Scanning electron microscope study of Candida albicans invasion of cultured human cervical epithelial cells

The invasion of monolayer cultures of epithelial cells from the human uterine cervix by clinical isolates of Candida albicans was observed. Blastospores settle on the epithelial cells and produce germ tubes within 2 h. Hyphae penetrate the epithelial cell walls and destroy the cells, weaving in and out of the cytoplasm. No phagocytosis of yeast cells by epithelial cells was seen.     

Heterozygous expression of insulin-dependent diabetes mellitus (IDDM) determinants in the HLA system.

HLA phenotypes of cases with insulin-dependent diabetes mellitus (IDDM) and identity by descent of HLA haplotypes in affected sib-pairs support an intermediate model in which morbid risk is increased by one HLA-linked IDDM determinant, and greatly increased by two determinants, which may be qualitatively different in DR3 and DR4 haplotypes. Linkage analysis allowing for gametic disequilibrium reveals no recombination in pedigrees with a DR3/DR4 propositus, but spurious recombination in the remaining pedigrees. This evidence favors interaction of unlinked IDDM determinants to produce affection in a small proportion of heterozygotes for an HLA-linked determinant. Partition of data by HLA type of the propositus (ideally by DR and the complement types jointly) is a powerful method to resolve etiological heterogeneity for HLA-associated diseases.     

Malignant Neoplasms of the Nasopharynx

A mass in the neck, facial pain and cranial nerve palsies are the most common presenting symptoms of malignant tumours of the nasopharynx. Surgery is limited to biopsy for histological diagnosis. External irradiation is the treatment of choice, both for the primary lesion and the regional and distant metastases. Illustrative case histories are presented in detail. Experience over a 20-year period demonstrates that a 20% five-year survival rate has been obtained.     

Comparison of theα-globin gene cluster structure in Perissodactyla

Summary To investigate molecular evolution in a mammalian order with a comprehensive fossil record, we have constructed-globin-like gene cluster maps for members of the order Perissodactyla. Although the arrangement of genes is the same in the five Equidae examined, the tapir and rhinoceros differ from each other and the horse in the position and number of their genes, but not in the arrangement of their and genes. In contrast to morphological work, a dendrogram derived from restriction site maps associates the tapir with the horse rather than with the rhinoceros; however, this phylogeny is not statistically significant. Among the Equidae,Equus caballus emerges as an outgroup, in agreement with data from other disciplines.     

Allozyme variation and differentiation in African and Indian rhinoceroses

We studied variation at 25 to 31 allozymic loci in African and Asian rhinoceroses. Four taxa in three genera were examined: African Ceratotherium simum simum (northern white rhinoceros), C. s. cottoni (southern white rhinoceros), Diceros bicornis (black rhinoceros), and Rhinoceros unicornis (Indian rhinoceros). Extremely small amounts of intraspecific variation were observed in sample sizes of 2 to 10 presumably unrelated individuals per taxon: P = .00-.10, H = 0.00-0.02. We examined demographic bottlenecks and sampling errors as possible reasons for the low levels of detectable variation. The very small intraspecific genetic distance (D = 0.005) between the two living white rhinoceros subspecies is far less than the distance that has been reported for other mammal subspecies. The mean D value of 0.32 +/- 0.11 between the two African genera was also less than expected given the divergence time of greater than 7 million years suggested by the fossil record. Rhinoceroses may be evolving more slowly at the structural gene loci than are some other mammal groups. The estimate of D = 1.05 +/- 0.24 for the African-Indian split supports this idea, as the lineage diverged at least 26 million years ago. Our results contribute to the currently available scientific information on which management decisions aimed toward saving endangered rhinoceroses should be based.     

Targeted snRNP depletion reveals an additional role for mammalian U1 snRNP in spliceosome assembly

HeLa cell nuclear splicing extracts have been prepared that are specifically and efficiently depleted of U1, U2, or U4/U6 snRNPs by antisense affinity chromatography using biotinylated 2'-OMe RNA oligonucleotides. Removal of each snRNP particle prevents pre-mRNA splicing but arrests spliceosome formation at different stages of assembly. Mixing extracts depleted for different snRNP particles restores formation of functional splicing complexes. Specific binding of factors to the 3' splice site region is still detected in snRNP-depleted extracts. Depletion of U1 snRNP impairs stable binding of U2 snRNP to the pre-mRNA branch site. This role of U1 snRNP in promoting stable preslicing complex formation is independent of the U1 snRNA-5' splice site interaction.     

An Experimental Test of the Rhizopine Concept in Rhizobium meliloti

In some Rhizobium-legume symbioses, compounds known as rhizopines are synthesized by bacteroids and subsequently catabolized by free-living cells of the producing strain. It has been suggested than rhizopines act as proprietary growth substrates and enhance the competitive ability of the producing strain in its interactions with the diverse microbial community found within the rhizosphere. Wild-type, rhizopine-producing Rhizobium meliloti L5-30 and mutant L5-30 strains deficient for either rhizopine synthesis or catabolism were inoculated onto lucerne host plants in competition experiments. These experiments demonstrated that no apparent advantage resulted from the ability to synthesize a rhizopine, whereas the ability to catabolize rhizopine provided a clear advantage when an organism was in competition with a strain without this ability. The results suggest that when an organism is in competition with a catabolism-deficient mutant, the ability to catabolize rhizopine results in enhanced rates of nodulation. The results of the experiments were not consistent with the hypothesis that the sole role of rhizopines is to act as proprietary growth substrates for the free-living population of the producing strain.