Structural insights into the targeting of mRNA GU-rich elements by the three RRMs of CELF1

The CUG-BP, Elav-like family (CELF) of RNA-binding proteins control gene expression at a number of different levels by regulating pre-mRNA splicing, deadenylation and mRNA stability. We present structural insights into the binding selectivity of CELF member 1 (CELF1) for GU-rich mRNA target sequences of the general form 5′-UGUN_xUGUN_yUGU and identify a high affinity interaction (K_d ∼ 100 nM for x = 2 and y = 4) with simultaneous binding of all three RNA recognition motifs within a single 15-nt binding element. RNA substrates spin-labelled at either the 3′ or 5′ terminus result in differential nuclear magnetic resonance paramagnetic relaxation enhancement effects, which are consistent with a non-sequential 2-1-3 arrangement of the three RNA recognition motifs on UGU sites in a 5′ to 3′ orientation along the RNA target. We further demonstrate that CELF1 binds to dispersed single-stranded UGU sites at the base of an RNA hairpin providing a structural rationale for recognition of CUG expansion repeats and splice site junctions in the regulation of alternative splicing.     

Contrasting patterns of genetic differentiation in Macaronesian lineages of Ilex (Aquifoliaceae)

Islands offer an interesting framework in which to study the effect of geographical isolation on population genetic differentiation. For plant species with high dispersal abilities, however, oceanic barriers may not represent a factor promoting strong population structure. In this work, we analysed seven nuclear microsatellite loci in Ilex (Aquifoliaceae), a bird‐dispersed plant group, to infer patterns of genetic differentiation among Macaronesian taxa: I. canariensis, I. perado ssp. lopezlilloi, I. perado ssp. platyphylla (Canary Islands) and I. perado ssp. azorica (Azores). In agreement with current taxonomic classification, our results revealed a high genetic differentiation between Ilex lineages (I. canariensis and the I. perado complex), and also supported previous hypotheses that these are the result of independent dispersal events to the islands. In contrast, genetic differentiation between I. perado ssp. azorica and the two subspecies from the Canaries was high, suggesting that taxonomic revision may be necessary. Levels of genetic variation at microsatellite loci in ssp. azorica were, in addition, the lowest reported among Macaronesian bird‐dispersed taxa. Lastly, low genetic differentiation was observed between subspecies occurring on the same island (sspp. platyphylla and lopezlilloi). In summary, our results revealed contrasting patterns between Macaronesian Ilex lineages: I. canariensis displayed moderate population structure across islands, whereas the I. perado complex showed strong differentiation among populations sampled on different islands. Thus, the Macaronesian Ilex taxa show that long‐distance dispersal syndromes (ornithochory) do not always ensure genetic connectivity across large areas in island systems. Plant groups that successfully colonized the islands on multiple occasions may have found barriers to gene flow within certain lineages. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 258–268.     

The impact of nandrolone decanoate and growth hormone on biosynthesis of steroids in rats

Growth hormone (GH) and anabolic androgenic steroids (AAS) are commonly used in sports communities. Several studies have suggested an association between GH and AAS. We have investigated the impact of GH in rats treated with nandrolone decanoate (ND). Male Wistar rats received ND (15 mg/kg) every third day during three weeks and were subsequently treated with recombinant human GH (1.0 IU/kg) for ten consecutive days. Plasma samples were collected and peripheral organs (i.e. heart, liver, testis and thymus) were dissected and weighed. Concentration of thirteen endogenous steroids was measured in the rat plasma samples using high specificity LC–MS/MS methods. Seven steroids were detected and quantified, and concentrations of estrone, testosterone, and androstenedione were significantly different among the groups, while concentrations of pregnenolone, DHEA, 17-hydroxyprogesterone and corticosterone were not altered. Administration of rhGH alone altered the plasma steroid distribution, and the results demonstrated significantly increased concentrations of plasma estrone as well as decreased concentrations of testosterone and androstenedione in the ND-treated rats. Administration of rhGH to ND-pretreated rats did not reverse the alteration of the steroid distribution induced by ND. Administration of ND decreased the weight of the thymus, and addition of rhGH did not reverse this reduction. However, rhGH administration induced an enlargement of thymus. Taken together, the plasma steroid profile differed in the four groups, i.e. control, AAS, rhGH and the combination of AAS and rhGH treatment.     

Programmable mechanical stimulation influences tendon homeostasis in a bioreactor system

Identification of functional programmable mechanical stimulation (PMS) on tendon not only provides the insight of the tendon homeostasis under physical/pathological condition, but also guides a better engineering strategy for tendon regeneration. The aims of the study are to design a bioreactor system with PMS to mimic the in vivo loading conditions, and to define the impact of different cyclic tensile strain on tendon. Rabbit Achilles tendons were loaded in the bioreactor with/without cyclic tensile loading (0.25 Hz for 8 h/day, 0–9% for 6 days). Tendons without loading lost its structure integrity as evidenced by disorientated collagen fiber, increased type III collagen expression, and increased cell apoptosis. Tendons with 3% of cyclic tensile loading had moderate matrix deterioration and elevated expression levels of MMP‐1, 3, and 12, whilst exceeded loading regime of 9% caused massive rupture of collagen bundle. However, 6% of cyclic tensile strain was able to maintain the structural integrity and cellular function. Our data indicated that an optimal PMS is required to maintain the tendon homeostasis and there is only a narrow range of tensile strain that can induce the anabolic action. The clinical impact of this study is that optimized eccentric training program is needed to achieve maximum beneficial effects on chronic tendinopathy management. Biotechnol. Bioeng. 2013; 110: 1495–1507. © 2012 Wiley Periodicals, Inc.