Individual-based modelling of Pinus sylvestris invasion after grazing abandonment in the French Massif Central

In the Chaîne des Puys, a mid-elevation volcanic mountain of the French Massif Central, Scots pine proves to be an invasive species colonizing abandoned lawns or heathlands, and forms in a few years monospecific natural forests. Most of the abandonment occurred 30 to 40 years ago and this process has now stopped. Thus, we lack data on the very first phase of tree colonization. We anticipate that a simulation tool could bring an appreciable help in (i) rebuilding the entire colonization process – including the initial phase – of pine settlement and (ii) answering questions about the origin of the narrow and unimodal distributions of age of pine stands we observed. In addition, such a simulator could help managers to forecast extension of Scots pine and to predict growth and evolution of present secondary forests. A spatially explicit individual-based model is presented. The model takes into account both space and time and includes growth of trees, seed production and seed dispersal, death and competition between individuals. The influence of the initial parameters are analyzed and elements of validation given. The model was then used to predict tree settlement and stand establishment using the initial conditions from a natural stand studied in the field whose characteristics before abandonment were known (number and age-distribution of trees, location of mother trees, time of abandonment). Three simulations were achieved by using the same initial conditions but following different scenarios for the recruitment process. The scenario of a fluctuating resistance of the resident vegetation (that controls the susceptibility of the environment to tree establishment) seemed as one of the most probable to explain the actual stand characteristics. We thus concluded that dynamic models could be improved by taking into account the resistance of the vegetation to colonization as a fluctuating parameter instead of a static and permanent attribute.     

Anti-mouse GPI-PLD antisera highlight structural differences between murine and bovine GPI-PLDs

Despite its well characterised biochemistry, the physiological role of glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) is unknown. Most of the previous studies investigating the distribution of GPI-PLD have focused on the human and bovine forms of the enzyme. Studies on mouse GPI-PLD are rare, partly due to the lack of a specific anti-mouse GPI-PLD antibody, but also due to the apparent low reactivity of existing antibodies to rodent GPI-PLDs. Here we describe the isolation of a mouse liver cDNA, the construction and expression of a recombinant enzyme and the generation of an affinity-purified rabbit anti-mouse GPI-PLD antiserum. The antibody shows good reactivity to partially purified murine and purified bovine GPI-PLD. In contrast, a rat anti-bovine GPI-PLD antibody shows no reactivity with the mouse enzyme and the two antibodies recognise different proteolytic fragments of the bovine enzyme. Comparison between the rodent, bovine and human enzymes indicates that small changes in the amino acid sequence of a short peptide in the mouse and bovine GPI-PLDs may contribute to the different reactivities of the two antisera. We discuss the implications of these results and stress the importance of antibody selection while investigating GPI-PLD in the mouse.     

Characterization of the Adhesive from Cuvierian Tubules of the Sea Cucumber <Emphasis Type="Italic">Holothuria forskali</Emphasis> (Echinodermata,Holothuroidea)

Abstract Sea cucumbers possess a peculiar specialized defense system: the so-called Cuvierian tubules. The system is mobilized when the animal is mechanically stimulated, resulting in the discharge of a few white filaments, the tubules. Their great adhesivity, combined with their high tensile strength, allows Cuvierian tubules to entangle and immobilize potential predators. The cellular origin and composition of the Cuvierian tubule adhesive were investigated in the species Holothuria forskali by studying prints left on the substratum after mechanical detachment of the tubule. Polyclonal antibodies raised against tubule print material were used to locate the origin of tubule print constituents in the tubules. Extensive immunoreactivity was detected in the secretory granules of mesothelial granular cells, suggesting that their secretions make up the bulk of the adhesive material. Tubule print material consists of 60% proteins and 40% carbohydrates, a composition that is unique among the adhesive secretions of marine invertebrates. Although it is highly insoluble, a small fraction of this material can be extracted using denaturing buffers. Electrophoretic analysis of the extracts revealed that it contains about 10 proteins with apparent molecular masses ranging from 17 to 220 kDa and with closely related amino acid compositions, rich in acidic and in small side-chain amino acids. The adhesive from the Cuvierian tubules of H. forskali shares these characteristics with many marine bioadhesives and structural biomaterials.     

