Multicellular stalk-like structures in Saccharomyces cerevisiae

Stalk formation is a novel pattern of multicellular organization. Yeast cells which survive UV irradiation form colonies that grow vertically to form very long (0.5 to 3.0 cm) and thin (0.5 to 4 mm in diameter) multicellular structures. We describe the conditions required to obtain these stalk-like structures reproducibly in large numbers. Yeast mutants, mutated for control of cell polarity, developmental processes, UV response, and signal transduction cascades were tested and found capable of forming stalk-like structures. We suggest a model that explains the mechanism of stalk formation by mechanical environmental forces. We show that other microorganisms (Candida albicans, Schizosaccharomyces pombe, and Escherichia coli) also form stalks, suggesting that the ability to produce stalks may be a general property of microorganisms. Diploid yeast stalks sporulate at an elevated frequency, raising the possibility that the physiological role of stalks might be disseminating spores.     

Conditional copying fidelity in capuchin monkeys (Cebus apella).

In the last two decades, it became largely accepted that monkeys show little, if any, copying fidelity. However, some recent studies have begun to challenge this notion. To explore reasons for such contrary findings, we designed a foraging apparatus so that in each of two experiments with capuchin monkeys (Cebus apella), a model would demonstrate one of two alternative methods to obtain food. The apparatus had a V-shaped track on which a panel could be slid up left or right from the center to reveal food. In Experiment 1, food was located in a cup directly behind the center panel. In Experiment 2, sliding the panel left or right revealed food either in left or right ends of the V-track. Since this sliding movement led directly to one food location exclusive of the other, we predicted capuchins would show greater copying fidelity in this second Experiment. Instead, subjects were significantly more faithful to the model’s method in Experiment 1, which provided strong evidence of capuchins copying what they had observed. We suggest that the contrasting results of Experiment 1 may have occurred because capuchins prioritize exploratory behavior when alternative foraging locations are accessible. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Use of Visual, Acoustic, and Olfactory Information During Embedded Invertebrate Foraging in Brown Capuchins (Cebus apella).

Experiments were conducted to investigate which sensory cues are used by brown capuchins (Cebus apella) in embedded invertebrate foraging. The importance of visual, olfactory, and acoustic cues in such foraging was determined by presenting subjects with a stimulus log modified to block out given sensory cues. Experiment 1 was designed to investigate whether subjects could locate an invertebrate embedded in wood when only visual, acoustic, or olfactory information was available. Experiments 2 and 3 were designed to investigate extractive foraging behavior when two sensory cues were provided. It was hypothesized that the combination of visual and acoustic information would be necessary for subjects to successfully locate embedded invertebrates. Results indicated that subjects' performance was most successful when both visual and acoustic information was available. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Caulobacter and Asticcacaulis stalk bands as indicators of stalk age

The prosthecae (stalks) of dimorphic caulobacters of the genera Caulobacter and Asticcacaulis are distinguished among such appendages by the presence of disk-like components known as stalk bands. Whether bands are added to a cell's stalk(s) as a regular event coordinated with the cell's reproductive cycle has not been settled by previous studies. Analysis of the frequency of stalks with i, i + 1, i + 2, etc. bands 'among more than 7,000 stalks of Caulobacter crescentus revealed that in finite (batch) cultures (in which all offspring accumulate), the proportion of stalks with i + 1 hands was regularly 50% of the proportion of stalks with i bands. This implied that the number of bands correlated with the number of reproductive cycles completed by a stalked cell. In chemostat-maintained perpetual cultures, the proportion was greater than 50% because stalked cells, with their shorter reproductive cycle times, contributed a larger proportion of offspring to the steady-state population than did their swarmer siblings. In Asticcacaulis biprosthecum cells, which bear twin prosthecae, the twins on a typical cell possessed the same number of bands. For both genera, stalk bands provide a unique morphological feature that could be employed in an assessment of age distribution and reproductive dynamics within natural populations of these caulobacters.     

Self-control and tool use in tufted capuchin monkeys (Cebus apella).

Self-control is defined as forgoing immediate gratification to obtain a greater reward. Tool use may relate to self-control because both behaviors may require foresight and deliberate control over one's actions. The authors assessed 20 capuchin monkeys (Cebus apella) for the ability to delay gratification in a tool task. Subjects were given rod-shaped food items that could either be consumed immediately or be carried to an apparatus and used to extract a more preferred food. The authors found that some monkeys were able to exhibit self-control. Monkeys with relatively more tool use experience demonstrated the greatest levels of self-control. These results indicate that capuchins are capable of delaying gratification when a higher quality reinforcer is present and that tool experience can influence levels of self-control in this task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Developmental changes in manipulation in tufted capuchins (Cebus apella) from birth through 2 years and their relation to foraging and weaning.

