Cloning of glycoprotein IIIa cDNA from human erythroleukemia cells and localization of the gene to chromosome 17

Platelet aggregation requires the binding of adhesive proteins such as fibrinogen to the heterodimer of membrane glycoproteins IIb (GPIIb) and IIIa (GPIIIa). Human erythroleukemia (HEL) cells synthesize both GPIIb and GPIIIa. Using poly(A+) RNA purified from HEL cells, we constructed a cDNA library in the lambda gt10 phage vector. This library was screened with a 38mer oligonucleotide derived from a platelet GPIIIa peptide, and three overlapping cDNAs were isolated. The three inserts encompassed 3.5 kilobases (kb), including the entire coding region of mature GPIIIa (2,286 basepairs, bp) and 1.3 kb of 3' untranslated sequence. All 222 residues determined directly from platelet GPIIIa tryptic peptides exactly matched the HEL cell-deduced amino acid sequence. The HEL cell sequence matched a previously reported endothelial cell cDNA sequence except for eight nucleotides. Five of these nucleotide differences were silent changes consistent with genetic polymorphisms. The other three differences resulted in changes in the deduced amino acid sequence of GPIIIa; reexamination of the endothelial cell cDNA sequence in these three areas revealed that it is actually identical to the HEL cell sequence. The virtual identity of the endothelial and HEL cell cDNA sequences provides direct evidence that GPIIIa is a subunit common to cell-adhesion receptors present in more than one cell type. We localized the gene for GPIIIa to chromosome 17, the same chromosome to which we had previously mapped the gene for GPIIb.     

Evidence for balancing selection operating at the het-c heterokaryon incompatibility locus in a group of filamentous fungi

In filamentous fungi, het loci (for heterokaryon incompatibility) are believed to regulate self/nonself-recognition during vegetative growth. As filamentous fungi grow, hyphal fusion occurs within an individual colony to form a network. Hyphal fusion can occur also between different individuals to form a heterokaryon, in which genetically distinct nuclei occupy a common cytoplasm. However, heterokaryotic cells are viable only if the individuals involved have identical alleles at all het loci. One het locus, het-c, has been characterized at the molecular level in Neurospora crassa and encodes a glycine-rich protein. In an effort to understand the role of this locus in filamentous fungi, we chose to study its evolution by analyzing het-c sequence variability in species within Neurospora and related genera. We determined that the het-c locus was polymorphic in a field population of N. crassa with close to equal frequency of each of the three allelic types. Different species and even genera within the Sordariaceae shared het-c polymorphisms, indicating that these polymorphisms originated in an ancestral species. Finally, an analysis of the het-c specificity region shows a high occurrence of nonsynonymous substitution. The persistence of allelic lineages, the nearly equal allelic distribution within populations, and the high frequency of nonsynonymous substitutions in the het-c specificity region suggest that balancing selection has operated to maintain allelic diversity at het-c. Het-c shares this particular evolutionary characteristic of departing from neutrality with other self/nonself-recognition systems such as major histocompatibility complex loci in mammals and the S (self-incompatibility) locus in angiosperms.     

Pseudoaneurysm: a complication of faulty technique in femoral arterial puncture

Pseudoaneurysm is a well-documented but rare complication of retrograde femoral arterial puncture. We present six patients in whom pseudoaneurysm complicated this procedure. The pseudoaneurysm arose from the superficial femoral artery in five patients and from the profunda femoris artery in one. An arteriovenous fistula also arose from the superficial femoral artery in one patient. In no patient did the pseudoaneurysm arise from the common femoral artery. Two mechanisms are postulated as to why pseudoaneurysms rarely complicate puncture of the common femoral artery.     

Validation of a prediction rule to maximize curative (R0) resection of early-stage pancreatic adenocarcinoma

Background:

The surgeon''s contribution to patients with localized pancreatic adenocarcinoma (PAC) is a margin negative (R0) resection. We hypothesized that a prediction rule based on pre-operative imaging would maximize the R0 resection rate while reducing non-therapeutic intervention.

Methods:

The prediction rule was developed using computed tomography (CT) and endoscopic ultrasound (EUS) data from 65 patients with biopsy-proven PAC who underwent attempted resection. The rule classified patients as low or high risk for non-R0 outcome and was validated in 78 subsequent patients.

Results:

Model variables were: any evidence of vascular involvement on CT; EUS stage and EUS size dichotomized at 2.6 cm. In the validation cohort, 77% underwent resection and 58% achieved R0 status. If only patients in the low-risk group underwent surgery, the prediction rule would have increased the resection rate to 92% and the R0 rate to 73%. The R0 rate was 40% higher in low-risk compared with high-risk patients (P < 0.001). High risk was associated with a 67% rate of non-curative surgery (unresectable disease and metastases).

Conclusion:

The prediction rule identified patients most likely to benefit from resection for PAC using pre-operative CT and EUS findings. Model predictions would have increased the R0 rate and reduced non-therapeutic interventions.