Cytology and mendelism: early connection between Michael F. Guyer's contribution

This paper examines the contribution of the PhD dissertation of the American cytologist Michael F. Guyer (1874-1959) to the early establishment (in 1902-1903) of the parallel relationship between cytological chromosome behaviour in meiosis and Mendel's laws. Guyer's suggestions were among the first, which attempted to relate the variation observed in the offspring in hybridisation studies by a coherent cytological chromosome mechanism to meiosis before the rediscovery of Mendel's principles. This suggested for the first time that the chromosome mechanism involved a conjugation of maternal and paternal chromosomes during the synapsis followed by a segregation of parental chromosomes in the final germ cells and a random union of the final germ cells in the fertilization. It shows that this early suggestion was similar to William Austin Cannon's later chromosome proposal attempting to explain Mendel's principles and had some influence on Walter Sutton's cytological suggestion explaining correctly the behaviour of Mendel's particle by 1903.     

Nucleus-encoded,plastid-targeted glyceraldehyde-3-phosphate dehydrogenase (GAPDH) indicates a single origin for chromalveolate plastids

Plastids (the photosynthetic organelles of plants and algae) originated through endosymbiosis between a cyanobacterium and a eukaryote and subsequently spread to other eukaryotes by secondary endosymbioses between two eukaryotes. Mounting evidence favors a single origin for plastids of apicomplexans, cryptophytes, dinoflagellates, haptophytes, and heterokonts (together with their nonphotosynthetic relatives, termed chromalveolates), but so far, no single molecular marker has been described that supports this common origin. One piece of evidence comes from plastid-targeted glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which originated by a gene duplication of the cytosolic form. However, no plastid GAPDH has been characterized from haptophytes, leaving an important piece of the puzzle missing. We have sequenced genes encoding cytosolic, mitochondrion-targeted, and plastid-targeted GAPDH proteins from a number of haptophytes and heterokonts and found haptophyte homologs that branch within a strongly supported clade of chromalveolate plastid-targeted genes, being more closely related to an apicomplexan homolog than was expected. The evolution of plastid-targeted GAPDH supports red algal ancestry of apicomplexan plastids and raises a number of questions about the importance of plastid loss and the possibility of cryptic plastids in nonphotosynthetic lineages such as ciliates.     

A morphometric study of the external ear: age- and sex-related differences

The human ear is a defining feature of the face. Its subtle structures convey signs of age and sex that are unmistakable yet not easily defined. With analysis of normative cross-sectional data, this study explored anatomic and aesthetic differences in the ear between men and women, as well as changes in ear morphology with age. A total of 123 volunteers were randomly selected for this study. The cohort consisted of 89 women ages 19 to 65 years (median age, 42 years) and 34 men ages 18 to 61 years (median age, 35 years). The average total ear height across the entire cohort for both left and right ears was 6.30 cm, average lobular height was 1.88 cm, and average lobular width was 1.96 cm. As expected based on head size, significant sex-related differences were noted in the distance from the lateral palpebral commissure to both the helical root and insertion of the lobule. Measured distances in both vectors were approximately 4.6 percent longer in men than in women. Similarly, the height of the pinna was significantly larger in men than in women by approximately 6.5 percent. The average height and width of the lobule, however, were nearly identical in men and women. Analysis of age-related data showed a significant difference in the total ear height between the subpopulations; however, this difference was not significant after the lobular height was subtracted from total ear height, suggesting that the lobule was the only ear structure that changed significantly with age. In addition, lobular width decreased significantly with age. This study establishes normative data for ear morphology and clearly demonstrates the changes in earlobe morphology that occur with advancing age.     

Wnt signaling induces the myogenic specification of resident CD45+ adult stem cells during muscle regeneration

The observation that CD45(+) stem cells injected into the circulation participate in muscle regeneration raised the question of whether CD45(+) stem cells resident in muscle play a physiological role during regeneration. We found that CD45(+) cells cultured from uninjured muscle were uniformly nonmyogenic. However, CD45(+) cells purified from regenerating muscle readily gave rise to determined myoblasts. The number of CD45(+) cells in muscle rapidly expanded following injury, and a high proportion entered the cell cycle. Investigation of candidate pathways involved in embryonic myogenesis revealed that Wnt signaling was sufficient to induce the myogenic specification of muscle-derived CD45(+) stem cells. Moreover, injection of the Wnt antagonists sFRP2/3 into regenerating muscle markedly reduced CD45(+) stem cell proliferation and myogenic specification. Our data therefore suggest that mobilization of resident CD45(+) stem cells is an important factor in regeneration after injury and highlight the Wnt pathway as a potential therapeutic target for degenerative neuromuscular disease.