Human activity selectively impacts the ecosystem roles of parrotfishes on coral reefs

Around the globe, coral reefs and other marine ecosystems are increasingly overfished. Conventionally, studies of fishing impacts have focused on the population size and dynamics of targeted stocks rather than the broader ecosystem-wide effects of harvesting. Using parrotfishes as an example, we show how coral reef fish populations respond to escalating fishing pressure across the Indian and Pacific Oceans. Based on these fish abundance data, we infer the potential impact on four key functional roles performed by parrotfishes. Rates of bioerosion and coral predation are highly sensitive to human activity, whereas grazing and sediment removal are resilient to fishing. Our results offer new insights into the vulnerability and resilience of coral reefs to the ever-growing human footprint. The depletion of fishes causes differential decline of key ecosystem functions, radically changing the dynamics of coral reefs and setting the stage for future ecological surprises.     

Dstac is required for normal circadian activity rhythms in Drosophila

The genetic, molecular and neuronal mechanism underlying circadian activity rhythms is well characterized in the brain of Drosophila. The small ventrolateral neurons (s-LN_Vs) and pigment dispersing factor (PDF) expressed by them are especially important for regulating circadian locomotion. Here we describe a novel gene, Dstac, which is similar to the stac genes found in vertebrates that encode adaptor proteins, which bind and regulate L-type voltage-gated Ca²⁺ channels (CaChs). We show that Dstac is coexpressed with PDF by the s-LN_Vs and regulates circadian activity. Furthermore, the L-type CaCh, Dmca1D, appears to be expressed by the s-LN_Vs. Since vertebrate Stac3 regulates an L-type CaCh we hypothesize that Dstac regulates Dmca1D in s-LN_Vs and circadian activity.     

Human rabaptin-5 is selectively cleaved by caspase-3 during apoptosis

We have previously shown that Xenopus rabaptin-5 is cleaved in apoptotic extracts, with a concomitant reduction in the ability of these extracts to support endosomal membrane fusion (Cosulich, S. C., Horiuchi, H., Zerial, M., Clarke, P. R., and Woodman, P. G. (1997) EMBO J. 16, 6182-6191). In this report we demonstrate that caspase-dependent cleavage is a conserved feature of rabaptin-5. Human rabaptin-5 is cleaved at two sites (HSLD(379) and DESD(438)) in apoptotic HeLa extracts. Cleavage is effected by caspase-3, since it is prevented when caspase-3 activity is either inhibited by Ac-DEVD-CHO or removed by immunodepletion. Moreover, an identical pattern of cleavage is observed using recombinant caspase-3. The action of caspase-3 is highly selective; neither caspase-2 nor caspase-7 are able to cleave recombinant or cytosolic rabaptin-5. Caspase-dependent cleavage of rabaptin-5 generates two physically separated coiled coil-forming domains, the C-terminal of which retains the ability to bind the Rab5 exchange factor rabex-5.     

Cellular and biochemical mechanisms underlying circadian rhythms in vertebrates

Circadian clocks organize neural processes, such as motor activities, into near 24-hour oscillations and adaptively synchronize these rhythms to the solar cycle. Recently, the first mammalian clock genes have been found. Unpredicted diversity in signaling pathways and clock-controlled gating of signals that modulate timekeeping has been discovered. A diffusible clock output has been found to control some behavioral rhythms. Consensus is emerging that circadian mechanisms are conserved across phylogeny, but that mammals have developed a great complexity of controls.     

Neural control of circadian rhythms in plasma ACTH, plasma corticosterone and motor activity

The circadian rhythms for plasma ACTH and corticosterone (B), as well as motor activity, were explored in female rats after ocular enucleation (O-X), stereotaxic lesion of the suprachiasmatic nuclei (SCN-X) or of midbrain raphe nuclei (R-X), or both O-X and R-X, pharmacological blockade of the serotoninergic (5HT) system by pCPA, sometimes bypassed by 5-HTP, or 5-HT denervation of the SCN by local injection of 5,7-DHT. The three circadian rhythms explored responded quite differently to the treatments. In particular, the ACTH and B rhythms lost their usual close correlations. The amplitude and mean level of ACTH fluctuations were depressed after all treatments, but remained normal or were enhanced for B rhythm. ACTH rhythmicity actually was undetectable after SCN-X, pCPA and, in several rats, combined O-X and R-X, whereas persisting circadian and/or ultradian B and locomotor activity rhythms were always measured. The participation of the suprachiasmatic nuclei, the midbrain raphe nuclei and other possible 5-HT components in a complex circadian pacemaker system is discussed.     

