Latitudinal variation in population structure of wintering Pacific Black Brant

ABSTRACT.   Latitudinal variation in population structure during the winter has been reported in many migratory birds, but has been documented in few species of waterfowl. Variation in environmental and social conditions at wintering sites can potentially influence the population dynamics of differential migrants. We examined latitudinal variation in sex and age classes of wintering Pacific Black Brant ( Branta bernicla nigricans ). Brant are distributed along a wide latitudinal gradient from Alaska to Mexico during the winter. Accordingly, migration distances for brant using different wintering locations are highly variable and winter settlement patterns are likely associated with a spatially variable food resource. We used resightings of brant banded in southwestern Alaska to examine sex and age ratios of birds wintering at Boundary Bay in British Columbia, and at San Quintin Bay, Ojo de Liebre Lagoon, and San Ignacio Lagoon in Baja California from 1998 to 2000. Sex ratios were similar among wintering locations for adults and were consistent with the mating strategy of geese. The distribution of juveniles varied among wintering areas, with greater proportions of juveniles observed at northern (San Quintin Bay and Ojo de Liebre Lagoon) than at southern (San Ignacio Lagoon) locations in Baja California. We suggest that age-related variation in the winter distribution of Pacific Black Brant is mediated by variation in productivity among individuals at different wintering locations and by social interactions among wintering family groups.     

GT to AT transition at a splice donor site causes skipping of the preceding exon in phenylketonuria.

Classical Phenylketonuria (PKU) is an autosomal recessive human genetic disorder caused by a deficiency of hepatic phenylalanine hydroxylase (PAH). We isolated several mutant PAH cDNA clones from a PKU carrier individual and showed that they contained an internal 116 base pair deletion, corresponding precisely to exon 12 of the human chromosomal PAH gene. The deletion causes the synthesis of a truncated protein lacking the C-terminal 52 amino acids. Gene transfer and expression studies using the mutant PAH cDNA indicated that the deletion abolishes PAH activity in the cell as a result of protein instability. To determine the molecular basis of the deletion, the mutant chromosomal PAH gene was isolated from this individual and shown to contain a GT-- greater than AT substitution at the 5' splice donor site of intron 12. Thus, the consequence of the splice donor site mutation in the human liver is the skipping of the preceding exon during RNA splicing.     

Defective repair of DNA single- and double-strand breaks in the bleomycin- and X-ray-sensitive Chinese hamster ovary cell mutant, BLM-2

Using filter elution techniques, we have measured the level of induced single- and double-strand DNA breaks and the rate of strand break rejoining following exposure of two Chinese hamster ovary (CHO) cell mutants to bleomycin or neocarzinostatin. These mutants, designated BLM-1 and BLM-2, were isolated on the basis of hypersensitivity to bleomycin and are cross-sensitive to a range of other free radical-generating agents, but exhibit enhanced resistance to neocarzinostatin. A 1-h exposure to equimolar doses of bleomycin induces a similar level of DNA strand breaks in parental CHO-K1 and mutant BLM-1 cells, but a consistently higher level is accumulated by BLM-2 cells. The rate of rejoining of bleomycin-induced single- and double-strand DNA breaks is slower in BLM-2 cells than in CHO-K1 cells. BLM-1 cells show normal strand break repair kinetics. The level of single- and double-strand breaks induced by neocarzinostatin is lower in both BLM-1 and BLM-2 cells than in CHO-K1 cells. The rate of repair of neocarzinostatin-induced strand breaks is normal in BLM-1 cells but retarded somewhat in BLM-2 cells. Thus, there is a correlation between the level of drug-induced DNA damage in BLM-2 cells and the bleomycin-sensitive, neocarzinostatin resistant phenotype of this mutant. Strand breaks induced by both of these agents are also repaired with reduced efficiency by BLM-2 cells. The neocarzinostatin resistance of BLM-1 cells appears to be a consequence of a reduced accumulation of DNA damage. However, the bleomycin-sensitive phenotype of BLM-1 cells does not apparently correlate with any alteration in DNA strand break induction or repair, as analysed by filter elution techniques, suggesting an alternative mechanism of cell killing.     

The effect of water and nitrogen amendments on photosynthesis,leaf demography,and resource-use efficiency in Larrea tridentata,a desert evergreen shrub

Summary In the Chihuahuan Desert of southern New Mexico, both water and nitrogen limit the primary productivity of Larrea tridentata, a xerophytic evergreen shrub. Net photosynthesis was positively correlated to leaf N, but only in plants that received supplemental water. Nutrient-use efficiency, defined as photosynthetic carbon gain per unit N invested in leaf tissue, declined with increasing leaf N. However, water-use efficiency, defined as the ratio of photosynthesis to transpiration, increased with increasing leaf N, and thus these two measures of resource-use efficiency were inversely correlated. Resorption efficiency was not significantly altered over the nutrient gradient, nor was it affected by irrigation treatments. Leaf longevity decreased significantly with fertilization although the absolute magnitude of this decrease was fairly small, in part due to a large background of insect-induced mortality. Age-specific gas exchange measurements support the hypothesis that leaf aging represents a redistribution of resources, rather than actual deterioration or declining resource-use efficiency.     

