Cytologic features of islet-cell tumors

Although a number of reports have demonstrated the accuracy of fine needle aspiration (FNA) in the diagnosis of nonendocrine pancreatic carcinomas, the cytomorphology of islet-cell tumors (pancreatic endocrine tumors) is not well defined. This paper describes the cytologic features of three histologically confirmed cases of islet-cell tumors. The three tumors occurred in one man and two women, who were 63, 64 and 70 years of age, respectively. Each patient underwent FNA of pancreatic mass with computed body tomography guidance. The aspirates contained large numbers of tumor cells in two cases and a smaller number in one case. The cells, distributed singly and in small groups, were small and round or polygonal, with scant to more often abundant, dense or granular cytoplasm. The nuclei were often located eccentrically and were round to oval, with smooth nuclear borders and finely stippled chromatin. Many nuclei contained a single nucleolus. Multinucleated cells were present and generally contained two or three nuclei. Although the diagnosis of islet-cell tumors in fine needle aspirates is difficult, the cytomorphologic features of these tumors are sufficiently distinctive to suggest the diagnosis, especially when a relatively monomorphic population composed predominantly of single cells is present.     

Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications

Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of individuals representing 54 species of frogs, two species of salamanders, a caecilian, and a lungfish. Eight of these sites were present in all species examined, and two were found in all but one species. Alignment of these conserved restriction sites revealed, among anuran 28S rRNA genes, five regions of major length variation that correspond to four of 12 previously identified divergent domains of this gene. One of the divergent domains (DD8) consists of two regions of length variation separated by a short segment that is conserved at least throughout tetrapods. Most of the insertions, deletions, and restriction-site variations identified in the 28S gene will require sequence-level analysis for a detailed reconstruction of their history. However, an insertion in DD9 that is coextensive with frogs in the suborder Neobatrachia, a BstEII site that is limited to representatives of two leptodactylid subfamilies, and a deletion in DD10 that is found only in three ranoid genera are probably synapomorphies.      

Selenocysteine's mechanism of incorporation and evolution revealed in cDNAs of three glutathione peroxidases

The nonsense codon, UGA, has for the first time recently been shown to encode selenocysteine in two proteins, mouse glutathione peroxidase (GSH-Px) (EC 1.11.1.9) and bacterial formate dehydrogenase. A co-translational rather than post-translational selenium-incorporation mechanism has been implicated. Furthermore, high expression levels of GSH-Px have suggested that suppression of termination is efficient and specific. We have isolated and characterized pituitary, kidney and placenta cDNAs for bovine, human and mouse GSH-Px respectively. It is demonstrated that this novel suppression event occurs in diverse tissues, in at least three mammalian species and at the translational step. Surprisingly, GSH-Px is shown to be extramitochondrially encoded, indicating a cytosolic suppression event rather than one utilizing the mitochondria's well-documented extended codon-reading ability. Sequence analysis reveals that a simple proximal contextual pattern responsible for readthrough does not exist. Analysis of predicted secondary structures of mRNAs, however, has revealed a conformation which may be unique to selenocysteine proteins and may prove useful as a tool for artificial incorporation of selenocysteines. A human intron for GSH-Px from an unspliced mRNA has been isolated whose position indicates an ancient, divergent evolutionary relationship with thioredoxin-S2, rather than an independent convergent one.     

Decreased incidence of mycorrhizal root tips associated with soil heavy-metal enrichment

Mycorrhizal incidence was studied at two forested locations in south-central Virgina. At each location, one site with soil naturally enriched in copper, lead and zinc was designated as mineralized, and an adjacent site, with significantly lower levels of these metals, was used as a control. A total of 223 soil samples were collected during the summer of 1984 and assayed for active mycorrhizal tips. A reduced active mycorrhizal root tip count was found in those samples collected from the mineralized sites at both locations (P≤0.001).     

A continuous noncontact method for measuring in situ vascular diameter with a video camera

A new, continuous, on-line, video diameter-measuring technique, utilizing a video camera mounted on the sidearm of a stereo microscope, is described. Vessel diameter is derived from changes in the video output signal of the camera or a video recorder when the vessel of interest is displayed horizontally on a monitor and well contrasted with its background. A comparator threshold is set on the filtered video output signal and generates an output pulse that is used to gate horizontal video sync pulses to a digital counter-timer. The number of pulses counted for each video field (no. of horizontal video lines) is proportional to the vessel diameter. The video-derived diameter is calibrated using known standards and correlates well with sonomicrometer-derived diameters of the carotid artery and jugular vein during increasing pressure ramps (r greater than 0.999). The diameter update rate is 60 Hz, and the resolution of the system is one horizontal video line, independent of the vessel size. With suitable magnification and contrast both arteries and veins as small as 200 micron have been measured using this system.     

Identification of a CA repeat at the TCRA locus using yeast artificial chromosomes: a general method for generating highly polymorphic markers at chosen loci.

The creation of a comprehensive genetic map in human has been limited by the lack of highly polymorphic markers spaced evenly throughout the human genome. We have utilized yeast artificial chromosomes (YAC) containing large human DNA inserts to help identify highly polymorphic (CA)n repeats at a chosen locus. The DNA of a YAC containing the locus was subcloned in M13 vectors, and the recombinants were screened at high stringency to detect preferentially long (CA)n repeats (n greater than 20). These repeats, which are the most likely to be highly polymorphic, were then studied to confirm both the level of polymorphism and their precise genetic location. This strategy has permitted the identification of a new, highly polymorphic CA repeat (77% heterozygosity) at the T cell receptor alpha chain (TCRA) locus on chromosome 14q. It provides a powerful marker for assessing the role of this locus in the susceptibility to autoimmune and infectious diseases. This approach should permit the development of highly polymorphic markers at any targeted locus and rapidly improve the current human genetic map.