Function of the Drosophila TGF-alpha homolog Spitz is controlled by Star and interacts directly with Star.

Drosophila Spitz is a homolog of transforming growth factor alpha (TGF-alpha) and is an activating ligand for the EGF receptor (Egfr). It has been shown that Star is required for Spitz activity. Here we show that Star is quantitatively limiting for Spitz production during eye development. We also show that Star and Spitz proteins colocalize in Spitz sending cells and that this association is not coincident with the site of translation--consistent with a function for Star in Spitz processing or transmission. Finally, we have defined minimal sequences within both Spitz and Star that mediate a direct interaction and show that this binding can occur in vivo.

Role of the EGF receptor pathway in growth and patterning of the Drosophila wing through the regulation of vestigial.

Growth and patterning of the Drosophila wing disc depends on the coordinated expression of the key regulatory gene vestigial both in the Dorsal-Ventral (D/V) boundary cells and in the wing pouch. We propose that a short-range signal originating from the core of the D/V boundary cells is responsible for activating EGFR in a zone of organizing cells on the edges of the D/V boundary. Using loss-of-function mutations and ectopic expression studies, we show that EGFR signaling is essential for vestigial transcription in these cells and for making them competent to undergo subsequent vestigial-mediated proliferation within the wing pouch.

The role of star in the production of an activated ligand for the EGF receptor signaling pathway.

The Star gene is a member of the EGFR signaling pathway which has diverse functions throughout Drosophila development. In order to investigate the protein distribution for Star, we have generated a polyclonal antibody. Here, we show that the Star protein is expressed perinuclearly in the early female germline and later is found in the oocyte cytoplasm. Star is expressed at low levels in other tissues. The subcellular localization of the protein has been determined when Star is overexpressed in the eye disc. Star is located in the nuclear and contiguous endoplasmic reticulum membranes. A functional assay in the wing disc demonstrates that Star expression can activate a nonprocessed membrane-bound form of the EGFR ligand Spitz and overexpression of Star in the eye disc promotes the formation of smaller Spitz proteins. Based on these results, we propose that the Star protein is likely to be involved in Spitz ligand processing.

Characterization of Star and its interactions with sevenless and EGF receptor during photoreceptor cell development in Drosophila.

Loss-of-function mutations in Star impart a dominant rough eye phenotype and, when homozygous, are embryonic lethal with ventrolateral cuticular defects. We have cloned the Star gene and show that it encodes a novel protein with a putative transmembrane domain. Star transcript is expressed in a dynamic pattern in the embryo including in cells of the ventral midline. In the larval eye disc, Star is expressed first at the morphogenetic furrow, then in the developing R2, R5, and R8 cells as well as in the posterior clusters of the disc in additional R cells. Star interacts with Drosophila EGF receptor in the eye and mosaic analysis of Star in the larval eye disc reveals that homozygous Star patches contain no developing R cells. Taken together with the expression pattern at the morphogenetic furrow, these results demonstrate an early role for Star in photoreceptor development. Additionally, loss-of-function mutations in Star act as suppressors of R7 development in a sensitized genetic background involving the Son of sevenless (Sos) locus, and overexpression of Star enhances R7 development in this genetic background. Based on the genetic interactions with Sos, we suggest that Star also has a later role in photoreceptor development including the recruitment of the R7 cell through the sevenless pathway.

Obstacles to continuing education.

An earlier study showed that low attendance at section 63 courses of continuing education was not explained by dissatisfaction with content or methods employed in these programmes. In this enquiry to the same sample of 105 general practitioners, several additional factors were studied related to enjoyment of professional role, practice skills and perceived obstacles to continuing education. Thirty-seven per cent of respondents said that their work was less than fully enjoyable and one in 20 found no enjoyment; similarly, 30 per cent were dissatisfied with their organizational skills but for neither of these factors was there any difference between attenders and non-attenders. Half of the sample found difficulty in keeping up to date, and in this finding the proportion who were attenders was significantly higher than non-attenders. Eighty-two per cent had encountered obstacles to their continuing education, in particular lack of time, practice commitments and the need to preserve family life. Recommendations for an ideal system of continuing education included high acceptance of self-assessment exercises as a means of identifying areas of educational need.

The general practitioner and continuing education.

Concern that the existing provision for organized continuing education was not matching the needs of general practitioners in either content or teaching method prompted this Nottinghamshire survey. An initial postal questionnaire elicited responses from 50 per cent of a sample of general practitioners in the county; the non-responding group was then followed up by use of an abbreviated questionnaire and interviews, with about 50 per cent success. The findings are derived from the main sample and from two subsamples of the non-responders.The findings from the survey have shown up the relative popularity of section 63 courses and, in addition, have revealed that two thirds of those doctors who did not attend section 63 courses had attended some other form of educational activity, which suggests that only a small number of general practitioners have poor motivation towards their own continuing education. The content on offer would appear to be in the most popular areas and the methods used the most acceptable. However, a low priority was accorded to research and audit techniques, and this is disturbing.

Comparison of the effect of amitriptyline in standard and sustained-release formulations on cardiac systolic time intervals.

Eight healthy male volunteers were given single doses of 75 mg standard and sustained-release amitriptyline in a double-blind, crossover trial. Systolic time intervals (STI) were measured hourly on drug and base-line days. Plasma amitriptyline and nortriptyline were measured hourly on drug days. To correct for diurnal variations, STI values on drug days were compared with values of base-line days at the same hour. Both formulations of amitriptyline produced initial decreases in heart rate (followed by a return to normal values) and a significant decrease in ventricular electrical systole (QTc), which began before plasma amitriptyline could be detected. One of the eight volunteers showed T wave depression following amitriptyline. The preejection period (PEPc) increased significantly in three of the eight volunteers (max 19%), and this change was due to an increase in true isovolumetric contraction time (TICT). The left ventricular ejection time (LVETc) decreased significantly in all volunteers (5%, p less than 0.001), the change being greater after sustained-release amitriptyline. Standard amitriptyline produced larger changes than sustained-release amitriptyline in QTc and PEPc. The overall increase in the PEP/LVET ratio, indicating an impairment of cardiac function, was twice as large after standard than after sustained-release amitriptyline (38% and 16%, respectively). The possible mechanisms of cardiac effects of amitriptyline are discussed. Our findings indicate that a sustained-release preparation may be safer than a standard preparation of amitriptyline, particularly if there is a risk of cardiac complications.