CHARACTERIZATION OF THE Na+K+-ATPase IN ISOLATED BOVINE ARTICULAR CHONDROCYTES; MOLECULAR EVIDENCE FOR MULTIPLE α AND β ISOFORMS

We have used isoform-specific antibodies against the Na⁺K⁺-ATPase αα1, α2 and α3) and ββ1 and β2) subunit isoforms in order to establish their specific localization in isolated bovine articular chondrocytes. Immunoblotting confirmed the presence of the α1 and α3 isoforms, although α1 expression was significantly greater than α3 as assessed by immunofluorescence confocal laser scanning microscopy and PCR. A similar approach revealed the presence of the β1 and β2 isoforms in chondrocytes, although β2 immunostaining on the plasma membrane was more punctate than β1 which in contrast predominated in a subcellular compartment. The plasma membrane abundance of the Na⁺K⁺-ATPase was found to be sensitive to the extracellular ionic concentration and long-term elevation of extracellular Na⁺concentration significantly upregulated Na⁺K⁺-ATPase density as measured by specific³H-ouabain binding. Our observations suggest that the expression of α3 and β2 is not restricted to excitable tissues as previously reported. The physiological relevance of α3 expression in chondrocytes may be related to its low affinity for intracellular Na⁺in an extracellular environment where Na⁺concentration is unusually high (260–350mm) compared to other cell types (140mm). Glycoproteins and their branched carbohydrates have been implicated in cell recognition events, thus the β2 subunit glycoprotein may allow the chondrocyte to detect changes in its extracellular environment by physically interacting with components of the cellular cytoskeleton and matrix macromolecules.     

Hierarchical structure of mitochondrial DNA gene flow among humpback whales Megaptera novaeangliae, world-wide

The genetic structure of humpback whale populations and subpopulation divisions is described by restriction fragment length analysis of the mitochondrial (mt) DNA from samples of 230 whales collected by biopsy darting in 11 seasonal habitats representing six subpopulations, or 'stocks', world-wide. The hierarchical structure of mtDNA haplotype diversity among population subdivisions is described using the analysis of molecular variance (AMOVA) procedure, the analysis of gene identity, and the genealogical relationship of haplotypes as constructed by parsimony analysis and distance clustering. These analyses revealed: (i) significant partitioning of world-wide genetic variation among oceanic populations, among subpopulations or 'stocks' within oceanic populations and among seasonal habitats within stocks; (ii) fixed categorical segregation of haplotypes on the south-eastern Alaska and central California feeding grounds of the North Pacific; (iii) support for the division of the North Pacific population into a central stock which feeds in Alaska and winters in Hawaii, and an eastern or 'American' stock which feeds along the coast of California and winters near Mexico; (iv) evidence of genetic heterogeneity within the Gulf of Maine feeding grounds and among the sampled feeding and breeding grounds of the western North Atlantic; and (v) support for the historical division between the Group IV (Western Australia) and Group V (eastern Australia, New Zealand and Tonga) stocks in the Southern Oceans. Overall, our results demonstrate a striking degree of genetic structure both within and between oceanic populations of humpback whales, despite the nearly unlimited migratory potential of this species. We suggest that the humpback whale is a suitable demographic and genetic model for the management of less tractable species of baleen whales and for the general study of gene flow among long-lived, mobile vertebrates in the marine ecosystem.     

Soil [N] modulates soil C cycling in CO2‐fumigated tree stands: a meta‐analysis

Under elevated atmospheric CO₂ concentrations, soil carbon (C) inputs are typically enhanced, suggesting larger soil C sequestration potential. However, soil C losses also increase and progressive nitrogen (N) limitation to plant growth may reduce the CO₂ effect on soil C inputs with time. We compiled a data set from 131 manipulation experiments, and used meta‐analysis to test the hypotheses that: (1) elevated atmospheric CO₂ stimulates soil C inputs more than C losses, resulting in increasing soil C stocks; and (2) that these responses are modulated by N. Our results confirm that elevated CO₂ induces a C allocation shift towards below‐ground biomass compartments. However, the increased soil C inputs were offset by increased heterotrophic respiration (Rh), such that soil C content was not affected by elevated CO₂. Soil N concentration strongly interacted with CO₂ fumigation: the effect of elevated CO₂ on fine root biomass and –production and on microbial activity increased with increasing soil N concentration, while the effect on soil C content decreased with increasing soil N concentration. These results suggest that both plant growth and microbial activity responses to elevated CO₂ are modulated by N availability, and that it is essential to account for soil N concentration in C cycling analyses.     

An Oocyte-Specific Antigen and Its Possible Role in the Organization of the Ovarian Follicle of the Rat

An oocyte-specific antigen was detected by an antiserum produced in isogenic Lewis rats. The antigen was sensitive to trypsin treatment. Dissociation-reorganization experiments in vitro , using ovarian cells demonstrated that the antigen is required for the interaction of germ cells and somatic cells. A physiologic role is suggested for this differentiation antigen in follicular morphogenesis and ovarian function.     

Neumann’s Warbler Hemitesia neumanni (Sylvioidea): the sole African member of a Palaeotropic Miocene avifauna

We present molecular evidence that Neumann’s Warbler Hemitesia neumanni is deeply nested within the Cettiidae. The species’ distribution in the Albertine Rift of East Africa is intriguing, as the family Cettiidae is principally an Asian radiation. This disjunct distribution could be a result of colonization of Africa by long‐distance dispersal, or the Cettiidae may at some point in the past have had a much larger geographical distribution that also covered parts of Africa.