This study examined the contributions of physical and sensorimotor development to manipulation in capuchins (Cebus apella) from birth to 2 years. Between months 1–6 and 7–12, manipulation increased significantly in frequency, in the proportion that was vigorous or required fine motor control, and in the proportion directed at portable objects. Fine motor control, moving objects in relation to the body, and stamina are largely in place by 12 months, after which little changed. All elements of the manipulative repertoire have appeared, and vigorous and dexterous activities have peaked before fully independent foraging. Emergence of permanent dentition and achievement of approximately half of adult body size accompany the attainment of fully independent foraging at 15 months. Thereafter, increasing strength and specific knowledge probably contribute more to changing foraging competence in young capuchins than do stamina and sensorimotor development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Monkeys (Macaca mulatta and Cebus apella) track, enumerate, and compare multiple sets of moving items.

Despite many demonstrations of numerical competence in nonhuman animals, little is known about how well animals enumerate moving stimuli. In this series of experiments, rhesus monkeys (Macaca mulatta) and capuchin monkeys (Cebus apella) performed computerized tasks in which they had to enumerate sets of stimuli. In Experiment 1, rhesus monkeys compared two sets of moving stimuli. Experiment 2 required comparisons of a moving set and a static set. Experiment 3 included human participants and capuchin monkeys to assess all 3 species' performance and to determine whether responding was to the numerical properties of the stimulus sets rather than to some other stimulus property such as cumulative area. Experiment 4 required both monkey species to enumerate subsets of each moving array. In all experiments, monkeys performed above chance levels, and their responses were controlled by the number of items in the arrays as opposed to nonnumerical stimulus dimensions. Rhesus monkeys performed comparably to adult humans when directly compared although capuchin performance was lower. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Primary motor cortex asymmetry is correlated with handedness in capuchin monkeys (cebus apella).

Humans exhibit a population-wide tendency toward right-handedness, and structural asymmetries of the primary motor cortex are associated with hand preference. Reported are similar asymmetries correlated with hand preference in a New World monkey (Cebus apella) that does not display population-level handedness. Asymmetry of central sulcus depth is significantly different between left-handed and right-handed individuals as determined by a coordinated bimanual task. Left-handed individuals have a deeper central sulcus in the contralateral hemisphere; right-handed individuals have a more symmetrical central sulcus depth. Cerebral hemispheric specialization for hand preference is not uniquely human and may be more common among primates in general. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ordinal judgments of symbolic stimuli by capuchin monkeys (Cebus apella) and rhesus monkeys (Macaca mulatta): The effects of differential and nondifferential reward.

Ordinal learning was investigated in capuchin monkeys (Cebus apella) and rhesus monkeys (Macaca mulatta). In Experiment 1, both species were presented with pairings of the Arabic numerals 0 to 9. Some monkeys were given food rewards equal to the value of the numeral selected and some were rewarded with a single pellet only for choosing the higher numeral within the pair. Both species learned to select the larger numeral, but only rhesus monkeys that were differentially rewarded performed above chance levels when presented with novel probe pairings. In Experiment 2, the monkeys were first presented with arrays of 5 familiar numerals (from the range 0 to 9) and then arrays of 5 novel letters (from the range A to J) with the same reward outcomes in place as in Experiment 1. Both species performed better with the numerals, suggesting that an ordinal sequence of all stimuli had been learned during Experiment 1, rather than a matrix of two-choice discriminations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cooperative problem solving by tufted capuchin monkeys (Cebus apella): Spontaneous division of labor, communication, and reciprocal altruism.