Controlling the cortical actin motor

Actin is the essential force-generating component of the microfilament system, which powers numerous motile processes in eukaryotic cells and undergoes dynamic remodeling in response to different internal and external signaling. The ability of actin to polymerize into asymmetric filaments is the inherent property behind the site-directed force-generating capacity that operates during various intracellular movements and in surface protrusions. Not surprisingly, a broad variety of signaling pathways and components are involved in controlling and coordinating the activities of the actin microfilament system in a myriad of different interactions. The characterization of these processes has stimulated cell biologists for decades and has, as a consequence, resulted in a huge body of data. The purpose here is to present a cellular perspective on recent advances in our understanding of the microfilament system with respect to actin polymerization, filament structure and specific folding requirements.     

Human replication protein Cdc6 is selectively cleaved by caspase 3 during apoptosis

In eukaryotes, the initiation of DNA replication involves the ordered assembly on chromatin of pre-replicative complexes (pre-RCs), including the origin recognition complex (ORC), Cdc6, Cdt1 and the minichromosome maintenance proteins (MCMs). In light of its indispensable role in the formation of pre-RCs, Cdc6 binding to chromatin represents a key step in the regulation of DNA replication and cell proliferation. Here, we study the human Cdc6 (HuCdc6) protein during programmed cell death (apoptosis). We find that HuCdc6, but not HuOrc2 (a member of the ORC) or HuMcm5 (one of the MCMs), is specifically cleaved in several human cell lines induced to undergo apoptosis by a variety of stimuli. Expression of caspase-uncleavable mutant HuCdc6 attenuates apoptosis, delaying cell death. Therefore, an important function for cleavage of HuCdc6 is to prevent a wounded cell from replicating and to facilitate death.     

Effect of cortical extracellular GABA on motor response

Journal of Computational Neuroscience - To elucidate how the flattening of sensory tuning due to a deficit in tonic inhibition slows motor responses, we simulated a neural network model in which a...     

Human myosin Vc is a low duty ratio nonprocessive motor

There are three distinct members of the myosin V family in vertebrates, and each isoform is involved in different membrane trafficking pathways. Both myosin Va and Vb have demonstrated that they are high duty ratio motors that are consistent with the processive nature of these motors. Here we report that the ATPase cycle mechanism of the single-headed construct of myosin Vc is quite different from those of other vertebrate myosin V isoforms. K(ATPase) of the actin-activated ATPase was 62 microm, which is much higher than that of myosin Va ( approximately 1 mum). The rate of ADP release from actomyosin Vc was 12.7 s(-1), which was 2 times greater than the entire ATPase cycle rate, 6.5 s(-1). P(i) burst size was 0.31, indicating that the equilibrium of the ATP hydrolysis step is shifted to the prehydrolysis form. Our kinetic model, based on all kinetic data we determined in this study, suggests that myosin Vc spends the majority of the ATPase cycle time in the weak actin binding state in contrast to myosin Va and Vb. Consistently, the two-headed myosin Vc construct did not show processive movement in total internal reflection fluorescence microscope analysis, demonstrating that myosin Vc is a nonprocessive motor. Our findings suggest that myosin Vc fulfills its function as a cargo transporter by different mechanisms from other myosin V isoforms.     

Circadian rhythms of body temperature and motor activity in rodents their relationships with the light-dark cycle

In rodents, the alternation of light and dark is the main synchronizer of circadian rhythms. The entrainment abilities of the LD cycle could be estimated by experimental modifications of the photoperiod and by following the subsequent temporal distribution of a circadian rhythm. The rate of reentrainment of a rhythm is determined by the nature of the studied variable, by the direction (advance or delay) and the magnitude (or value) of the phase shift. In rodents, core body temperature and motor activity are known to be well synchronized with each other under L:D 12:12 and under constant conditions (LL or DD). There are clear evidences that the circadian pattern of motor activity is generated by two oscillators, one from dusk signal and the other from dawn signal. Whether the circadian rhythms of body temperature and motor activity are generated by a common circadian mechanism or controlled by separate ones still remains unknown. The purpose of this review is to summarize the results obtained on the circadian rhythms of body temperature and motor activity throughout the daily cycle in order to clarify the relationships between these two functions.     

Phase relationships between sleep-wake cycle and underlying circadian rhythms in Morningness-Eveningness

A shorter phase angle between habitual wake time and underlying circadian rhythms has been reported in evening types (E types) compared to morning-types (M types). In this study, phase angles were compared between 12 E types and 12 M types to verify if this difference was observed when the sleep schedule was relatively free from external social constraints. Subjects were selected according to their Morningness-Eveningness Questionnaire score (MEQ score). There were 6 men and 6 women in each group (ages 19-34 years), and all had a habitual sleep duration between 7 and 9 h. Sleep schedule was recorded by actigraphy and averaged over 7 days. Circadian phase was estimated by the hour of temperature minimum (T(min)) in a 26-h recording and by the timing of the onset of melatonin secretion (dim-light melatonin onset [DLMO]) measured in saliva samples. Phase angles were defined as the interval between phase markers and averaged wake time. Results showed that, in the present experimental conditions, phase angles were very similar in the 2 groups of subjects. However, results confirmed the previously reported correlation between phase and phase angle, showing that a later circadian phase was associated with a shorter phase angle. Gender comparisons showed that for a same MEQ score, women had an earlier DLMO and a longer phase angle between DLMO and wake time. Despite a significant difference in the averaged circadian phases between E-type and M-type groups, there was an overlap in the circadian phases of the subjects of the 2 groups. Further comparisons were made between the 2 circadian types, separately for the subgroups with overlapping or nonoverlapping circadian phases. In both subgroups, the significant difference between MEQ scores, bedtimes, and wake times were maintained in the expected direction. In the subgroup with nonoverlapping circadian phases, phase angles were shorter in E-type subjects, in accordance with previous studies. However, in the overlapping subgroup, phase angles were significantly longer in E types compared to M types. Results suggest that the morningness-eveningness preference identified by the MEQ score refers to 2 distinct mechanisms, 1 associated with a difference in circadian period and phase of entrainment and the other associated with chronobiological aspects of sleep regulation.     

