Setting the pace: host rhythmic behaviour and gene expression patterns in the facultatively symbiotic cnidarian Aiptasia are determined largely by Symbiodinium

BACKGROUND

All organisms employ biological clocks to anticipate physical changes in the environment; however, the integration of biological clocks in symbiotic systems has received limited attention. In corals, the interpretation of rhythmic behaviours is complicated by the daily oscillations in tissue oxygen tension resulting from the photosynthetic and respiratory activities of the associated algal endosymbiont Symbiodinium. In order to better understand the integration of biological clocks in cnidarian hosts of Symbiodinium, daily rhythms of behaviour and gene expression were studied in symbiotic and aposymbiotic morphs of the sea-anemone Aiptasia diaphana.

RESULTS

The results showed that whereas circatidal (approx. 12-h) cycles of activity and gene expression predominated in aposymbiotic morphs, circadian (approx. 24-h) patterns were the more common in symbiotic morphs, where the expression of a significant number of genes shifted from a 12- to 24-h rhythm. The behavioural experiments on symbiotic A. diaphana displayed diel (24-h) rhythmicity in body and tentacle contraction under the light/dark cycles, whereas aposymbiotic morphs showed approximately 12-h (circatidal) rhythmicity. Reinfection experiments represent an important step in understanding the hierarchy of endogenous clocks in symbiotic associations, where the aposymbiotic Aiptasia morphs returned to a 24-h behavioural rhythm after repopulation with algae.

CONCLUSION

Whilst some modification of host metabolism is to be expected, the extent to which the presence of the algae modified host endogenous behavioural and transcriptional rhythms implies that it is the symbionts that influence the pace. Our results clearly demonstrate the importance of the endosymbiotic algae in determining the timing and the duration of the extension and contraction of the body and tentacles and temporal gene expression.

Photosynthetic circadian rhythmicity patterns of Symbiodinium, [corrected] the coral endosymbiotic algae

Biological clocks are self-sustained endogenous timers that enable organisms (from cyanobacteria to humans) to anticipate daily environmental rhythms, and adjust their physiology and behaviour accordingly. Symbiotic corals play a central role in the creation of biologically rich ecosystems based on mutualistic symbioses between the invertebrate coral and dinoflagellate protists from the genus Symbiodinium. In this study, we experimentally establish that Symbiodinium photosynthesis, both as a free-living unicellular algae and as part of the symbiotic association with the coral Stylophora pistillata, is ‘wired’ to the circadian clock mechanism with a ‘free-run’ cycle close to 24 h. Associated photosynthetic pigments also showed rhythmicity under light/dark conditions and under constant light conditions, while the expression of the oxygen-evolving enhancer 1 gene (within photosystem II) coincided with photosynthetically evolved oxygen in Symbiodinium cultures. Thus, circadian regulation of the Symbiodinium photosynthesis is, however, complicated as being linked to the coral/host that have probably profound physiochemical influence on the intracellular environment. The temporal patterns of photosynthesis demonstrated here highlight the physiological complexity and interdependence of the algae circadian clock associated in this symbiosis and the plasticity of algae regulatory mechanisms downstream of the circadian clock.

The effect of temperature compensation on the circadian rhythmicity of photosynthesis in Symbiodinium, coral-symbiotic alga

Circadian rhythms, which are found in most eukaryotes, are defined as rhythms that persist under constant conditions with a periodicity close to 24 h. One central key characteristic of all circadian rhythms is “temperature compensation”, which allows organisms to maintain robust rhythms with a period close to a diel cycle over a broad range of physiological temperatures. To better understand the response of the circadian clock in corals to temperature elevation, photosynthesis as an output process of the circadian clock was studied both in Stylophora pistillata corals and in cultured Symbiodinium algae. The time period of photosynthesis was not affected by temperature elevation in the cultured algae or in the corals harbouring Symbiodinium. However, the photosynthetic system responded to temperature elevations by adjusting the photosynthetic apparatus. These findings suggest that the endogenous algal circadian clock regulates the photosynthetic rhythm and compensates for temperature elevations that occur in the natural environment.

Family physicians' initiative to increase compliance with screening mammography--an innovative community project

BACKGROUND

Breast cancer is the most common malignancy among women in Israel and throughout the world. Israeli women aged 50-75 years are advised to undergo a mammographic screening examination every 2 years. However, the lack of a structured referral system is reflected in the low utilization rate of mammography.

OBJECTIVES

To describe an innovative program in which family physicians in an urban clinic developed a model framework for referrals, coordinated with radiologists and surgeons, aimed at increasing compliance among women referred for mammography.

METHODS

A community-based study was conducted, outside of the regular reception hours, in a neighborhood practice with a population of 527 women aged 50-75. A referral system under the supervision of family physicians was designed, and the women received appointments for mammography at specified days and hours. The results of the examination were sent to the physician who used dedicated time to continue the diagnostic and/or therapeutic process, as appropriate. At the physician's instructions a research assistant contacted the women who did not keep their appointments, and scheduled a second appointment.

RESULTS

In 1993, the year prior to the study, when women referred themselves for mammography, the utilization rate was 9%. During the study year the utilization rate was 77%. Women born in Europe or America had higher compliance rates than women born in Asia or Africa (81% vs. 72%, respectively). Married women were more compliant than unmarried women (81% vs. 70%, respectively). No correlation was found between compliance and age, family history of cancer in general, or breast cancer in particular. Six new cases of breast cancer were detected.

CONCLUSIONS

The initiative of family physicians increased the utilization of mammography among women under their care. Family physicians allocated time outside of their regular reception hours for the program. A relatively large number of new malignancies were found, but this impression should be confirmed or negated by a large-scale study using the same methods.

Gallium scanning in differentiating malignant from benign asbestos-related pleural disease

In order to assess the utility of 67gallium citrate in delineating malignant pleural mesothelioma from benign asbestos-related pleural disease, 49 patients with malignant mesothelioma and 16 with benign asbestos-related pleural disease were studied. Seven patients with malignant mesothelioma had no history of asbestos exposure, while the remaining 58 patients were exposed. Forty-three of the 49 patients (88%) with malignant mesothelioma had a positive 67gallium scan including 36 of the 42 (86%) patients with asbestos exposure and all 7 patients without a history of asbestos exposure. Three of 16 patients (19%) with benign asbestos-related pleural disease had a positive scan. 67Gallium radionuclide imaging is nonspecific but may be valuable in noninvasive monitoring of asbestos-exposed populations, which have a high risk for the late development of benign and/or malignant pleural disease.

Cisternography and CT scanning with 111In-DTPA in evaluation of posterior fossa arachnoid cysts

A patient with a large, long-standing posterior fossa arachnoid cyst was evaluated. Computed tomography was used to demonstrate the cyst. 1111In-DTPA cisternography demonstrated the communication of the cyst with the subarachnoid space, stasis of the 111In in the cystic space, and incomplete ascent of cerebrospinal fluid over the cerebral hemispheres.