This Week in PNAS
Ecology
Frogs integrate temporospatial cues in aggressive behavior
Research by Peter Narins et al. suggests that the neural processes that come into play when humans are “tricked” by ventriloquists may also elucidate the neural processes of aggressive behavior in amphibians. Cross-modal spatial integration in the brain “binds” separate auditory and visual cues over a limited temporospatial range, and such integration is involved in the processing of sound from one source that seems to emanate from another. Narins et al. explored these mechanisms in males of the dart-poison frog, Epipedobates femoralis, which defend their territory in response to visual and auditory cues of intruders. The researchers used an electromechanical frog emanating an auditory cue (natural call from a loudspeaker) and a visual cue (vocal-sac inflations and deflations) to trigger aggressive territory-defending behavior in the frogs. In one set of experiments, a time delay of up to 8.7 s was used between the visual and auditory cues, and in a second set, the visual and auditory cues were put out at the same time but at different locations between 12 and 50 cm. Despite the temporal and spatial disparities, in both instances aggressive behavior was observed when there was at least some temporal overlap of the stimuli. The authors also found that a range of temporal and spatial disparities exists for which aggressive behavior persists. According to the researchers, these results demonstrate that temporal and spatial integration may be reliably estimated in a freely behaving animal in its natural habitat, and aggressive behavior in this species may be used as an index of cross-modal integration.
“Cross-modal integration in a dart-poison frog” by Peter M. Narins, Daniela S. Grabul, Kiran K. Soma, Philippe Gaucher, and Walter Hödl (see pages 2425–2429)
Evolution
MADS-box evolution in green algae
Yoichi Tanabe et al. characterize the MADS-box transcription factor genes in charophycean green algae, the closest living relatives of land plants. Previous research has shown that the MADS-box gene family regulates development in flowering plants and may be involved in morphological plant evolution. Tanabe et al. extracted total RNA from three charophycean species: the stonewort Chara globularis, the coleochaete Coleochaete scutata, and the desmid Closterium peracerosum–strigosum–littorale complex. The researchers cloned one MADS-box cDNA from each species and found homology of the charophyceans' genes to other MIKCc- and MIKC*-type MADS-boxes. The exon–intron structures of the coleochaete gene were mostly identical to those of land plant MIKCc-type genes, whereas the stonewort and desmid genes contained additional introns. The authors determined that the stonewort MADS-box gene is expressed exclusively in tissues containing the reproductive organs, quantified the temporal expression of the desmid complex MADS-box gene, and observed a gradual increase in transcript expression that peaked 4 h after vegetative cells of two different mating types were cultivated together.
“Characterization of MADS-box genes in charophycean green algae and its implication for the evolution of MADS-box genes” by Yoichi Tanabe, Mitsuyasu Hasebe, Hiroyuki Sekimoto, Tomoaki Nishiyama, Masakazu Kitani, Katrin Henschel, Thomas Münster, Günter Theissen, Hisayoshi Nozaki, and Motomi Ito (see pages 2436–2441)
Genetics, Computer Sciences
Expanding computational RNomics
In the burgeoning field of computational RNomics, noncoding RNAs (ncRNAs) are involved in gene regulation and include cis-acting elements of mRNAs and maturation of other RNA molecules. Stefan Washietl et al. describe an efficient method to detect functional RNAs. The method combines two approaches: (i) assessing the evolutionary conservation of RNA secondary structure and (ii) efficient measurement of thermodynamic stability. To evaluate the technique, the researchers screened sequence alignments from the Comparative Regulatory Genomics (CORG) database, which compiles conserved noncoding elements in upstream regions of orthologous genes from humans, mice, rats, Fugu, and zebrafish. All of the known ncRNAs and structured cis-acting elements were identified with high significance. The authors also found evidence for other conserved RNA secondary structures not previously described. According to the authors, the method has yielded favorable results for a small number of aligned sequences, is suitable for genomic screening on a larger scale, and may be more rapid than approaches currently used to detect functional RNAs.
“Fast and reliable prediction of noncoding RNAs” by Stefan Washietl, Ivo L. Hofacker, and Peter F. Stadler (see pages 2454–2459)
Immunology
Resistance to Legionnaires' disease
Thomas Hawn et al. report that single-nucleotide polymorphisms in Toll-like receptor 4 (TLR4) are associated with a resistance to Legionnaires' disease. Toll-like receptors recognize a wide variety of pathogens and play a central role in the regulation of innate immune responses. Legionella bacteria, which causes community-acquired pneumonia, are recognized by several Toll-like receptors; however, the influence of host immunogenetic factors on susceptibility is poorly understood. The authors used a case-control study to compare the allele frequencies of two polymorphisms, A896G and C1196T, of a Legionnaires' disease outbreak in The Netherlands in 1999. A control group of individuals, who were exposed at the same outbreak but did not develop pneumonia, were used for matched and unmatched comparisons. The authors purified genomic DNA from the infected and uninfected individuals and sequenced their TLR4 genes. Previous studies had suggested that these TLR4 polymorphisms are associated with an increased risk of infection. However, the researchers found that, in a matched group comparison, the A896G allele showed a protective association with an odds ratio of 0.27. Allele C1196T, which cosegregated with allele 896G, had identical associations. The authors report that this protective association of TLR4 with Legionella suggests that the same innate immune receptor mediates inflammatory responses with clinical consequences that vary for different pathogens.
“Toll-like receptor 4 polymorphisms are associated with resistance to Legionnaires' disease” by Thomas R. Hawn, Annelies Verbon, Marta Janer, Lue Ping Zhao, Bruce Beutler, and Alan Aderem (see pages 2487–2489)
Antrhopology
Grammar emerges early in new language
Al-Sayyid Bedouin Sign Language (ABSL) serves as an alternative language in an isolated village of ≈3,500 deaf and hearing people in Israel. This young language arose spontaneously and independently and developed a distinct grammatical structure early in its evolution, researchers report. Through translated video clips of native second-generation signers, Wendy Sandler et al. found the accepted word order of ABSL within sentences to be subject–object–verb and within phrases to be head–modifier. Because word order is one of the most important organizing principles in any language, its appearance in this young language is remarkable. Unlike other new languages, such as creoles and Nicaraguan sign language, ABSL is reported to have grown within a socially stable, existing community. A pattern of consanguineous marriage and recessive deafness has ensured that deaf persons are well distributed throughout the group's population, and ABSL is shown to be transmitted within families across generations. Also, the grammatical structure identified in ABSL showed no influence from either ambient spoken languages in the community or the sign language in the surrounding area. Now in its third generation of use, ABSL may help highlight the fundamental nature of all human languages.
“The emergence of grammar: Systematic structure in a new language” by Wendy Sandler, Irit Meir, Carol Padden, and Mark Aronoff (see pages 2661–2665)
Figures and Tables
Amphibian aggressive behavior stimuli.
Charophycean green algae have floral homeotic gene homologs.
Graphing RNA class probability.
