LEAFY COTYLEDON2 encodes a B3 domain transcription factor that induces embryo development.

The Arabidopsis LEAFY COTYLEDON2 (LEC2) gene is a central embryonic regulator that serves critical roles both early and late during embryo development. LEC2 is required for the maintenance of suspensor morphology, specification of cotyledon identity, progression through the maturation phase, and suppression of premature germination. We cloned the LEC2 gene on the basis of its chromosomal position and showed that the predicted polypeptide contains a B3 domain, a DNA-binding motif unique to plants that is characteristic of several transcription factors. We showed that LEC2 RNA accumulates primarily during seed development, consistent with our finding that LEC2 shares greatest similarity with the B3 domain transcription factors that act primarily in developing seeds, VIVIPAROUS1/ABA INSENSITIVE3 and FUSCA3. Ectopic, postembryonic expression of LEC2 in transgenic plants induces the formation of somatic embryos and other organ-like structures and often confers embryonic characteristics to seedlings. Together, these results suggest that LEC2 is a transcriptional regulator that establishes a cellular environment sufficient to initiate embryo development.

Expression of the S receptor kinase in self-compatible Brassica napus cv. Westar leads to the allele-specific rejection of self-incompatible Brassica napus pollen.

Expression of an S receptor kinase (SRK910) transgene in the self-compatible Brassica napus cv. Westar conferred on the transgenic pistil the ability to reject pollen from the self-incompatible Brassica napus W1 line, which carries the S910 allele. In one of the SRK transgenic lines, 1C, virtually no seeds were produced when the transgenic pistils were pollinated with W1 pollen (Mean number of seeds per pod = 1.22). This response was specific to the W1 pollen since pollen from a different self-incompatible Brassica napus line (T2) and self-pollinations were fully compatible. Westar plants expressing an S locus glycoprotein transgene (SLG910) did not show any self-incompatibility response towards W1 pollen. Transgenic Westar plants resulting from crosses between the 1C SRK transgenic line and three SLG910 transgenic lines were also tested for rejection of W1 pollen. The additional expression of the SLG910 transgene in the SRK910 transgenic plants did not cause any significant further reduction in seed production (Mean seeds/pod = 1.04) or have any detectable effects on the number of pollen grains that adhered to the pistil. Thus, while the allele-specific SLG gene was previously reported to have an enhancing effect on the self-incompatibility response, no evidence for such a role was found in this study.

A breakdown of Brassica self-incompatibility in ARC1 antisense transgenic plants.

Self-incompatibility, the rejection of self pollen, is the most widespread mechanism by which flowering plants prevent inbreeding. In Brassica, the S receptor kinase (SRK) has been implicated in the self-incompatibility response, but the molecular mechanisms involving SRK are unknown. One putative downstream effector for SRK is ARC1, a protein that binds to the SRK kinase domain. Here it is shown that suppression of ARC1 messenger RNA levels in the self-incompatible Brassica napus W1 line is correlated with a partial breakdown of self-incompatibility, resulting in seed production. This provides strong evidence that ARC1 is a positive effector of the Brassica self-incompatibility response.

Comparing ambulatory preceptors' and students' perceptions of educational planning.

To compare ambulatory preceptors' and students' perceptions of the use of educational planning (setting goals, assessing needs, formulating objectives, choosing methods, and providing feedback and evaluation) in the office setting, we mailed a survey, which was returned by 127 longitudinal ambulatory preceptors and 168 first-year and second-year medical students. Faculty perceptions did not match student perceptions of what occurred in the longitudinal preceptor program teaching sessions in educational planning areas. Students perceived these activities were occurring with much less frequency than faculty perceived. Medical education needs to move beyond the usual faculty development workshop paradigm to a more comprehensive educational development model that includes training both faculty and students in core educational skills. This will enable the ambulatory setting to reach its full educational potential in training future physicians.

Faculty development for community-based physicians at the University of Massachusetts and SUNY-Buffalo.

Community-based faculty development (CBFD) is becoming increasingly important as medical education moves into the ambulatory/office-based setting CBFD provides preceptors with essential knowledge, skills, and attitudes directly related to teaching while providing a sense of identity as teachers to a diverse group of practitioners in a variety of settings. This article reviews the structure and function of successful community-based faculty development, using as examples programs from the University of Massachusetts Medical School and the State University of New York at Buffalo that were supported by The Robert Wood Johnson Foundation's Generalist Physician Initiative. After reviewing the literature on successful implementation of programs dedicated to community-based precepting, the authors investigate the educational concepts, instructional designs, and operational characteristics that are the framework for providing successful faculty development to community-based preceptors. They list rationales and examples of the educational methods used and compare structural components of the programs at both institutions. Last, they explore future directions in the rapidly changing medical education environment that need to be addressed in CBFD in the areas of outcome/program evaluation, comprehensive needs assessment, and regionalization.