An epitope on C4 β light (L) chains detected by human anti-Rg; its relationship with β chain polymorphism and MHC associations

Two out of ten Rg-specific antisera tested contain a third antibody specific for the β chain of C4. Analysis of the β chains of 66 unrelated individuals by sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed that the epitope detected is located exclusively on the light (L) β chain. A strong, but incomplete, association between the β chain epitope and the expression of the Rg: 2 determinant on the α chain of the same protein was also observed. While H (heavy) and L β chains were not associated with a particular C4 isotype, previously unrecorded associations of β chain polymorphism with theDR locus have been established.     

Hensen's node,but not other biological signallers,can induce supernumerary digits in the developing chick limb bud

Summary The purpose of this study was to determine whether the organizer regions of early avian and amphibian embryos could induce supernumerary (SN) wing structures to develop when they were grafted to a slit in the anterior side of stage 19–23 chick wing buds. Supernumerary digits developed in 43% of the wings that received anterior grafts of Hensen's node from stage 4–6 quail or chick embryos; in addition, 16% of the wings had rods of SN cartilage, but not recognizable SN digits. The grafted quail tissue did not contribute to the SN structures. When tissue anterior or lateral to Hensen's node or lateral pieces of the area pellucida caudal to Hensen's node were grafted to anterior slits, the wings usually developed normally. No SN structures developed when Hensen's nodes were grafted to posterior slits in chick wing buds. Wings developed normally when pieces of the dorsal lip of the blastopore from stage 10–11.5 frog (Xenopus laevis and Rana pipiens) embryos were grafted to anterior slits. No SN digits developed when other tissues that have limb-inducing activity in adult urodele amphibians [chick otic vesicle, frog (Rana pipiens) lung and kidney] or that can act as heteroinductors in neural induction (rat kidney, lung, submaxillary gland and urinary bladder; mouse liver and submaxillary gland) were grafted to anterior slits in chick wing buds. SN digits also failed to develop following preaxial grafts of chick optic vesicles. These results suggest that although the anteroposterior polarity of the chick wing bud can be influenced by factors other than the ZPA (e.g., Hensen's node, retinoids), the wing is not so labile that it can respond to a wide variety of inductively-active tissues.     

Genetic tagging of tumor cells with retrovirus vectors: clonal analysis of tumor growth and metastasis in vivo.

Retrovirus vector infection was used to introduce large numbers of unique genetic markers into tumor cell populations for the purpose of analyzing comparative changes in the clonal composition of metastatic versus that of nonmetastatic tumors during their progressive growth in vivo. The cell lines used were SP1, a nonmetastatic, aneuploid mouse mammary adenocarcinoma, and SP1HU9L, a metastatic variant of SP1. Cells were infected with delta e delta pMoTN, a replication-defective retrovirus vector which possesses the dominant selectable neo gene and crippled long terminal repeats. G418r colonies were obtained at a frequency of 4 x 10(-3). Southern blot analysis of a number of clones provided evidence of random and heritable integration of one or two copies of the proviral DNA. Clonal evolution of primary tumor growth and the nature of lineage relationships among spontaneous metastases and primary tumors were analyzed by subcutaneously injecting 10(5) cells from a pooled mixture of 3.6 x 10(2) G418r SP1HU9L or 10(4) G418r SP1 colonies into syngeneic CBA/J mice. The most striking finding was the relative clonal homogeneity of advanced primary tumors; they invariably consisted of a small number (less than 10) of distinct clones despite the fact that hundreds or thousands of uniquely marked clones had been injected. In the case of the metastatic SP1HU9L cells, the nature of these "dominant" clones varied from one tumor to another. Analysis of a number of lung metastases revealed that a proportion of them were derived from dominant primary tumor clones and were composed of one, and sometimes two, distinct progenitors. In some animals, all the lung metastases were derived from a common progenitor clone, whereas in others, each metastatic nodule had a different progenitor. The results show the following. (i) Retrovirus vector infection can be used to introduce large numbers of unique and stable clonal markers into tumor cell populations. (ii) The progeny of a very limited number of clones dominate in advanced primary tumors. (iii) Mammary carcinoma metastases are of mono- or biclonal origin. The significance of the results is discussed.