Sperm number trumps sperm size in mammalian ejaculate evolution

Postcopulatory sexual selection is widely accepted to underlie the extraordinary diversification of sperm morphology. However, why does it favour longer sperm in some taxa but shorter in others? Two recent hypotheses addressing this discrepancy offered contradictory explanations. Under the sperm dilution hypothesis, selection via sperm density in the female reproductive tract favours more but smaller sperm in large, but the reverse in small, species. Conversely, the metabolic constraint hypothesis maintains that ejaculates respond positively to selection in small endothermic animals with high metabolic rates, whereas low metabolic rates constrain their evolution in large species. Here, we resolve this debate by capitalizing on the substantial variation in mammalian body size and reproductive physiology. Evolutionary responses shifted from sperm length to number with increasing mammalian body size, thus supporting the sperm dilution hypothesis. Our findings demonstrate that body-size-mediated trade-offs between sperm size and number can explain the extreme diversification in sperm phenotypes.     

Drosophila p24 homologues eclair and baiser are necessary for the activity of the maternally expressed Tkv receptor during early embryogenesis

p24 proteins are assumed to play an important role in the transport of secreted and transmembrane proteins into membranes. However, only few cargo proteins are known that partially, but in no case completely require p24 proteins for membrane transport. Here, we show that two p24 proteins are essential for dorsoventral patterning of Drosophila melanogaster embryo. Mutations in the genes, eclair (eca) and baiser (bai), encoding two p24 proteins reduce signalling by the TGF-beta homologue, Dpp, in early embryos. This effect is strictly maternal and specific to early embryogenesis, as Dpp signalling in other contexts is not notably affected. We provide genetic evidence that in the absence of eca or bai function in the oocyte, the maternally expressed type I TGF-beta receptor Tkv is not active. We propose that during early embryogenesis eca and bai are specifically required for the activity of the maternal Tkv, while the zygotic Tkv is not affected in the mutant embryos. Mutations in either eca or bai are sufficient for the depletion of Tkv activity and no enhancement of the phenotypes was observed in embryos derived from oocytes mutant for both genes. The dependence of maternal Tkv protein on the products of p24 genes may serve as an in vivo model for studying p24 proteins.     

The upper cytokine-binding module and the Ig-like domain of the leukaemia inhibitory factor (LIF) receptor are sufficient for a functional LIF receptor complex.

To elucidate the function of the two cytokine-binding modules (CBM) of the leukemia inhibitory factor receptor (LIFR), receptor chimeras of LIFR and the interleukin-6 receptor (IL-6R) were constructed. Either the NH(2)-terminal (chimera RILLIFdeltaI) or the COOH-terminal LIFR CBM (chimera RILLIFdeltaII) were replaced by the structurally related CBM of the IL-6R which does not bind LIF. Chimera RILLIFdeltaI is functionally inactive, whereas RILLIFdeltaII binds LIF and mediates signalling as efficiently as the wild-type LIFR. Deletion mutants of the LIFR revealed that both the NH(2)-terminal CBM and the Ig-like domain of the LIFR are involved in LIF binding, presumably via the LIF site III epitope. The main function of the COOH-terminal CBM of the LIFR is to position the NH(2)-terminal CBM and the Ig-like domain, so that these can bind to LIF. In analogy to a recently published model of the IL-6R complex, a model of the active LIFR complex is suggested which positions the COOH-terminal CBM at LIF site I and the NH(2)-terminal CBM and the Ig-like domain at site III. An additional contact is postulated between the Ig-like domain of gp130 and the NH(2)-terminal CBM of the LIFR.     

Recent advances in chlorophyll biosynthesis and breakdown in higher plants

Chlorophyll (Chl) has unique and essential roles in photosynthetic light-harvesting and energy transduction, but its biosynthesis, accumulation and degradation is also associated with chloroplast development, photomorphogenesis and chloroplast-nuclear signaling. Biochemical analyses of the enzymatic steps paved the way to the identification of their encoding genes. Thus, important progress has been made in the recent elucidation of almost all genes involved in Chl biosynthesis and breakdown. In addition, analysis of mutants mainly in Arabidopsis, genetically engineered plants and the application of photo-reactive herbicides contributed to the genetic and regulatory characterization of the formation and breakdown of Chl. This review highlights recent progress in Chl metabolism indicating highly regulated pathways from the synthesis of precursors to Chl and its degradation to intermediates, which are not longer photochemically active.     