Using an experimentally induced cooperation task, the authors investigated whether tufted capuchin monkeys (Cebus apella) share the following 3 characteristics of cooperation with humans: division of labor, communication, and reciprocal altruism. In Experiment 1, the authors trained individual monkeys to perform the necessary sequence of actions for rewards and tested them in pairs to assess whether they could solve the task by spontaneously dividing the sequence of actions. All pairs solved this task. In Experiment 2, monkeys worked in the cooperation task and a task requiring no partner help. They looked at the partner significantly longer in the former task than in the latter, but communicative intent could not be determined. In Experiment 3, only 1 of 2 participants obtained a reward on each trial. Monkeys maintained cooperation when their roles were reversed on alternate trials. Their cooperative performances demonstrated division of labor; results suggest task-related communication and reciprocal altruism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dual regulation of the glycogen phosphorylase 2 gene Dictyostelium discoideum: the effects of DIF-1, cAMP, NH3 and adenosine

Cell differentiation in Dictyostelium results in the formation of two cell types, stalk and spore cells. The stalk cells undergo programmed cell death, whereas spore cells retain viability. The current evidence suggests that stalk cell differentiation is induced by Differentiation Inducing Factor (DIF), while spore cell differentiation occurs in response to cAMP. We have discovered the first developmentally regulated Dictyostelium gene, the glycogen phosphorylase gene 2 (gp2) gene, that can be induced by both DIF-1 and cAMP, suggesting the possibility of a new group of developmentally regulated genes that have DIF-1 and cAMP dual responsiveness. The gp2 gene was found to be expressed in both prestalk/stalk cells and prespore/spore cells. The DIF-1 competence of the gp2 gene required uninterrupted development, whereas the cAMP-competence for the gene required only starvation. Both DIF-1 and cAMP induction of the gene could be inhibited by NH3, a factor that is thought to act as a developmental signal in Dictyostelium. Another developmental signal, adenosine, was found to repress the DIF-1 induction of the gp2 gene. Two introns in the gp2 gene were examined for their involvement in the regulation of the gene, but no regulatory function was detected. A model for the regulation of the gp2 gene during the development is proposed.     

The role of the dynein stalk in cytoplasmic and flagellar motility

We have recently identified a microtubule binding domain within the motor protein cytoplasmic dynein. This domain is situated at the end of a slender 10-12 nm projection which corresponds to the stalks previously observed extending from the heads of both axonemal and cytoplasmic dyneins. The stalks also correspond to the B-links observed to connect outer arm axonemal dyneins to the B-microtubules in flagella and constitute the microtubule attachment sites during dynein motility. The stalks contrast strikingly with the polymer attachment domains of the kinesins and myosins which are found on the surface of the motor head. The difference in dynein's structural design raises intriguing questions as to how the stalk functions in force production along microtubules. In this article, we attempt to integrate the myriad of biochemical and EM structural data that has been previously collected regarding dynein with recent molecular findings, in an effort to begin to understand the mechanism of dynein motility.     

Learning and generalization of tool use by tufted capuchin monkeys (Cebus apella) in tasks involving three factors: Reward, tool, and hindrance.

We tested 4 captive tufted capuchin monkeys (Cebus apella) for their understanding of physical causality in variations of a 2-choice tool use task, 1 alternative of which allowed the monkeys easier access to food. Our monkeys, who had been adept at this task involving 2 items, that is, tool and food, quickly learned 3-term problems involving food, tool, and 1 type of hindrance (an obstacle or a trap, which could prevent success). All of the monkeys generalized their performance to new problems with the other type of hindrance and those with another familiar tool. These results suggest flexibility of their abilities to process complex physical information comprising 3 items in the environment, that is food–tool–hindrance spatial relationships. Such flexibility also implies that capuchin monkeys may possess rudimentary understanding of causal relationships involved in tool use. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Categorization of Above and Below Spatial Relations by Tufted Capuchin Monkeys (Cebus apella).

Using a matching-to-sample procedure, the researchers investigated tufted capuchins' (Cebus apella) ability to form categorical representations of above and below spatial relations. In Experiment 1, 5 capuchins correctly matched bar-dot stimuli on the basis of the relative above and below location of their constituent elements. The monkeys showed a positive transfer of performance both when the bar-dot distance in the two comparison stimuli differed from that of the sample and when the actual location of the matching stimulus and the nonmatching stimulus on the apparatus was modified. In Experiment 2, the researchers systematically changed the shapes of the located object (the dot) or the reference object (the horizontal bar). These manipulations did not affect the monkeys' performance. Overall, the data suggest that capuchins can form abstract, conceptual-like representations for above and below spatial relations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Auditory-visual cross-modal perception of communicative stimuli in Tufted Capuchin Monkeys (Cebus apella).

