrophic lateral sclerosis (motor neuron disease) are characterized by typical abnormalities in the organization of the cytoskeleton. However, the role of the cytoskeletal changes during the development of the disease, e.g., whether they have a causative role during neuronal degeneration or represent an epiphenomenon of neurons that degenerate by other means, is still disputed. In this review, recent results on the development and the role of cytoskeletal abnormalities during neurodegenerative diseases are discussed and a mechanistic framework for the involvement of cytoskeletal changes during neurodegenerative processes is presented.