In vivo desensitization of a high affinity PGF2 alpha receptor in the ovine corpus luteum.

The corpus luteum (CL) of the sheep exhibits a differential sensitivity to PGF2 alpha in vivo in terms of an increase in oxytocin (OT) secretion and a decrease in progesterone secretion, pointing to the presence in vivo of both high and low affinity receptors for PGF2 alpha. The presence of the high affinity PGF2 alpha receptor was assessed by monitoring the secretion rate of OT from the ovine CL in response to subluteolytic infusions of PGF2 alpha. Rapid desensitization to PGF2 alpha occurred after only one hour of infusion, while a minimum rest period of six hours was required to restore sensitivity. The possibility that these findings could be explained by the depletion and resynthesis of OT was excluded by demonstrating an increase in OT secretion rate with supra-physiological levels of PGF2 alpha two hours after desensitization. Collectively, these results indicate the presence of a high affinity receptor for PGF2 alpha in the ovine CL which exhibits desensitization and recovery in vivo. The temporal nature of the desensitization and recovery of the high affinity PGF2 alpha receptor controlling luteal OT secretion may contribute to the pulsatile nature of PGF2 alpha release from the ovine uterus.     

Where buffalo and cattle meet: modelling interspecific contact risk using cumulative resistant kernels

African buffalo the primary source of foot and mouth disease (FMD) infection for livestock in South Africa. Predicting the spatial drivers and patterns of buffalo–cattle contact risk is crucial for developing effective FMD mitigation strategies. Therefore, the goal of this study was to predict fine‐scale, seasonal contact risk between cattle and buffaloes straying into communal lands adjacent to Kruger National Park. This study provides the first application of the cumulative resistant kernel method to calculate contact risk between two species. We built resistance surfaces from resource utilization models of buffalo and cattle and calculated the intersection of resistant kernels of the two species. This revealed that the contact risk is influenced by seasonality, water sources and fence strength, and the magnitude of contact risk is largely driven by buffalo and cattle dispersal abilities. The probability of contact was higher in the dry season, with hotspots along a main river and the weakest parts of the perimeter fence. In the wet season, contact risk was more diffuse and less concentrated along the main river and near settlements. The new approach of intersecting cumulative resistant kernels of two species can produce quantitative predictive maps of animals’ contact risk and help identify potential hotspots of disease transmission.     

Molecular evolution of mitochondrial 12S RNA and cytochrome b sequences in the pantherine lineage of Felidae

DNA sequence comparisons of two mitochondrial DNA genes were used to infer phylogenetic relationships among 17 Felidae species, notably 15 in the previously described pantherine lineage. The polymerase chain reaction (PCR) was used to generate sequences of 358 base pairs of the mitochondrial 12S RNA gene and 289 base pairs of the cytochrome b protein coding gene. DNA sequences were compared within and between 17 felid and five nonfelid carnivore species. Evolutionary trees were constructed using phenetic, cladistic, and maximum likelihood algorithms. The combined results suggested several phylogenetic relationships including (1) the recognition of a recently evolved monophyletic genus Panthera consisting of Panthera leo, P. pardus, P. onca, P. uncia, P. tigris, and Neofelis nebulosa; (2) the recent common ancestry of Acinonyx jubatus, the African cheetah, and Puma concolor, the American puma; and (3) two golden cat species, Profelis temmincki and Profelis aurata, are not sister species, and the latter is strongly associated with Caracal caracal. These data add to the growing database of vertebrate mtDNA sequences and, given the relatively recent divergence among the felids represented here (1-10 Myr), allow 12S and cytochrome b sequence evolution to be addressed over a time scale different from those addressed in most work on vertebrate mtDNA.      

Molecular Genetics of Crassulacean Acid Metabolism

Most higher plants assimilate atmospheric CO2 through the C3 pathway of photosynthesis using ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). However, when CO2 availability is reduced by environmental stress conditions, the incomplete discrimination of CO2 over O2 by Rubisco leads to increased photorespiration, a process that reduces the efficiency of C3 photosynthesis. To overcome the wasteful process of photorespiration, approximately 10% of higher plant species have evolved two alternate strategies for photosynthetic CO2 assimilation, C4 photosynthesis and Crassulacean acid metabolism. Both of these biochemical pathways employ a "CO2 pump" to elevate intracellular CO2 concentrations in the vicinity of Rubisco, suppressing photorespiration and therefore improving the competitiveness of these plants under conditions of high light intensity, high temperature, or low water availability. This CO2 pump consists of a primary carboxylating enzyme, phosphoenolpyruvate carboxylase. In C4 plants, this CO2-concentrating mechanism is achieved by the coordination of two carboxylating reactions that are spatially separated into mesophyll and bundle-sheath cell types (for review, see R.T. Furbank, W.C. Taylor [1995] Plant Cell 7: 797-807;M.S.B. Ku, Y. Kano-Murakami, M. Matsuoka [1996] Plant Physiol 111: 949-957). In contrast, Crassulacean acid metabolism plants perform both carboxylation reactions within one cell type, but the two reactions are separated in time. Both pathways involve cell-specific changes in the expression of many genes that are not present in C3 plants.     

Sea urchin Hox genes: insights into the ancestral Hox cluster

We describe the Hox cluster in the radially symmetric sea urchin and compare our findings to what is known from clusters in bilaterally symmetric animals. Several Hox genes from the direct-developing sea urchin Heliocidaris erythrogramma are described. CHEF gel analysis shows that the Hox genes are clustered on a < or = 300 kilobase (kb) fragment of DNA, and only a single cluster is present, as in lower chordates and other nonvertebrate metazoans. Phylogenetic analyses of sea urchin, amphioxus, Drosophila, and selected vertebrate Hox genes confirm that the H. erythrogramma genes, and others previously cloned from other sea urchins, belong to anterior, central, and posterior groups. Despite their radial body plan and lack of cephalization, echinoderms retain at least one of the anterior group Hox genes, an orthologue of Hox3. The structure of the echinoderm Hox cluster suggests that the ancestral deuterostome had a Hox cluster more similar to the current chordate cluster than was expected Sea urchins have at least three Abd-B type genes, suggesting that Abd-B expansion began before the radiation of deuterostomes.