Mechano-chemical signaling in F9 cells

We investigated the molecular mechanism by which cells recognize and respond to physical forces in their local environment. Using a model system, to study wild type mouse F9 embryonic carcinoma cells, we examined how these cells sense mechanical stresses and translate them into biochemical responses through their cell surface receptor integrin and via the focal adhesion complex (FAC). Based on studies that show that many signal transducing molecules are immobilized on the cytoskeleton at the site of integrin binding within the focal adhesion complex, we found a time-dependent increase of focal adhesion kinase (pp125(FAK)) phosphorylation possibly due to protein kinase C (PKC) activation as well as protein kinase A (PKA) activity increase upon cell adhesion/spreading. These studies provide some insight into intracellular mechano-chemical signaling.     

The CRISPR/Cas9 system sheds new lights on the biology of protozoan parasites

Applied Microbiology and Biotechnology - The CRISPR/Cas9 system, a natural defence system of bacterial organisms, has recently been used to modify genomes of the most important protozoa parasites....     

Generation of variants of a motor act in a modular and hierarchical motor network

BACKGROUND: Most motor systems can generate a variety of behaviors, including categorically different behaviors and variants of a single motor act within the same behavioral category. Previous work indicated that many pattern-generating interneuronal networks may have a modular organization and that distinct categories of behaviors can be generated through flexible combinations of a small number of modules or building blocks. However, it is unclear whether and how a small number of modules could possibly generate a large number of variants of one behavior. RESULTS: We show that the modular feeding motor network of Aplysia mediates variations in protraction duration in biting-like programs. Two descending commands are active during biting behavior and trigger biting-like responses in a semiintact preparation. In the isolated CNS, when activated alone, the two commands produce biting-like programs of either long or short protraction duration by acting specifically on two modules that have opposite effects on protraction duration. More importantly, when coactivated at different frequencies, the two commands produce biting programs with an intermediate protraction duration. CONCLUSIONS: It was previously hypothesized that behavioral variants may be produced by combining different activity levels of multiple descending commands. Our data provide direct evidence for such a scheme and show how it is implemented in a modularly organized network. Thus, within a modular and hierarchical architecture, in addition to generating different categories of behavior, a small number of modules also efficiently implements variants of a single behavior.     

Orientation of Aplysia californien to distant food sources

Summary The behavior of the marine mollusc Aplysia was examined under different experimental conditions designed to determine the food searching strategy of the animals. In a small, open field tank with still water, the animals took an average of 42 min to find a piece of seaweed, even though the stimulus was never located more than 30 cm away from the animal. Observations of the animals indicated that their search was not directed, without a clear tendency towards the food, and during the course of a search, they often crawled through most of the area of the tank. The search time, the distance travelled, and the strategy of the search of the animals was similar for different types of seaweed. If animals were aroused into activity by the presence of seaweed extract, the time for them to contact a piece of odorless glass fiber paper in the open field was not significantly different than that for a piece of seaweed. The probability at which the animals contacted the seaweed, as a function of the distance travelled, resembled the detection probability determined according to a theory of random search. We thus propose that the aroused animals move in a random pattern until they are very close to the food. This strategy can be advantageous in still water since chemicals do not provide distinct gradients that can serve as cues for chemotactic orientation from distances greater than a few centimeters from the source.In a Y-maze in still water, Aplysia did not perform above chance in selecting the arm that contained the seaweed. In streaming water, the animals entered the arm that contained seaweed significantly above chance only if a large piece of seaweed was used, so as to provide a very strong stimulus. Similarly, presentation of a high concentration of glutamate or a high concentration of seaweed extract to one side of the animal could evoke turning towards the stimulus. In the Y-maze, animals that repeatedly entered and exited both arms before making a choice, performed better than those that went directly into one arm.We conclude that chemical food stimuli can evoke directed orientation only when the animal is very close to the stimulus (within a few centimeters, at most). For Aplysia, the role of distant chemical stimuli may not be to guide their orientation, but rather to evoke the food-induced arousal state. In this behavioral state, several behaviors, such as locomotion are altered, and these changes may provide the basis for locating food from a distance.Abbreviation SWE seaweed extract     

The stimulus control of biting inAplysia

Summary A number of different parameters of the biting response ofAplysia californica were examined while varying either the strength of excitatory stimuli that elicit biting, or the strength of inhibitory stimuli that suppress biting and produce satiation. Response amplitude, response latency and the interresponse interval of repetitive responses were the parameters investigated. In individual animals as well as in the mean data, all parameters of the biting response were found to be affected in a graded manner when the concentration of seaweed extract was varied, and when animals were fed to different levels of satiation. Feeding animals with non-nutritive bulk produced graded effects similar to those seen when animals were fed with seaweed. These results indicate that the biting response is modulated in a graded manner by external stimuli which elicit the response, as well as by internal stimuli which produce satiation.We would like to thank L. Eli Bronner for assistance in collecting the data, S. Hauser and K. Hilten for assistance with the illustrations, and T. Carew, V. Castellucci, and E. Kandel for comments on earlier drafts of this paper. This research was supported by NINCDS grant NS 12492, by P.H.S. Predoctoral Training Grant to the Department of Physiology, New York University Medical School, 71176-234, and by Sloan Foundation 360-3070-2772.     

