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The IL-6 receptor complex is expressed in different polarized epithelial cells such as liver hepatocytes and intestinal cells. It consists of two subunits: gp80, which binds the ligand, and gp130, which is responsible for signal transduction. In stably transfected Madin-Darby canine kidney (MDCK) cells we have studied the localization of the human IL-6 receptor subunits and found that gp80 and gp130 are predominantly expressed at the basolateral membrane. Analysis of MDCK cells expressing truncated forms of gp80 or gp130 showed that loss of the cytoplasmic domains results in apical delivery. Expression of deletion mutants of gp80 in MDCK cells led to the identification of two discontinous motifs responsible for basolateral sorting: a membrane-proximal tyrosine-based motif (YSLG) and a more membrane-distal dileucine-type motif (LI). Activation of signal transducer and activator of transcription-3 (STAT-3) only occurred via basolaterally located gp80, suggesting that endogenous gp130 is also constrained to the basolateral plasma membrane. Our identification of a basolateral sorting signal within the cytoplasmic region of gp80 for the first time attributes a function to this domain.

Diatom identification is a key step in using these microorganisms as water quality bioindicators. Morphological diagnosis is a difficult task due to the enormous number of species and their microscopic size. This can be overcome using molecular tools to complement the diagnosis. The main goal of this work was to obtain the DNA barcode of Ecuadorian epilithic diatoms with a wide geographical distribution, a well-defined ecological range and characteristics that allow them to be reliable indicator species. Unialgal diatom cultures were obtained from environmental samples of Ecuadorian Andean streams. Morphological characterization of cultures was carried out under SEM microscopy. For molecular characterization, 18SV4 and rbcL barcodes were sequenced from each strain and blasted against a GenBank database. A phylogenetic tree for each barcode was constructed using the ML method including sequences of strains of the studied species from different geographical locations. The results showed the following five species to be suitable as bioindicators and these were isolated. Sellaphora seminulum (strain JA01b, c), Nitzschia fonticola (strain SP02a) and N. palea (strain CA01a) are tolerant to eutrophication; Eolimna minima (strain CH02a) is a mesotrophic water bioindicator, and Achnanthidium minutissimum (strain JA01a) is an oligotrophic water bioindicator. The comparison with the GenBank database of the barcoding regions supported the morphological identification. The barcoding sequences of the strains showed a high percentage of identity with the sequences reported in INSDC databases for the same species. The topology of the phylogenetic trees demonstrates that epilithic diatoms from Ecuador are closely related to those of same species isolated from other geographical regions. This study is a first attempt to establish a morphological and molecular taxonomic reference library for neotropical diatoms. This study demonstrates that it would be feasible to use the existing barcoding data for diatoms to develop molecular tools for the bioassessment of aquatic ecosystems in the Ecuadorian Andean region.