Sexual mimicry in hyenas

Genital masculinization in female spotted hyenas has been widely explained as an incidental consequence of high androgen levels. High androgen levels, in turn, were supposed to be favored because they led to adaptive aggressive behavior. Incidental androgenization is no longer a tenable hypothesis, however, because genital masculinization has been shown to proceed in the absence of androgenic steroids. Thus, an alternative hypothesis is required. The genitals of spotted hyena females are not simply masculinized, but exhibit a detailed physical resemblance to the male genitalia. In the absence of satisfactory alternative explanations, we propose that selection may have favored sexual mimicry in females because they are more likely than males to be targets of aggression from other females. Male-like camouflage could theoretically be protective in three contexts: neonate sibling aggression, infanticide by conspecific females, and interclan territoriality. Current data suggest that if sexual mimicry is important, its effects are strongest among infants.     

Viral complement regulators: the expert mimicking swindlers

The complement system is a principal bastion of innate immunity designed to combat a myriad of existing as well as newly emerging pathogens. Since viruses are obligatory intracellular parasites, they are continuously exposed to host complement assault and, therefore, have imbibed various strategies to subvert it. One of them is molecular mimicry of the host complement regulators. Large DNA viruses such as pox and herpesviruses encode proteins that are structurally and functionally similar to human regulators of complement activation (RCA), a family of proteins that regulate complement. In this review, we have presented the structural and functional aspects of virally encoded RCA homologs (vRCA), in particular two highly studied vRCAs, vaccinia virus complement control protein (VCP) and Kaposi's sarcoma-associated herpesvirus complement regulator (kaposica). Importance of these evasion molecules in viral pathogenesis and their role beyond complement regulation are also discussed.     

Batesian mimicry promotes pre‐ and postmating isolation in a snake mimicry complex

We evaluated whether Batesian mimicry promotes early‐stage reproductive isolation. Many Batesian mimics occur not only in sympatry with their model (as expected), but also in allopatry. As a consequence of local adaptation within both sympatry (where mimetic traits are favored) and allopatry (where nonmimetic traits are favored), divergent, predator‐mediated natural selection should disfavor immigrants between these selective environments as well as any between‐environment hybrids. This selection might form the basis for both pre‐ and postmating isolation, respectively. We tested for such selection in a snake mimicry complex by placing clay replicas of sympatric, allopatric, or hybrid phenotypes in both sympatry and allopatry and measuring predation attempts. As predicted, replicas with immigrant phenotypes were disfavored in both selective environments. Replicas with hybrid phenotypes were also disfavored, but only in a region of sympatry where previous studies have detected strong selection favoring precise mimicry. By fostering immigrant inviability and ecologically dependent selection against hybrids (at least in some habitats), Batesian mimicry might therefore promote reproductive isolation. Thus, although Batesian mimicry has long been viewed as a mechanism for convergent evolution, it might play an underappreciated role in fueling divergent evolution and possibly even the evolution of reproductive isolation and speciation.     

Formation of noncanonical DNA structures mediated by human ORC4, a protein component of the origin recognition complex

Many genomic sequences, DNA replication origins included, contain specific structural motifs prone to alternative base pairing. Structural rearrangements of DNA require specific environmental conditions and could be favored by chemical agents or proteins. To improve our understanding of alternative conformations of origins and the manner in which they form, we have investigated the effect of DNA-binding, AAA+ protein human ORC4 on single-stranded origin DNA or various oligonucleotides. Here we demonstrate that human ORC4 stimulated formation of inter- and intramolecular T.A.T triplexes and created novel structures, such as homoadenine duplexes. Adenine-based structures were held together by Hoogsteen hydrogen bonds, as demonstrated on 7-deaza-dAMP- or dAMP-containing substrates, and characterized by increased thermal stability. Adenine pairing occurred only in the presence of human ORC4, in a neutral buffer supplemented with ATP and Mg (2+) ions. The protein mutant that could not bind ATP was inactive in this reaction. Since the action of human ORC4 could be biologically important, its potential impact on DNA replication is discussed.     