Timing of cortical excitability changes during the reaction time of movements superimposed on tonic motor activity.

Seated subjects were instructed to react to an auditory cue by simultaneously contracting the tibialis anterior (TA) muscle of each ankle isometrically. Focal transcranial magnetic stimulation of the leg area of the motor cortex (MCx) was used to determine the time course of changes in motor-evoked potential amplitude (MEP) during the reaction time (RT). In one condition the voluntary contraction was superimposed on tonic EMG activity maintained at 10% of maximal voluntary contraction. In the other condition the voluntary contraction was made starting from rest. MEPs in the TA contralateral to the stimulation coil were evoked at various times during the RT in each condition. These were compared to the control MEPs evoked during tonic voluntary activity or with the subject at rest. The RT was measured trial by trial from the EMG activity of the TA ipsilateral to the magnetic stimulus, taking into account the nearly constant time difference between the two sides. The MEPs became far greater than control MEPs during the RT (mean = 332%, SD = 44 %, of control MEPs, P < 0.001) without any measurable change in the background level of EMG activity. The onset of this facilitation occurred on average 12.80 ms (SD = 7.55 ms) before the RT. There was no difference in the onset of facilitation between the two conditions. Because MEPs were facilitated without a change in the background EMG activity, it is concluded that this facilitation is specifically due to an increase of MCx excitability just before voluntary muscle activation. This conclusion is further reinforced by the observation that MEPs evoked by near-threshold anodal stimuli to the MCx were not facilitated during the RT, in contrast to those evoked by near-threshold transcranial magnetic stimulation. However, several observations in the present and previous studies indicate that MEP amplitude may be more sensitive to alpha-motoneuron activity than to motor cortical neuron activity, an idea that has important methodological implications.     

Time to task failure and motor cortical activity depend on the type of feedback in visuomotor tasks

The present study aimed to elucidate whether the type of feedback influences the performance and the motor cortical activity when executing identical visuomotor tasks. For this purpose, time to task failure was measured during position- and force-controlled muscular contractions. Subjects received either visual feedback about the force produced by pressing a force transducer or about the actual position between thumb and index finger. Participants were instructed to either match the force level of 30% MVC or the finger position corresponding to the thumb and index finger angle at this contraction intensity. Subjects demonstrated a shorter time to task failure when they were provided with feedback about their joint position (11.5 ± 6.2 min) instead of force feedback (19.2 ± 12.8 min; P = 0.01). To test differences in motor cortical activity between position- and force-controlled contractions, subthreshold transcranial magnetic stimulation (subTMS) was applied while executing submaximal (20% MVC) contractions. SubTMS resulted in a suppression of the first dorsal interosseus muscle (FDI) EMG in both tasks. However, the mean suppression for the position-controlled task was significantly greater (18.6 ± 9.4% vs. 13.3 ± 7.5%; P = 0.025) and lasted longer (13.9 ± 7.5 ms vs. 9.3 ± 4.3 ms; P = 0.024) compared to the force-controlled task. The FDI background EMG obtained without stimulation was comparable in all conditions. The present results demonstrate that the presentation of different feedback modalities influences the time to task failure as well as the cortical activity. As only the feedback was altered but not the mechanics of the task, the present results add to the body of evidence that suggests that the central nervous system processes force and position information in different ways.     

Developmental mechanisms underlying the generation of cortical interneuron diversity

GABAergic interneurons are critical components of cortical circuits. However, understanding their function has become extremely challenging because they constitute one of the most diverse groups of cells in the central nervous system. Indeed, cortical GABAergic interneurons are heterogeneous in so many different ways--morphology, molecular profiling, electrical properties--that even attempts to discern what parameters should be used to identify cortical interneuron subtypes have failed to generate broad consensus among experts in the field. The extent to which cortical interneuron diversity emerges during development is largely unknown, but it is likely that insights on how this process takes place may help us understand their role as integrative and synchronizing elements in cortical function. Here, we review recent data on how the large variety of distinct classes of cortical interneurons may arise during development.