Cellular recognition of trimyristoylated peptide or enterobacterial lipopolysaccharide via both TLR2 and TLR4

Evidence for specific and direct bacterial product recognition through toll-like receptors (TLRs) has been emphasized recently. We analyzed lipopeptide analogues and enterobacterial lipopolysaccharide (eLPS) for their potential to activate cells through TLR2 and TLR4. Whereas bacterial protein palmitoylated at its N-terminal cysteine and N-terminal peptides derived thereof are known to induce TLR2-mediated cell activation, a synthetic acylhexapeptide mimicking a bacterial lipoprotein subpopulation for which N-terminal trimyristoylation is characteristic (Myr(3)CSK(4)) activated cells not only through TLR2 but also through TLR4. Conversely, highly purified eLPS triggered cell activation through overexpressed TLR2 in the absence of TLR4 expression if CD14 was coexpressed. Accordingly, TLR2(-/-) macrophages prepared upon gene targeting responded to Myr(3)CSK(4) challenge, whereas TLR2(-/-)/TLR4(d/d) cells were unresponsive. Through interferon-gamma (IFNgamma) priming, macrophages lacking expression of functional TLR4 and/or MD-2 acquired sensitivity to eLPS, whereas TLR2/TLR4 double deficient cells did not. Not only TLR2(-/-) mice but also TLR4(-/-) mice were resistant to Myr(3)CSK(4) challenge-induced fatal shock. d-Galactosamine-sensitized mice expressing defective TLR4 or lacking TLR4 expression acquired susceptibility to eLPS-driven toxemia upon IFNgamma priming, whereas double deficient mice did not. Immunization toward ovalbumin using Myr(3)CSK(4) as adjuvant was ineffective in TLR2(-/-)/TLR4(-/-) mice yet effective in wild-type, TLR2(-/-), or TLR4(-/-) mice as shown by analysis of ovalbumin-specific serum Ig concentration. A compound such as Myr(3)CSK(4) whose stimulatory activity is mediated by both TLR2 and TLR4 might constitute a preferable adjuvant. On the other hand, simultaneous blockage of both of the two TLRs might effectively inhibit infection-induced pathology.     

ErbB-2 and met reciprocally regulate cellular signaling via plexin-B1

Sema4D-induced activation of plexin-B1 has been reported to evoke different and sometimes opposing cellular responses. The mechanisms underlying the versatility of plexin-B1-mediated effects are not clear. Plexin-B1 can associate with the receptor tyrosine kinases ErbB-2 and Met. Here we show that Sema4D-induced activation and inactivation of RhoA require ErbB-2 and Met, respectively. In breast carcinoma cells, Sema4D can have pro- and anti-migratory effects depending on the presence of ErbB-2 and Met, and the exchange of the two receptor tyrosine kinases is sufficient to convert the cellular response to Sema4D from pro- to anti-migratory and vice versa. This work identifies a novel mechanism by which plexin-mediated signaling can be regulated and explains how Sema4D can exert different biological activities through the differential association of its receptor with ErbB-2 and Met.     

Insights into Mechanisms and Proteomic Characterisation of Pseudomonas aeruginosa Adaptation to a Novel Antimicrobial Substance