Course-based assessment: implementing outcome assessment in medical education.

Rapid, intensive change in the health care system requires a change in how the outcomes of medical education are measured. The post-Flexner model of evaluating the institution focuses on teaching (rather than learning) and is not relevant to ambulatory training. Medical education needs to use assessment that focuses on student learning, can respond quickly to changes, and is continuously refined by use of information about students' abilities. Course-based assessment is a systematic way to gather, analyze, disseminate, and use course data to improve student learning, and it is well suited to current trends in health professions education. The authors present and discuss six principles of effective outcome assessment in medical education and illustrate these principles from their experience of using this type of assessment in a pre-clinical course integrating basic science, social science, and clinical skills. Courses and programs for medical students and residents should use course-based assessment to ensure that medical trainees acquire the skills and attitudes needed to practice medicine well. The next challenge for medical educators is to implement course-based assessment that is intimately tied to a broader institutional plan.

White noise analysis of a chromatic type horizontal cell in the Xenopus retina.

The dynamics of color-coded signal transmission in the light-adapted Xenopus retina were studied by a combination of white noise (Wiener) analysis and simultaneous recordings from two types of horizontal cells: chromatic-type horizontal cells (C-HCs) are hyperpolarized by blue light and depolarized by red light, whereas luminosity-type horizontal cells (L-HCs) are hyperpolarized by all wave-lengths. The retina was stimulated by two superimposed fields of red and blue light modulated by two independent white noise signals, and the resulting intracellular responses were decomposed into red and blue components (first-order kernels). The first-order kernels predict the intracellular responses with a small degree of error (3.5-9.5% in terms of mean square error) under conditions where modulated responses exceeded 30 mV in amplitude peak-to-peak, thus demonstrating that both red and blue modulation responses are linear. Moreover, there is little or no interaction between the red- and blue-evoked responses; i.e., nearly identical first-order kernels were obtained for one color whether the other color was modulated or not. In C-HCs (but not L-HCs), there were consistent differences in the dynamics of the red and blue responses. In the C-HC, the cutoff frequency of the red response was higher than for the blue (approximately 12 vs 5 Hz), and the red kernel was more bandpass than the blue. In the L-HC, kernel waveform and cutoff frequencies were similar for both colors (approximately 12 Hz or greater), and the time-to-peak of the L-HC kernel was always shorter than either the red or blue C-HC kernel. These results have implications for the mechanisms underlying color coding in the distal retina, and they further suggest that nonlinear phenomena, such as voltage-dependent conductances in HCs, do not contribute to the generation of modulation responses under the experimental conditions used here.

Attitudes of adolescents toward smoking cessation.

We surveyed 375 10th grade students on present behaviors regarding cigarette use and on attitudes concerning smoking cessation. Fourteen percent of students were daily smokers and 7% were occasional smokers. Of the daily smokers, 28% said their most important reason for continued smoking was because they were addicted, and 52% reported two or more prior cessation attempts. When asked the most important reasons for wanting to quit, 70% of occasional smokers and 43% of daily smokers listed health as the most important concern. Only daily smokers (22%) wanted to quit because they thought they were addicted. We conclude that daily smokers among adolescents have many characteristics of adult smokers and that intervention efforts among adolescent smokers may need to be tailored differently for such "adult pattern" smokers as compared to occasional smokers, particularly in regard to addressing the question of smoking as an addictive behavior.

Presumptive evidence for Blastocystis hominis as a cause of colitis.

A patient with persistent diarrhea was found to have biopsy-proved colitis with large numbers of the protozoan Blastocystis hominis present in stool. Extensive evaluation failed to reveal any other potential etiologic agent of acute colitis. Following treatment with a course of metronidazole, the patient became asymptomatic, B hominis was no longer present in stool, and results of a repeated biopsy were normal. These observations are consistent with the role of B hominis as a gastrointestinal pathogen.

Area postrema lesions block feeding induced by systemic injections of monosodium glutamate.

Glutamate is an amino acid neurotransmitter capable of producing widespread receptor-mediated neuronal excitation. Recently we reported that high doses of monosodium glutamate (MSG) given systemically stimulate food intake in a dose-related fashion. Since glutamate does not cross the blood-brain barrier, it seems possible that feeding was stimulated by an action of glutamate on neurons within circumventricular organs (CVOs), areas of the brain in which the blood-brain barrier is deficient. In this experiment, we tested the hypothesis that systemic MSG stimulates feeding by an action on the area postrema (AP), a CVO in the caudal hindbrain. AP-lesioned rats (APLs) and sham-operated controls (shams) were injected with saline or MSG (2 and 6 g/kg, SC, one dose per week). Food intake was measured for 3 hr immediately following the injection. Shams increased their food intake significantly in response to both doses of MSG, but APLs did not. This result suggests that systemic glutamate may stimulate feeding by an action on the AP.

