The independence of myogenesis and chondrogenesis in micromass cultures of chick wing buds

Micromass cultures prepared from stage 23, 24, or 25 chick wing buds and cultured under identical conditions produce similar numbers of myoblasts. After treatment with the DNA synthesis inhibitor cytosine-1-beta-D-arabinofuranoside, [3H]thymidine labeling and autoradiography of the cultures show that the increase in myoblast number during the first 48 hr of culture is due primarily to cell division. Micromass cultures prepared from proximal and distal portions of stage 23 or 24 wing buds have very different chondrogenic potentials in vitro (B.J. Swalla, E.M. Owens, T.F. Linsenmayer, and M. Solursh (1983). Dev. Biol. 97, 59-69) but a similar myogenic potential under these culture conditions. Medium supplements that significantly enhance chondrogenesis by proximal cell cultures, such as low serum or 1 mM db cyclic AMP, do not affect the number of myoblasts per unit area of culture during the first 3 days. Muscle cells are eventually reduced in number in whole limb micromass cultures, yet persist as long as 6 days in proximal and distal cultures. These results suggest that myogenic cells are already committed in the early limbs but are inhibited from differentiation in situ until a later time. Myogenesis and chondrogenesis occur independently in culture, consistent with the idea that these two differentiated cells are derived from two separate cell populations. Furthermore, treatments which enhance chondrogenesis do not act indirectly by killing the myoblast population in these cultures.     

Effects of Hunting on Response Behaviors of Wild Reindeer

ABSTRACT Because wild reindeer (Rangifer tarandus) are hunted in southern Norway, reindeer may perceive all recreationists as threats. Potential adverse effects of hunting on reindeer behavior may be exacerbated by other forms of recreation because the number of skiers and hikers in areas inhabited by reindeer has also increased. The Norefjell-Reinsjøfjell wild reindeer area is used extensively for recreation and tourism. Reindeer hunting was introduced in the area in 1992, and harvest rate has been stable at about 38% of winter herd size. We recorded behavioral responses of reindeer to a person approaching directly on foot or skis during 1992 and again in 2002–2006. Compared to 1992, flight-initiation distance increased and fewer groups assessed the observer before taking flight during 2002–2006. In winter, when reindeer are usually comparably more vigilant than in other seasons, flight-initiation distance increased from only 60 m to 115 m and escape distance decreased from 400 m to 210 m. Neither alert distance, calf carcass weights (23.6 ± 0.7 [SE] kg to 22.4 ± 0.2 kg), nor reindeer herd size (661 ± 73 to 579 ± 15) changed during the 15 years of our study. Reindeer appeared to habituate to the observer because they initiated flight at shorter distances as the number of approaches on the same day increased. In Norefjell-Reinsjøfjell, encounters with a person on foot or skis did not result in behavioral responses likely to entail substantial energy costs for reindeer; therefore, hunting at current levels appears compatible with other recreational activities.     

A new metazoan from the Vendian of the White Sea,Russia, with possible affinities to the ascidians

Two specimens recovered from late Neoproterozoic shallow marine sediments of northern Russia may be the oldest known ascidians. Dated at around 555 Ma, these, together with the younger Ausia from the Nama Group in southwestern Africa, are probably relatives of these invertebrate chordates, which have a deep time origin predicted by molecular studies.     

Screening Global Positioning System Location Data for Errors Using Animal Movement Characteristics

Abstract: Animal locations estimated by Global Positioning System (GPS) inherently contain errors. Screening procedures used to remove large positional errors often trade data accuracy for data loss. We developed a simple screening method that identifies locations arising from unrealistic movement patterns. When applied to a large data set of moose (Alces alces) locations, our method identified virtually all known errors with minimal loss of data. Thus, our method for screening GPS data improves the quality of data sets and increases the value of such data for research and management.     

Vestigial Brain Melanocyte Development During Embryogenesis of an Anural Ascidian

Anural development was examined in the ascidian Bostrichobranchus digonas using specific markers for differentiated urodele ascidian larval cells and tissues. In this ovoviviparous anural ascidian, eggs, embryos and developing juveniles were present in the gonads, brood sacs, and atrial cavity, respectively. Morphological studies indicated that B. digonas embryos do not develop into tailed larvae with an extended notochord and differentiated muscle cells. In addition, these embryos lack detectable expression of the muscle-specific markers acetylcholinesterase, alpha actin, and myosin heavy chain. In striking contrast to other anural ascidian embryos, however, B. digonas embryos can develop tyrosinase in several melanocyte precursor cells and eventually form a brain pigment cell. The melanocyte does not become part of a definitive brain sensory organ (otolith) and subsequently disappears during metamorphosis. A period of tyrosinase expression was also observed following metamorphosis in which many tyrosinase-positive cells appear in the body of the developing juvenile. The results demonstrate that different urodele features can be uncoupled during the evolution of anural development. The development of a vestigial brain melanocyte also suggests that B. digonas evolved from a urodele ancestor rather than from another anural ascidian lacking a brain pigment cell.     

