A 69-kDa RNA-binding protein from Xenopus oocytes recognizes a common motif in two vegetally localized maternal mRNAs.

Vg1 mRNA, a maternal message encoding a member of the transforming growth factor beta superfamily, undergoes localization to the vegetal cortex of Xenopus laevis oocytes during a narrow period of oogenesis. A 340-nucleotide sequence has been identified in Vg1 RNA that directs its vegetal localization [Mowry, K. L. & Melton, D. A. (1992) Science 255, 991-994]. To understand how cis- and trans-acting factors are involved in Vg1 mRNA localization, we have looked for specific interactions in vitro between oocyte proteins and Vg1 mRNA. S100 extracts of late-stage oocytes contain a protein-binding activity that protects specific regions of labeled Vg1 mRNA from degradation by RNase T1. The use of different regions of Vg1 RNA in competition reactions reveals two binding sites, both in the first half of the 3' untranslated region of Vg1 message. UV crosslinking predominantly labels a 69-kDa protein; saturation analysis and competitor studies indicate that this protein binds with a high affinity to the down-stream site, which corresponds to the 340-nucleotide vegetal localization sequence. Binding to this region is inhibited by another vegetally localized message, transforming growth factor beta 5 but is not inhibited by an animally localized RNA, An2. These data indicate that vegetally localized mRNAs share a binding motif that helps them achieve their intracellular distribution through specific RNA-protein interactions.

Involvement of corticotrophin releasing factor (CRF) in the thermogenic and anorexic actions of serotonin (5-HT) and related compounds.

The present study investigated the involvement of corticotrophin-releasing factor (CRF) in the thermogenic and anorexic actions of serotonin (5-HT) in the rat. Serotonergic compounds and CRF antibody were injected directly into the third ventricle of conscious, male Sprague-Dawley rats. Thermogenesis was measured as changes in whole body oxygen consumption by indirect calorimetry. Central injections of 5-HT (0.5-50 micrograms, i.c.v.) significantly increased resting oxygen consumption (VO2; maximum 12.5% increase), without obvious effects on behaviour. Similar increases in VO2 (12-17%) were observed following central injections of the 5-HT precursors, tryptophan (14 micrograms, i.c.v.) or 5-hydroxytryptophan (5-HTP, 20 micrograms, i.c.v.), and peripheral (10 mg/kg, i.p.) or central (30 micrograms, i.c.v.) injections of the 5-HT reuptake inhibitor, DL-fenfluramine. Administration of a polyclonal CRF antibody (3 microliters, i.c.v.) 10 min prior to serotonergic compounds, significantly reduced (77-106%) the increases in VO2 observed in response to central injections of 5-HTP (20 micrograms), 5-HT (50 micrograms) or peripheral injections of fenfluramine, but not those observed in response to either 30 micrograms fenfluramine (i.c.v.) or 20 micrograms 5-HT. Voluntary food intake was measured for 6 h in rats following 16 h starvation. Six-hour food intake was significantly reduced (30-60%) in rats given central injections of 5-HT or 5-HTP, and central or peripheral injections of fenfluramine.(ABSTRACT TRUNCATED AT 250 WORDS)