Antibiotic resistance has been reported since the introduction of synthetic antibiotics. Bacteria, such as one of the most common nosocomial pathogens P. aeruginosa, adapt quickly to changing environmental conditions, due to their short generation time. Thus microevolutional changes can be monitored in situ. In this study, the microevolutional process of Pseudomonas aeruginosa PAO1 resistance against a recently developed novel antibacterial zinc Schiff-base (ZSB) was investigated at the proteome level. After extended exposure to ZSB the passaged strain differed in tolerance against ZSB, with the adapted P. aeruginosa PAO1 exhibiting 1.6 times higher minimal inhibitory concentration. Using Two-dimensional Difference Gel Electrophoresis, the changes in the proteome of ZSB adapted P. aeruginosa PAO1 were examined by comparison with the non-adapted P. aeruginosa PAO1. The proteome of the adapted P. aeruginosa PAO1 strain differed significantly from the non-adapted in the abundance of two proteins when both strains were grown under stressing conditions. One protein could be identified as the outer membrane protein D that plays a role in uptake of basic amino acids as well as in carbapeneme resistance. The second protein has been identified as alkyl peroxide reductase subunit F. Our data indicated a slight increase in abundance of alkyl peroxide reductase F (AhpF) in the case of ZSB passaged P. aeruginosa PAO1. Higher abundance of Ahp has been discussed in the literature as a promoter of accelerated detoxification of benzene derivatives. The observed up-regulated AhpF thus appears to be connected to an increased tolerance against ZSB. Changes in the abundance of proteins connected to oxidative stress were also found after short-time exposure of P. aeruginosa PAO1 to the ZSB. Furthermore, adapted P. aeruginosa PAO1 showed increased tolerance against hydrogen peroxide and, in addition, showed accelerated degradation of ZSB, as determined by HPLC measurements.     

Apoplastic and cytosolic expression of full‐size antibodies and antibody fragments in Nicotiana tabacum

We compared the expression of a functional recombinant TMVspecific fullsize antibody (rAb29) in both the apoplast and cytosol of tobacco plants and a single chain antibody fragment (scFv29), derived from rAb29, was expressed in the cytosol. Cloned heavy and light chain cDNAs of fullsize rAb29, which binds to TMV coat protein monomers, were integrated into the plant expression vector pSS. The fullsize rAb29 was expressed in the cytosol and targeted to the apoplast by including the original murine antibody leader sequences. Levels of functional fullsize rAb29 expression were high in the apoplast (up to 8.5g per gram leaf tissue), whereas cytosolic expression was low or at the ELISA detection limit. Sequences of the variable domains of rAb29 light and heavy chain were used to generate the single chain antibody scFv29, which was expressed in the periplasmic space of E.coli and showed the same binding specificity as fullsize rAb29. In addition, scFv29 was functionally expressed in the cytosol of tobacco plants and plant derived scFv29 maintained same binding specificity to TMVcoat protein monomers as rAb29.     

Expression of Eukaryotic Initiation Factor 5A and Hypusine Forming Enzymes in Glioblastoma Patient Samples: Implications for New Targeted Therapies

Glioblastomas are highly aggressive brain tumors of adults with poor clinical outcome. Despite a broad range of new and more specific treatment strategies, therapy of glioblastomas remains challenging and tumors relapse in all cases. Recent work demonstrated that the posttranslational hypusine modification of the eukaryotic initiation factor 5A (eIF-5A) is a crucial regulator of cell proliferation, differentiation and an important factor in tumor formation, progression and maintenance. Here we report that eIF-5A as well as the hypusine-forming enzymes deoxyhypusine synthase (DHS) and deoxyhypusine hydroxylase (DOHH) are highly overexpressed in glioblastoma patient samples. Importantly, targeting eIF-5A and its hypusine modification with GC7, a specific DHS-inhibitor, showed a strong antiproliferative effect in glioblastoma cell lines in vitro, while normal human astrocytes were not affected. Furthermore, we identified p53 dependent premature senescence, a permanent cell cycle arrest, as the primary outcome in U87-MG cells after treatment with GC7. Strikingly, combined treatment with clinically relevant alkylating agents and GC7 had an additive antiproliferative effect in glioblastoma cell lines. In addition, stable knockdown of eIF-5A and DHS by short hairpin RNA (shRNA) could mimic the antiproliferative effects of GC7. These findings suggest that pharmacological inhibition of eIF-5A may represent a novel concept to treat glioblastomas and may help to substantially improve the clinical course of this tumor entity.