Artificial neural networks can distinguish novice and expert strategies during complex problem solving.

OBJECTIVE: To determine whether expert problem-solving strategies can be identified within a large number of student performances of complex medical diagnostic simulations. METHODS: Self-organizing artificial neural networks were trained to categorize the performances of infectious disease subspecialists on six computer-based clinical diagnostic simulation that used the sequence of diagnostic tests requested as the input data. Six hundred seventy-six student solutions to these problems were presented to these trained neural networks to determine which, if any, of the student solutions represented those of the experts. RESULTS: For each simulation, the expert performances clustered around one dominant output neurode, indicating that there were common problem-specific features associated with the experts' problem-solving performances. When the performances of students who also made correct problem diagnoses were tested on these expert-trained neural networks, 17% were classified as representing expert strategies, indicating that expert performance was a somewhat rare and inconsistent occurrence among the students. CONCLUSIONS: The ability to identify a small number of expert-like strategies within a large body of student performances may provide an opportunity to study the dynamics of complex learning at both individual and population levels as well as the emergence of medical diagnostic expertise.

Artificial neural network comparison of expert and novice problem-solving strategies.

The successful strategies of second-year medical students were electronically captured from computer-based simulations in immunology and infectious disease and were used to train artificial neural networks for the rapid classification of subsequent students' and experts' strategies on these problems. Such networks could categorize problem solutions of other students as successful or nonsuccessful > 85% of the time. These neural networks, however, performed poorly (as low as 13%) when classifying experienced immunologists' or internists' successful performances, suggesting an ability to distinguish between novice and expert strategies. The neural networks also identified a group of students who framed the infectious disease problems correctly, but had difficulty discriminating between differential diagnoses.

Characterization of translation systems in vitro from three developmental stages of Strongylocentrotus purpuratus.

We have developed and characterized cell-free systems active in translation from unfertilized eggs, 30-min zygotes and hatched blastulae of the sea urchin Strongylocentrotus purpuratus. The ion concentrations selected for preparation of the lysates were 150 mM-K+, 40 mM-Na+, 40 mM-Cl-, 5 x 10(-7) M free Ca2+ and 1 mM free Mg2+. It was necessary to include the ribonuclease inhibitor RNas in the preparations to obtain full activity consistently. The pH optimum was 7.2 and was extremely sharp for the three S. purpuratus lysates. The temperature optima of the three lysates were remarkably similar to those of the intact unfertilized egg and embryos. Lysates from unfertilized egg and 30-min zygotes showed a temperature optimum at 15 degrees C. The hatched blastula lysate showed a broader temperature optimum with a shift to about 20 degrees C. The optimized lysates incorporated radiolabelled amino acids into polypeptides for up to 90 min. The polypeptides synthesized ranged in Mr from 200,000 to 20,000, suggesting that the mRNA in the lysates was intact and capable of directing the synthesis of complete polypeptides. Furthermore, the three lysates were capable of initiation, as demonstrated by inhibition of initiation using the inhibitors edeine and 7-methylguanosine 5'-triphosphate (m7GTP). At 15 degrees C, the transit times for the three lysates were: unfertilized egg, 40 min; 30-min zygotes and hatched blastula lysates, 20 min. These transit times are similar to those of intact eggs and embryos, and significantly, reflect the two-fold increase in elongation rate seen following fertilization in intact embryos. Thus, these lysates display many features and characteristic responses typical of intact eggs and embryos, indicating that the lysates should be useful tools for the analysis of translation control in early embryogenesis.

Translational control in early sea urchin embryogenesis: initiation factor eIF4F stimulates protein synthesis in lysates from unfertilized eggs of Strongylocentrotus purpuratus.

