Tricellulin forms homomeric and heteromeric tight junctional complexes

Sealing of the paracellular cleft by tight junctions is of central importance for epithelia and endothelia to function as efficient barriers between the extracellular space and the inner milieu. Occludin and claudins represent the major tight junction components involved in establishing this barrier function. A special situation emerges at sites where three cells join together. Tricellulin, a recently identified tetraspan protein concentrated at tricellular contacts, was reported to organize tricellular as well as bicellular tight junctions. Here we show that in MDCK cells, the tricellulin C-terminus is important for the basolateral translocation of tricellulin, whereas the N-terminal domain appears to be involved in directing tricellulin to tricellular contacts. In this respect, identification of homomeric tricellulin-tricellulin and of heteromeric tricellulin-occludin complexes extends a previously published model and suggests that tricellulin and occludin are transported together to the edges of elongating bicellular junctions and get separated when tricellular contacts are formed.     

Weighted LBF for spaceborne general bistatic SAR processing

Loffeld＇s bistatic formula （LBF） is the first two-dimensional analytic point target reference spectrum derived for general bistatic SAR frequency domain focusing. The phase history is expanded in Taylor series around the individual points of stationary phase of the trans- mitter-target and target-receiver phase histories, respectively, and thus the common bistatic stationary phase point can be obtained using the method of stationary phase. Unfortunately, it shows limitations for extreme bistatic configurations, namely the highly squinted mode and space-surface application. The weighted LBF （WLBF） is proposed in this paper based on the different contributions of total phase modulation from the transmitter and receiver. The formulae we derived are compared with that of the original literature. The extreme bistatic stripmap SAR data can be focused using WLBF, which accommodates the spaceborne squint geometry using the modified effective velocity solution. A point target simulation example is presented to verify the accuracy of the new WLBF spectrum.     

Transcriptional regulation of a metastasis suppressor gene by Tip60 and beta-catenin complexes

Defining the molecular strategies that integrate diverse signalling pathways in the expression of specific gene programmes that are critical in homeostasis and disease remains a central issue in biology. This is particularly pertinent in cancer biology because downregulation of tumour metastasis suppressor genes is a common occurrence, and the underlying molecular mechanisms are not well established. Here we report that the downregulation of a metastasis suppressor gene, KAI1, in prostate cancer cells involves the inhibitory actions of beta-catenin, along with a reptin chromatin remodelling complex. This inhibitory function of beta-catenin-reptin requires both increased beta-catenin expression and recruitment of histone deacetylase activity. The coordinated actions of beta-catenin-reptin components that mediate the repressive state serve to antagonize a Tip60 coactivator complex that is required for activation; the balance of these opposing complexes controls the expression of KAI1 and metastatic potential. The molecular mechanisms underlying the antagonistic regulation of beta-catenin-reptin and the Tip60 coactivator complexes for the metastasis suppressor gene, KAI1, are likely to be prototypic of a selective downregulation strategy for many genes, including a subset of NF-kappaB target genes.