Research on cross-modal performance in nonhuman primates is limited to a small number of sensory modalities and testing methods. To broaden the scope of this research, the authors tested capuchin monkeys (Cebus apella) for a seldom-studied cross-modal capacity in nonhuman primates, auditory-visual recognition. Monkeys were simultaneously played 2 video recordings of a face producing different vocalizations and a sound recording of 1 of the vocalizations. Stimulus sets varied from naturally occurring conspecific vocalizations to experimentally controlled human speech stimuli. The authors found that monkeys preferred to view face recordings that matched presented vocal stimuli. Their preference did not differ significantly across stimulus species or other stimulus features. However, the reliability of the latter set of results may have been limited by sample size. From these results, the authors concluded that capuchin monkeys exhibit auditory-visual cross-modal perception of conspecific vocalizations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Production and activity of spore differentiation factors (SDFs) in Dictyostelium

SDF-1 and SDF-2 are peptides that promote terminal spore differentiation under submerged conditions. The present study shows that they accumulate differentially and are released during the development of wild-type cells and can promote spore formation in cells disaggregated from wild-type culminants. SDF-1 accumulates during the slug stage and is released in a single burst at the onset of culmination while SDF-2 accumulates during early culmination and is released in a single burst from mid-culminants. The effects of SDF-1 and SDF-2 on stalk cell formation in cell monolayers were investigated. SDF-1 by itself induces stalk cell formation in some strains and also synergizes with the stalk-cell-inducing factor, DIF-1. cAMP has an inhibitory effect on stalk cell formation when either DIF-1 or SDF-1 are present on their own but is almost not inhibitory when both are present. SDF-2 alone does not induce stalk cell formation and appears to inhibit the response to DIF-1. At the same time, it increases the extent of vacuolization of the stalk cells that are produced. We propose that the release of SDF-1 and then of SDF-2 may mark irreversible steps in the developmental programme associated, respectively, with culmination and spore maturation.     

Temperature-sensitive Gbeta mutants discriminate between G protein-dependent and -independent signaling mediated by serpentine receptors

Deletion of the single gene for the Dictyostelium G protein beta-subunit blocks development at an early stage. We have now isolated temperature-sensitive alleles of Gbeta to investigate its role in later development. We show that Gbeta is directly required for adenylyl cyclase A activation and for morphogenetic signaling during the entire developmental program. Gbeta was also essential for induction of aggregative gene expression by cAMP pulses, a process that is mediated by serpentine cAMP receptors (cARs). However, Gbeta was not required for cAR-mediated induction of prespore genes and repression of stalk genes, and neither was Gbeta needed for induction of prestalk genes by the differentiation inducing factor (DIF). cAMP induction of prespore genes and repression of stalk genes is mediated by the protein kinase GSK-3. GSK-3 also determines cell-type specification in insects and vertebrates and is regulated by the wingless/wnt morphogens that are detected by serpentine fz receptors. The G protein-dependent and -independent modes of cAR-mediated signaling reported here may also exist for the wingless/wnt signaling pathways in higher organisms.     

Partial support from a nonreplication: Comment on Roma, Silberberg, Ruggiero, and Suomi (2006).

A purported replication by P. G. Roma, A. Silberberg, A. M. Ruggiero, and S. J. Suomi (see record 2006-03207-008) of the authors' previous study (see record 2003-08401-002) claims to contradict their finding that capuchin monkeys (Cebus apella) refuse to exchange with an experimenter if their partner receives a superior reward. Roma et al. used no exchange task, however, or any other task. Roma et al. offered frustration as explanation of their findings, yet failed to statistically prove that the effect of frustration is stronger than that of inequity. They also misrepresented the dependent measure of the authors' study. Reanalysis of the authors' own data indicated no role of frustration, that is, no effect of previous experience with a superior reward. The authors conclude that Roma et al.'s study is not a replication and does not disprove the authors' findings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What perceptual rules do Capuchin Monkeys (Cebus Apella) follow in completing partly occluded figures?

Capuchin monkeys (Cebus apella) matched a variety of rodlike figures, distinguishable only by their central portions. The monkeys were then tested for perceptual completion rules by examining which comparison figures they would choose as matching the sample with the critical central portion occluded by a horizontal belt. In Experiment 1, the monkeys overwhelmingly chose a straight rod over disconnected rods and rods having irregular shapes at their center, irrespective of the presence-absence of common motion of visible parts of the samples. The monkeys chose a connected rod for relatable rods and disconnected rods for nonrelatable ones in Experiment 2. In Experiments 3 and 4, some of the monkeys chose rods specified by the global regularity of the contour, whereas others did not. Experiment 5 showed that humans and capuchin monkeys basically follow similar perceptual rules in completing occluded contours, but the global regularity rule may be stronger in humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)