We have used cell-free translation systems from unfertilized eggs and embryos of the sea urchin Strongylocentrotus purpuratus to analyze the mechanisms limiting protein synthesis in early embryogenesis. Unfertilized egg lysates supplemented with nuclease-treated reticulocyte lysate were stimulated 2-4-fold in incorporation of radioactive amino acid into protein. Thirty-minute zygote lysates supplemented in this way were not stimulated. These results suggested that a component limiting translation in the unfertilized egg lysate was provided by the nuclease-treated lysate and that this component was no longer limiting protein synthesis following fertilization. In view of these results, partially fractionated lysates and individual purified translational components from mammalian cells were tested for stimulation of the unfertilized egg lysate. A 1000000g supernatant devoid of ribosomal subunits also stimulated the unfertilized egg lysate. Thus, the stimulation was not due to the addition of active ribosomal subunits but to soluble elements in the reticulocyte lysate. Of the soluble components tested, only the cap-binding protein complex eIF4F caused a dramatic stimulation of the unfertilized egg lysate (2-3.5-fold). The 30-min zygote lysate was not stimulated by eIF4F or by any of the other components tested, supporting the hypothesis that a block in the translational machinery is removed at fertilization. A rabbit reticulocyte shift assay was used to analyze whether mRNA is limiting in early development. When unfertilized egg lysate was added to the shift assay, there was no shift in radioactivity from 43S to 80S complexes, indicating the unfertilized egg mRNA is not available for translation.(ABSTRACT TRUNCATED AT 250 WORDS)

Putative nuclease-sensitive control element in unfertilized eggs of the sea urchin Lytechinus pictus.

Very limited nuclease-treatment of actively translating lysates from unfertilized eggs of the sea urchin Lytechinus pictus results in activation of the lysate. This activation is reflected by the ability of the nuclease-treated (or 'nuclease-activated') lysates to more efficiently utilize exogenous added RNAs. The activation may be reversed by adding small aliquots of untreated lysate to the nuclease-activated lysates. These results suggest that a nuclease-sensitive negative control element may be involved in the translational repression of unfertilized eggs, and that a deactivation of this control element is partially responsible for the dramatic activation of protein synthesis following fertilization in sea urchin eggs.

Translational initiation factors from sea urchin eggs and embryos: functional properties are highly conserved.

We have used three mammalian in vitro assays for translational initiation (globin synthesis, methionyl-puromycin synthesis, and ternary complex formation), consisting of defined components, to ask whether sea urchin (Strongylocentrotus purpuratus) egg and embryo translational components are active in heterologous assays for mammalian components, and to determine to what extent these activities are evolutionarily conserved. A "pH 5 enzyme" fraction prepared from unfertilized eggs and embryos efficiently replaced the rat liver pH 5 fraction in a globin synthesis assay, indicating that the elongation and termination factors and the aminoacyl-tRNAs are compatible with the mammalian translational machinery. The classical schemes for mammalian initiation factor purification yielded low or no detectable activities in the ribosomal salt washes, so a novel procedure was developed to partially purify initiation factors from sea urchin eggs and embryos before testing for activity. A 12,000 g homogenate from unfertilized eggs was fractionated by step elution from phosphocellulose at 100, 300, 600, and 1,200 mM salt. Initiation factor activities were found in each salt step as predicted for the mammalian counterparts. The following activities have been detected: eIF2, eIF3/4F, eIF4A, eIF4B, eIF4C, eIF4D, and eIF5. Further fractionation of each elution step yielded preparations enriched in specific initiation factor activities. However, denaturing polyacrylamide gel electrophoresis of the fractions gave complex polypeptide patterns and no clearly identifiable bands corresponding to the mammalian initiation factor polypeptides. In spite of the conservation of factor activity, crude and affinity purified polyclonal antibodies to the mammalian factors did not cross-react with the sea urchin preparations. The demonstration that initiation factor activities are sufficiently conserved to allow their being assayed is the first step in our dissection of the translational machinery of eggs and embryos, and in the complete analysis of the regulation of translation during early development.

Sperm-specific surface antigenicity common to seven animal phyla.

While studying the plasma membrane of sperm of the sea urchin Strongylocentrotus purpuratus, we developed an antiserum that exhibits unusual reactivity--it cross-reacts with the surfaces of spermatozoa of 28 species representing seven phyla of the animal kingdom. A negative cross-reaction has not been found. This suggests the possible existence of common antigenic determinants on the surface of all animal sperm. We report these preliminary results here because of the broad implications common sperm-surface antigenicity has for the potential development of immunocontraceptive methods.