Astronomical time-of-flight photon speedometer.

A dual-band, fiber-optic, photon time-of-flight instrument was developed. Its design was optimized for measuring the velocity of visible photons emanating from relatively dim astronomical sources (apparent magnitude m>12), such as distant galaxies and quasars. We report the first direct photon group velocity measurements for extragalactic objects. The photon group velocity is found to be 3.00±0.03×108 ms-1 and is invariant, within experimental error, over the range of redshifts measured (0≤z≤1.33). This measurement provides additional validation of general relativity and is consistent with the Friedmann-Lemaître-Robertson-Walker and hyperbolic anti-de Sitter metrics but not with the elliptical de Sitter metric.

Tumor-specific proteolytic processing of cyclin E generates hyperactive lower-molecular-weight forms.

Cyclin E is a G(1) cyclin essential for S-phase entry and has a profound role in oncogenesis. Previously this laboratory found that cyclin E is overexpressed and present in lower-molecular-weight (LMW) isoforms in breast cancer cells and tumor tissues compared to normal cells and tissues. Such alteration of cyclin E is linked to poor patient outcome. Here we report that the LMW forms of cyclin E are hyperactive biochemically and they can more readily induce G(1)-to-S progression in transfected normal cells than the full-length form of the protein can. Through biochemical and mutational analyses we have identified two proteolytically sensitive sites in the amino terminus of human cyclin E that are cleaved to generate the LMW isoforms found in tumor cells. Not only are the LMW forms of cyclin E functional, as they phosphorylate substrates such as histone H1 and GST-Rb, but also their activities are higher than the full-length cyclin E. These nuclear localized LMW forms of cyclin E are also biologically functional, as their overexpression in normal cells increases the ability of these cells to enter S and G(2)/M. Lastly, we show that cyclin E is selectively cleaved in vitro by the elastase class of serine proteases to generate LMW forms similar to those observed in tumor cells. These studies suggest that the defective entry into and exit from S phase by tumor cells is in part due to the proteolytic processing of cyclin E, which generates hyperactive LMW isoforms whose activities have been modified from that of the full-length protein.

Processing of cyclin E differs between normal and tumor breast cells.

Cyclin E is a G1 cyclin essential for G1 to S-phase transition of the cell cycle with a profound role in oncogenesis. In tumor cells and tissues, cyclin E is overexpressed and present in its lower molecular weight (LMW) isoforms, and it can be used as a prognosticator for poor patient outcome. In this study, we have examined differences in the processing of cyclin E between normal mammary epithelial and breast cancer cell lines. Five NH2-terminally deleted epitope-tagged (FLAG) cyclin E vectors were constructed spanning the range of LMW forms observed in tumor cells. These constructs were transfected into normal and tumor cells and analyzed for the production of cyclin E-FLAG protein products by Western blot analysis with FLAG and cyclin E antibodies. Our results show that only tumor cells had the machinery to process these cyclin E-FLAG constructs to their LMW forms, whereas normal cells mainly expressed the full-length unprocessed form of each protein. Tumor and normal cells always process the cyclin E-FLAG protein in the same way as endogenously expressed cyclin E. This phenomenon is consistent with all of the cell lines used, regardless of transfection efficiency, time of processing posttransfection, or method of transfection. Furthermore, measurement of FLAG-associated kinase activity in the transfectants revealed that the protein products of the cyclin E-FLAG constructs are 10 times more active in tumor cells than in normal cells. These studies suggest that the LMW forms of cyclin E detected at a much higher level in tumor cells arise from posttranslational action of a protease.

Physiologic tremor and microsurgery.

Physiologic tremor hampers the ability of students to learn microsurgical technique. An understanding of normal tremor both as to origin and methods of control would be of help. Physiological tremor arises from both mechanical and neuromuscular sources and is made worse by a number of factors. The "size principle of motoneuron recruitment" is an important physiologic consideration, and the use of biofeedback techniques enables the student to confirm his understanding of the principle. Knowledge of the factors which aggravate physiological tremor allows the microsurgeon to control his own tremor both in the laboratory and in the operating room.