Trisomy 18 in neonates: prenatal diagnosis, clinical features, therapeutic dilemmas and outcome

The study aimed to analyse the clinical courses of aggressively treated neonates with cytogenetically confirmed trisomy 18, with special attention focused on the efficiency of prenatal diagnostics, associated malformations, therapeutic dilemmas and outcomes. We investigated retrospectively the data concerning 20 neonates with trisomy 18, admitted to the Neonatal Intensive Care Unit (NICU) in Katowice between January 2000 and February 2005. Their birth weights ranged from 650 g to 2400 g, mean 1812 g; gestational age ranged from 27 to 42 weeks, median 38 weeks. Intrauterine growth retardation was noticed in 90% of neonates. Trisomy 18 was suspected prenatally in 40% of cases. Most (80%) of newborns were delivered by caesarean section (92% of neonates with prenatally unrecognized chromosomal defects, 62% of neonates with trisomy 18 suspicion) and 70% of infants needed respiratory support immediately after birth. Cardiac defects were present in 95%, central nervous system malformations in 65%, severe anomalies of digestive system or abdominal wall in 25% of patients. Nine surgical operations were performed during hospitalization (4 were palliative cardiac surgeries). Six patients (30%) survived the neonatal period and were discharged from the NICU. The median survival of the neonates who died was 20 days. In 4 cases cardiac problems implicated their death; in others, deaths were attributed to multiorgan failure, prematurity and/or infection. Further improvement of efficiency of prenatal ultrasound screening for diagnosis of trisomy 18 in the fetus is necessary. A lack of prenatal diagnosis of trisomy 18 in the fetus results in a high rate of unnecessary caesarean sections in these pregnancies. Despite the aggressive treatment most neonates with trisomy 18 died during the neonatal period. The majority of deaths were attributed to cardiorespiratory and multiorgan failure. Concerning the poor prognosis, prompt karyotyping (using FISH) of clinically suspected trisomy 18 is very important, because many invasive procedures and surgeries may then be avoided.     

Urotensin II in Invertebrates: From Structure to Function in Aplysia californica

Neuropeptides are ancient signaling molecules that are involved in many aspects of organism homeostasis and function. Urotensin II (UII), a peptide with a range of hormonal functions, previously has been reported exclusively in vertebrates. Here, we provide the first direct evidence that UII-like peptides are also present in an invertebrate, specifically, the marine mollusk Aplysia californica. The presence of UII in the central nervous system (CNS) of Aplysia implies a more ancient gene lineage than vertebrates. Using representational difference analysis, we identified an mRNA of a protein precursor that encodes a predicted neuropeptide, we named Aplysia urotensin II (apUII), with a sequence and structural similarity to vertebrate UII. With in-situ hybridization and immunohistochemistry, we mapped the expression of apUII mRNA and its prohormone in the CNS and localized apUII-like immunoreactivity to buccal sensory neurons and cerebral A-cluster neurons. Mass spectrometry performed on individual isolated neurons, and tandem mass spectrometry on fractionated peptide extracts, allowed us to define the posttranslational processing of the apUII neuropeptide precursor and confirm the highly conserved cyclic nature of the mature neuropeptide apUII. Electrophysiological analysis of the central effects of a synthetic apUII suggests it plays a role in satiety and/or aversive signaling in feeding behaviors. Finding the homologue of vertebrate UII in the numerically small CNS of an invertebrate animal model is important for gaining insights into the molecular mechanisms and pathways mediating the bioactivity of UII in the higher metazoan.     

Predicting adaptive behavior in the environment from central nervous system dynamics

To generate adaptive behavior, the nervous system is coupled to the environment. The coupling constrains the dynamical properties that the nervous system and the environment must have relative to each other if adaptive behavior is to be produced. In previous computational studies, such constraints have been used to evolve controllers or artificial agents to perform a behavioral task in a given environment. Often, however, we already know the controller, the real nervous system, and its dynamics. Here we propose that the constraints can also be used to solve the inverse problem--to predict from the dynamics of the nervous system the environment to which they are adapted, and so reconstruct the production of the adaptive behavior by the entire coupled system. We illustrate how this can be done in the feeding system of the sea slug Aplysia. At the core of this system is a central pattern generator (CPG) that, with dynamics on both fast and slow time scales, integrates incoming sensory stimuli to produce ingestive and egestive motor programs. We run models embodying these CPG dynamics--in effect, autonomous Aplysia agents--in various feeding environments and analyze the performance of the entire system in a realistic feeding task. We find that the dynamics of the system are tuned for optimal performance in a narrow range of environments that correspond well to those that Aplysia encounter in the wild. In these environments, the slow CPG dynamics implement efficient ingestion of edible seaweed strips with minimal sensory information about them. The fast dynamics then implement a switch to a different behavioral mode in which the system ignores the sensory information completely and follows an internal "goal," emergent from the dynamics, to egest again a strip that proves to be inedible. Key predictions of this reconstruction are confirmed in real feeding animals.     

From precursor to final peptides: a statistical sequence-based approach to predicting prohormone processing

Predicting the final neuropeptide products from neuropeptides genes has been problematic because of the large number of enzymes responsible for their processing. The basic processing of 22 Aplysia californica prohormones representing 750 cleavage sites have been analyzed and statistically modeled using binary logistic regression analyses. Two models are presented that predict cleavage probabilities at basic residues based on prohormone sequence. The complex model has a correct classification rate of 97%, a sensitivity of 97%, and a specificity of 96% when tested on the Aplysia dataset.     

Motor program selection in simple model systems

In recent years, studies of molluscan and crustacean feeding circuits have greatly expanded our knowledge of how the nervous system selects specific behaviors. Increasing use of neurobehavioral studies, and examination of the roles of identified command-like or influential neurons have narrowed the gap between knowledge of circuit connectivity and understanding of the normal behavioral functions of these circuits.