The mitochondrial uncoupling protein (UCP) is responsible for the thermogenic function of brown fat, and it is a molecular marker of the brown adipocyte cell type. Retinoic acid (RA) increased UCP mRNA levels severalfold in brown adipocytes differentiated in culture. This induction was independent of adrenergic pathways or protein synthesis. RA stimulated ucp gene expression regardless of the stage of brown adipocyte differentiation. In transient transfection experiments RA induced the expression of chloramphenicol acetyltransferase vectors driven by 4.5 kilobases of the 5'-noncoding region of the rat ucp gene, and co-transfection of expression vectors for RA receptors enhanced the action of RA. Retinoic acid receptor alpha was more effective than retinoid X receptor in promoting RA action, whereas a mixture of the two was the most effective. The RA-responsive region in the ucp gene was located at -2469/-2318 and contains three motifs (between -2357 and -2330) of the consensus half-sites characteristic of retinoic acid response elements. This 27-base pair sequence specifically binds purified retinoic acid receptor alpha as well as related proteins from brown fat nuclei. In conclusion, a novel potential regulatory pathway of brown fat development and thermogenic function has been recognized by identifying RA as a transcriptional activator of the ucp gene.

El artículo presenta las principales opciones teóricas y metodológicas de un proyecto de investigación cuyo objetivo principal es el estudio de algunos mecanismos de influencia educativa que se manifiestan en, o actúan a través de, la interacción profesor/grupo de alumnos y adulto/niño. Utilizando como punto de partida el concepto de interactividad, término acuñado para designar las formas de organización de la actividad conjunta en torno al contenido o tarea que están llevando a cabo los participantes, se analizan dos mecanismos de influencia educativa: la cesión y el traspaso progresivos del control y la responsabilidad y la construcción progresiva de sistemas de significados compartidos.

The aim of this paper is to understand how certain educational supports promote preservice teachers' learning to reflect in collaborative settings. To address this issue, we present a case study on collaborative reflection among 14 preservice teachers and one teacher educator over the course of five weekly consecutive sessions. The results suggest that collaborative reflection can be supported by organizing the process according to a twofold dynamic: from analysis to synthesis, and from open facilitation to directive facilitation. Six different types of assistance related to this dynamic, and provided by the teacher educator, are identified and qualitatively described: framing, oppositional voice, counterpoising alternatives, asking for the dilemma, problematizing, and modelling.

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The intracellular pathways and receptors mediating the effects of retinoic acid (RA) on the brown-fat-uncoupling-protein-1 gene (ucp-1) have been analysed. RA activates transcription of ucp-1 and the RA receptor (RAR) is known to be involved in this effect. However, co-transfection of an expression vector for retinoid-X receptor (RXR) increases the action of 9-cis RA but not the effects of all-trans RA on the ucp-1 promoter in brown adipocytes. Either RAR-specific ¿p-[(E)-2-(5,6,7,8,-tetrahydro-5,5,8, 8-tetramethyl-2-naphthalenyl)-1-propenyl]benzoic acid¿ or RXR-specific [isopropyl-(E,E)-(R,S)-11-methoxy-3,7, 11-trimethyldodeca-2,4-dienoate, or methoprene] synthetic compounds increase the expression of UCP-1 mRNA and the activity of chloramphenicol acetyltransferase expression vectors driven by the ucp-1 promoter. The RXR-mediated action of 9-cis RA requires the upstream enhancer region at -2469/-2318 in ucp-1. During brown-adipocyte differentiation RXRalpha and RXRgamma mRNA expression is induced in parallel with UCP-1 mRNA, whereas the mRNA for the three RAR subtypes, alpha, beta and gamma, decreases. Co-transfection of murine expression vectors for the different RAR and RXR subtypes indicates that RARalpha and RARbeta as well as RXRalpha are the major retinoid-receptor subtypes capable of mediating the responsiveness of ucp-1 to retinoids. It is concluded that the effects of retinoids on ucp-1 transcription involve both RAR- and RXR-dependent signalling pathways. The responsiveness of brown adipose tissue to retinoids in vivo relies on a complex combination of the capacity of RAR and RXR subtypes to mediate ucp-1 induction and their distinct expression in the differentiated brown adipocyte.