Regulation of site-specific recombination by the C-terminus of lambda integrase

Site-specific recombination catalyzed by bacteriophage λ integrase (Int) is essential for establishment and termination of the viral lysogenic life cycle. Int is the archetype of the tyrosine recombinase family whose members are responsible for DNA rearrangement in prokaryotes, eukaryotes and viruses. The mechanism regulating catalytic activity during recombination is incompletely understood. Studies of tyrosine recombinases bound to their target substrates suggest that the C-termini of the proteins are involved in protein–protein contacts that control the timing of DNA cleavage events during recombination. We investigated an Int truncation mutant (W350) that possesses enhanced topoisomerase activity but greater than 100-fold reduced recombination activity. Alanine scanning mutagenesis of the C-terminus indicates that two mutants, W350A and I353A, cannot perform site-specific recombination although their DNA binding, cleavage and ligation activities are at wild-type levels. Two other mutants, R346A and R348A, are deficient solely in the ability to cleave DNA. To explain these results, we have constructed a homology-threaded model of the Int structure using a Cre crystal structure. We propose that residues R346 and R348 are involved in orientation of the catalytic tyrosine that cleaves DNA, whereas W350 and I353 control and make intermolecular contacts with other Int proteins in the higher order recombination structures known as intasomes. These results suggest that Int and the other tyrosine recombinases have evolved regulatory contacts that coordinate site-specific recombination at the C-terminus.     

The Hsp90 Capacitor,Developmental Remodeling,and Evolution: The Robustness of Gene Networks and the Curious Evolvability of Metamorphosis

ABSTRACT

Genetic capacitors moderate expression of heritable variation and provide a novel mechanism for rapid evolution. The prototypic genetic capacitor, Hsp90, interfaces stress responses, developmental networks, trait thresholds and expression of wide-ranging morphological changes in Drosophila and other organisms. The Hsp90 capacitor hypothesis, that stress-sensitive storage and release of genetic variation through Hsp90 facilitates adaptive evolution in unpredictable environments, has been challenged by the belief that Hsp90-buffered variation is unconditionally deleterious. Here we review recent results supporting the Hsp90 capacitor hypothesis, highlighting the heritability, selectability, and potential evolvability of Hsp90-buffered traits. Despite a surprising bias toward morphological novelty and typically invariable quantitative traits, Hsp90-buffered changes are remarkably modular, and can be selected to high frequency independent of the expected negative side-effects or obvious correlated changes in other, unselected traits. Recent dissection of cryptic signal transduction variation involved in one Hsp90-buffered trait reveals potentially dozens of normally silent polymorphisms embedded in cell cycle, differentiation and growth control networks. Reduced function of Hsp90 substrates during environmental stress would destabilize robust developmental processes, relieve developmental constraints and plausibly enables genetic network remodeling by abundant cryptic alleles. We speculate that morphological transitions controlled by Hsp90 may fuel the incredible evolutionary lability of metazoan life-cycles.     

Transplantation of organic surface horizons of boreal soils into warmer regions alters microbiology but not the temperature sensitivity of decomposition

Changes in soil carbon, the largest terrestrial carbon pool, are critical for the global carbon cycle, atmospheric CO₂ levels and climate. Climate warming is predicted to be most pronounced in the northern regions and therefore the large soil carbon pool residing in boreal forests will be subject to larger global warming impact than soil carbon pools in the temperate or the tropical forest. A major uncertainty in current estimates of the terrestrial carbon balance is related to decomposition of soil organic matter (SOM). We hypothesized that when soils are exposed to warmer climate the structure of the ground vegetation will change much more rapidly than the dominant tree species. This change will alter the quality and amount of litter input to the soil and induce changes in microbial communities, thus possibly altering the temperature sensitivity of SOM decomposition. We transferred organic surface soil sections from the northern borders of the boreal forest zone to corresponding forest sites in the southern borders of the boreal forest zone and studied the effects of warmer climate after an adaptation period of 2 years. The results showed that initially ground vegetation and soil microbial community structure and community functions were different in northern and southern forest sites and that 2 years of exposure to warmer climate was long enough to cause changes in these ecological indicators. The rate of SOM decomposition was approximately equally sensitive to temperature irrespective of changes in vegetation or microbial communities in the studied forest sites. However, as temperature sensitivity of the decomposition increases with decreasing temperature regime, the proportional increase in the decomposition rate in northern latitudes could lead to significant carbon losses from the soils.