Herpes simplex virus-induced keratitis: evaluation of the role of molecular mimicry in lesion pathogenesis

Viruses are suspected but usually unproven triggering factors in autoimmunity. One favored mechanism to explain the role of viruses in the genesis of autoimmunity is molecular mimicry. An immunoinflammatory blinding lesion called herpetic stromal keratitis (HSK) that follows ocular infection with herpes simplex virus (HSV) is suggested to result from a CD4(+) T-cell response to a UL6 peptide of HSV that cross-reacts with a corneal autopeptide shared with the immunoglobulin G2a(b) (IgG2a(b)) isotype. The present report reevaluates the molecular mimicry hypothesis to explain HSK pathogenesis. Our results failed to reveal cross-reactivity between the UL6 and IgG2a(b) peptides or between peptide reactive T cells and HSV antigens. More importantly, animals infected with HSV failed to develop responses that reacted with either peptide, and infection with a recombinant vaccinia UL6 vector failed to cause HSK, in spite of generating UL6 reactivity. Other lines of evidence also failed to support the molecular mimicry hypothesis, such as the failure to affect HSK severity upon tolerization of susceptible BALB/c and B-cell-deficient mice with IgG2a(b) or UL6 peptides. An additional study system revealed that HSK could be induced in mouse strains, such as the OT2 x RAG1(-/-) mice (T cell receptor transgenic recognizing OVA(323-339)) that were unable to produce CD4(+) T-cell responses to any detectable HSV antigens. Our results cast doubt on the molecular mimicry hypothesis as an explanation for the pathogenesis of HSK and indicate that if autoimmunity is involved its likely proceeds via a bystander activation mechanism.     

Diversity of warning signal and social interaction influences the evolution of imperfect mimicry

Mimicry, the resemblance of one species by another, is a complex phenomenon where the mimic (Batesian mimicry) or the model and the mimic (Mullerian mimicry) gain an advantage from this phenotypic convergence. Despite the expectation that mimics should closely resemble their models, many mimetic species appear to be poor mimics. This is particularly apparent in some systems in which there are multiple available models. However, the influence of model pattern diversity on the evolution of mimetic systems remains poorly understood. We tested whether the number of model patterns a predator learns to associate with a negative consequence affects their willingness to try imperfect, novel patterns. We exposed week‐old chickens to coral snake (Micrurus) color patterns representative of three South American areas that differ in model pattern richness, and then tested their response to the putative imperfect mimetic pattern of a widespread species of harmless colubrid snake (Oxyrhopus rhombifer) in different social contexts. Our results indicate that chicks have a great hesitation to attack when individually exposed to high model pattern diversity and a greater hesitation to attack when exposed as a group to low model pattern diversity. Individuals with a fast growth trajectory (measured by morphological traits) were also less reluctant to attack. We suggest that the evolution of new patterns could be favored by social learning in areas of low pattern diversity, while individual learning can reduce predation pressure on recently evolved mimics in areas of high model diversity. Our results could aid the development of ecological predictions about the evolution of imperfect mimicry and mimicry in general.     

DNA bending creates favored sites for retroviral integration: an explanation for preferred insertion sites in nucleosomes.

The choice of retroviral integration sites is strongly influenced by chromatin: integration in vitro occurs more efficiently into nucleosomal DNA than into naked DNA, and a characteristic pattern of preferred insertion sites with a 10 bp periodicity is observed at the outer face of the nucleosomal DNA. At least three features of nucleosomal DNA could be responsible for the creation of these favored sites: the presence of histones, attachment of the DNA to a protein surface, and DNA bending. To test each of these possibilities, we studied integration in vitro with human immunodeficiency virus and murine leukemia virus integrases into four model targets that mimic features of nucleosomal DNA: (i) catabolite activator protein-DNA complexes; (ii) lac repressor-operator complexes; (iii) lac repressor-induced loops; and (iv) intrinsically bent A-tract DNA. We found that bending of the target DNA can create favored integration sites at the outer face of the helix, irrespective of whether the bent DNA is attached to a protein surface. Our findings offer an explanation for the preferred usage of nucleosomes as integration targets. In addition, they suggest that bending of the target DNA might be an intrinsic feature of the integration reaction.     

DNA mimicry by proteins and the control of enzymatic activity on DNA

Cells are unable to perform any function on their DNA in the absence of proteins, and it is of vital importance that these proteins only perform their function at appropriate times during the cell cycle. Thus, DNA-binding proteins are always controlled by a wide range of other factors, primarily other proteins. These controlling factors usually block access of the protein to the DNA, often operating by simple competitive inhibition. However, it has recently been demonstrated that DNA-binding proteins can be controlled by the direct binding of the control protein to the DNA-binding site on the first protein. The structures of these control proteins have revealed that they mimic the structure and electrostatics of DNA. This review highlights the roles of DNA mimics in the control of DNA-binding proteins, suggests other possible candidate proteins using DNA mimicry, and puts forward a range of potential uses of DNA mimics.     