Glucagon-induced inhibition of feeding is impaired by hepatic portal alloxan injection.

Subdiabetogenic doses of alloxan injected into the hepatic portal vein of rats abolished glucagon-induced inhibition of feeding (glucagon satiety) both in daytime tests using a palatable food and in nighttime tests using their standard pelleted diet. In contrast, inhibition of food intake by cholecystokinin and epinephrine and stimulation of feeding by 2-deoxy-D-glucose were not impaired by alloxan. Alloxan-induced deficits in glucagon satiety did not appear to result from generalized hepatocellular necrosis, because satiety deficits outlasted histological signs of toxicity and because furosemide, which produced a similar degree of hepatotoxicity, did not impair glucagon satiety. In addition, alloxan's effects were not associated with impaired glycogen storage or mobilization. Recovery of glucagon satiety occurred in some animals but not until 3-6 mo after alloxan. The degree of recovery was inversely related to alloxan dose. Our results indicate that, when administered into the hepatic portal vein, alloxan may be a relatively specific toxin for cells involved in the mediation of glucagon satiety. The specificity of the deficit and the time course of recovery suggest that the alloxan-sensitive cells may be hepatic vagal neurons.

Synaptic feedback onto photoreceptors in the ocellar retina.

Intracellular studies from photoreceptors and second order neurons in the dragonfly ocellar retina suggest that the hyperpolarizing OFF oscillation in the photoreceptor reflects synaptic feedback from second order neurons onto receptor terminals. The receptor OFF response was normally observed when recording more proximally, closer to the nuclear and synaptic region, but it was not seen when recording more distally, closer to the rhabdomeric end of the cell. Both the hyperpolarizing OFF response in the receptor and the depolarizing OFF response in the second order cell are apparently generated in the ocellar plexiform layer because they were not eliminated when the second order processes were isolated from the brain. In both intact and cut nerve preparations, the receptor OFF response was blocked by curare and enhanced by picrotoxin, the same drugs that were reported to selectively modify the response of the second order cell. In addition, a normal-appearing OFF response was recorded intracellularly from the dark-adapted photoreceptor in response to the application of brief hyperpolarizing current pulses to the ocellar nerve. These results support a model of sign-conserving feedback from second order neurons onto receptor terminals and are consistent with the hypothesis that the receptor transmitter may be acetylcholine and the feedback transmitter could be GABA.

Porcine granulosa and cumulus cell properties. LH/hCG receptors, ability to secrete progesterone and ability to respond to LH.

In order to compare the properties of isolated cumulus and granulosa cells, granulosa cells and cumulus cells surrounding oocytes were harvested from small (1-2 mm), medium (3-5 mm) and large (6-12 mm) porcine antral follicles and the number of LH/hCG receptors was measured by the binding of [125I]hCG. The ability of the cells to secrete progesterone in culture was examined in the presence and absence of hCG and LH. In 3 separate experiments of 1-h incubations at 37 degrees C using cells harvested from medium-sized follicles, granulosa cells bound 10--15-fold more iodinated hCG than an equivalent number of cumulus cells. During a 2-day culture period, cumulus cells secreted less progesterone than granulosa cells from medium- and large-sized antral follicles (p less than 0.01). The potential of both cumulus and granulosa cells to secrete progesterone in culture increased as the follicle progressed from small to large size. Also, the ability of the oocyte to mature in culture increased with antral follicle size. Concurrently the ability of cumulus-oocyte complexes to form monolayers in culture decreased as the follicle matured. Cumulus and granulosa cells harvested from small- and medium-sized follicles responded similarly to LH and hCG with a stimulation in progesterone secretion after 2-6 days in culture.

A stimulatory effect of the fluid from preimplantation rabbit blastocysts upon luteinization of monkey granulosa cell cultures.

Blastocyst fluid was aspirated from Day 6 1/2--7 rabbit blastocysts and was added to cultures of granulosa cells obtained from preovulatory follicles of untreated rhesus monkeys or from follicles of monkeys or from follicles of monkeys treated with PMSG. The stimulation of progesterone secretion was measured and equated with that produced by hCG. The hCG-like activity was also measured in a radioreceptor assay using 125I-labelled hCG and porcine granulosa cells. In 8 out of 10 experiments with cultured cells from untreated monkeys, addition of 20% blastocyst fluid from Days 6--9 of culture stimulated progesterone secretion by 2- to 6-fold. Similar findings were obtained in 5 experiments with cultures from PMSG-treated monkeys except that the blastocyst fluid was added from Days 0 to 6 of culture. The granulosa cells in such cultures underwent morphological luteinization. Compared to a standard of purified hCG the blastocyst fluid contained about 0.76--2.5 ng hCG-like activity/ml which was non-dialysable. The radioreceptor assay indicated the presence of 0.5--2.5 ng hCG-like material/ml.