Space construction system analysis. Part 2: Construction analysis

The construction methods specific to the end to end construction process for building the ETVP in low Earth orbit, using the space shuttle orbiter as a construction base, are analyzed. The analyses concerned three missions required to build the basic platform. The first mission involved performing the fabrication of beams in space and assembling the beams into a basic structural framework. The second mission was to install the forward support structure and aft support structure, the forward assembly, and a TT&C antenna. The third mission plan was to complete the construction of the platform and activate it to begin operations in low Earth orbit. The integration of the activities for each mission is described along with the construction requirements and construction logic

Expression of a dominant negative inhibitor of intercellular communication in the early Xenopus embryo causes delamination and extrusion of cells

A chimeric construct, termed 3243H7, composed of fused portions of the rat gap junction proteins connexin32 (Cx32) and connexin43 (Cx43) has been shown to have selective dominant inhibitory activity when tested in the Xenopus oocyte pair system. Co-injection of mRNA coding for 3243H7 together with mRNAs coding for Cx32 or Cx43 completely blocked the development of channel conductances, while the construct was ineffective at blocking intercellular channel assembly when coinjected with rat connexin37 (Cx37). Injection of 3243H7 into the right anterodorsal blastomere of 8-cell-stage Xenopus embryos resulted in disadhesion and delamination of the resultant clone of cells evident by embryonic stage 8; a substantial number, although not all, of the progeny of the injected cell were eliminated from the embryo by stage 12. A second construct, 3243H8, differing from 3243H7 in the relative position of the middle splice, had no dominant negative activity in the oocyte pair assay, nor any detectable effects on Xenopus development, even when injected at four-fold higher concentrations. The 3243H7-induced embryonic defects could be rescued by coinjection of Cx37 with 3243H7. A blastomere reaggregation assay was used to demonstrate that a depression of dye-transfer could be detected in 3243H7-injected cells as early as stage 7; Lucifer yellow injections into single cells also demonstrated that injection of 3243H7 resulted in a block of intercellular communication. These experiments indicate that maintenance of embryonic cell adhesion with concomitant positional information requires gap junction-mediated intercellular communication.link_to_subscribed_fulltex

Connexin40, a component of gap junctions in vascular endothelium, is restricted in its ability to interact with other connexins.

The cellular distribution of connexin40 (Cx40), a newly cloned gap junction structural protein, was examined by immunofluorescence microscopy using two different specific anti-peptide antibodies. Cx40 was detected in the endothelium of muscular as well as elastic arteries in a punctate pattern consistent with the known distribution of gap junctions. However, it was not detected in other cells of the vascular wall. By contrast, Cx43, another connexin present in the cardiovascular system, was not detected in endothelial cells of muscular arteries but was abundant in the myocardium and aortic smooth muscle. We have tested the ability of these connexins to interact functionally. Cx40 was functionally expressed in pairs of Xenopus oocytes and induced the formation of intercellular channels with unique voltage dependence. Unexpectedly, communication did not occur when oocytes expressing Cx40 were paired with those expressing Cx43, although each could interact with a different connexin, Cx37, to form gap junction channels in paired oocytes. These findings indicate that establishment of intercellular communication can be spatially regulated by the selective expression of different connexins and suggest a mechanism that may operate to control the extent of communication between cells

Over-expression of FoxM1 stimulates cyclin B1 expression

FoxM1 (previously named WIN, HFH-11 or Trident) is a Forkhead box (Fox) transcription factor widely expressed in proliferating cells. Various findings, including a recent analysis of FoxM1 knockout mice, suggest that FoxM1 is required for normal S-M coupling during cell cycle progression. To study the regulatory role of FoxM1 and its downstream regulatory targets, three stably transfected HeLa lines that display doxycycline (dox)-inducible FoxM1 expression were established. Over-expression of FoxM1 by dox induction facilitates growth recovery from serum starvation. Quantitation of cyclin B1 and D1 levels using flow cytometric, Western and Northern analyses reveals that elevated FoxM1 levels lead to stimulation of cyclin B1 but not cyclin D1 expression. Transient reporter assays in the dox-inducible lines and upon co-transfection with a constitutive FoxM1 expression plasmid suggest that FoxM1 can activate the cyclin B1 promoter. © 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.link_to_subscribed_fulltex