Trinucleotide repeats are clustered in regulatory genes in Saccharomyces cerevisiae

The genome of Saccharomyces cerevisiae contains numerous unstable microsatellite sequences. Mononucleotide and dinucleotide repeats are rarely found in ORFs, and when present in an ORF are frequently located in an intron or at the C terminus of the protein, suggesting that their instability is deleterious to gene function. DNA trinucleotide repeats (TNRs) are found at a higher-than-expected frequency within ORFs, and the amino acids encoded by the TNRs represent a biased set. TNRs are rarely conserved between genes with related sequences, suggesting high instability or a recent origin. The genes in which TNRs are most frequently found are related to cellular regulation. The protein structural database is notably lacking in proteins containing amino acid tracts, suggesting that they are not located in structured regions of a protein but are rather located between domains. This conclusion is consistent with the location of amino acid tracts in two protein families. The preferred location of TNRs within the ORFs of genes related to cellular regulation together with their instability suggest that TNRs could have an important role in speciation. Specifically, TNRs could serve as hot spots for recombination leading to domain swapping, or mutation of TNRs could allow rapid evolution of new domains of protein structure.     

Macromolecular mimicry

Some proteins have been shown to mimic the overall shape and structure of nucleic acids. For some of the proteins involved in translating the genetic information into proteins on the ribosome particle, there are indications that such observations of macromolecular mimicry even extend to similarity in interaction with and function on the ribosome. A small number of structural results obtained outside the protein biosynthesis machinery could indicate that the concept of macromolecular mimicry between proteins and nucleic acids is more general. The implications for the function and evolution of protein biosynthesis are discussed.     

黄鳝性腺高表达的核糖体蛋白基因

采用高密点阵技术从黄鳝雄性性腺cDNA文库中获得8个克隆,序列分析和BLAST结果显示它们编码的蛋白质分别与40S核糖体蛋白S4,S9,S16,S17,S20和60S核糖体蛋白L7, L18a,L29高度同源。 根据黄鳝RP蛋白序列和其他物种的相应同源序列构建ML系统发生树,显示核糖体蛋白基因在进化中高度保守。核糖体蛋白基因不仅可作为分子进化分析的有利工具,而且从它们的表达模式显示RP基因除具有看家基因的功能外,很有可能参与包括性腺分化等过程的发育调控。Abstract: 8 cDNA clones have been isolated from a cDNA library prepared from swamp eel testies by macroarray. DNA sequence analysis and database search showed that they encode 8 proteins which are highly homologous to 40S ribosomal proteins S4,S9,S16,S17,S20 and 60S riobosomal proteins L7, L18a,L29. Phylogenetic trees (ML) based on ribosomal protein genes from swamp eel and other organisms has been reconstructed, which showed that ribosomal protein genes were highly conserved during evolution. These results suggested that ribosomal protein genes as house keeping genes may play roles in developmental regulation such as sexual differentiation and can also be used as markers for the study of molecular evolution.     

Why are there so many mimicry rings? Correlations between habitat,behaviour and mimicry in Heliconius butterflies

In the new world tropics there is an extravagant array of sympatric butterfly mimicry rings. This is puzzling under strictly coevolutionary (Müllerian) mimicry: all unpalatable species should converge as ‘co-mimics' to the same pattern. If mimicry has usually evolved in unpalatable species by one-sided (Batesian) evolution, however, it is easy to see that mimicry rings centred on different models could remain distinct. If mimicry rings were also segregated by habitat, a diversity of mimicry rings could be stabilized. In this paper we report correlations between behaviour and mimicry of nine unpalatable Heliconius species. It is already known that co-mimics fly in similar habitats, and non-mimics fly in different habitats, although there is much overlap. Contrary to a previous report, we find little difference in flight heights of heliconiine mimicry rings; all species fly from ground level to the canopy. However, co-mimics roost at night in similar habitats and at similar heights above the ground, but in different habitats and at different heights from species in other mimicry rings. Heliconius (especially the erato taxonomic group) are renowned for roosting gregariously; and co-mimics roost gregariously with each other more often than with non-mimics. Gregarious roosting is therefore common between species, as well as within species. There are thus strong links between mimicry and behavioural ecology in Heliconius. The paradoxical correlation between nocturnal roosting and visual mimicry is presumably explained by bird predation at dusk when roosts are forming, or at dawn before they have disbanded. Direct evidence of predation is lacking, but there are high rates of disturbance by birds at these times. These results, together with knowledge of the phylogeny of Heliconius, suggest that species from the melpomene-group of Heliconius have radiated to occupy mimetic niches protected by model species in the Ithomiinae and the erato-group of Heliconius. A variety of sympatric mimicry rings is apparently maintained because key models fail to converge, while more rapidly-evolving unpalatable mimics evolve towards the colour patterns of the models. The maintenance of mimetic diversity would be aided by the habitat and behavioural differences between mimicry rings revealed here, provided that different predators are found in different habitats. This explanation for the maintenance of multiple mimicry rings is more plausible for Heliconius mimicry than alternatives based on visual mating constraints, thermal ecology, or camouflage.