Genetic counselor training: a review and considerations for the future.

The first training program for genetic counselors began in 1969. Since then a number of other programs have been developed and more than 650 individuals have graduated from these programs. This article reviews the development and current status of training opportunities for genetic counselors. Twelve programs that currently grant a master's-level degree in genetic counseling are reviewed. Other areas, such as certification and licensure, that reflect genetic counseling training or such issues of professional growth as continuing education and career advances are addressed.     

Separation of large DNA restriction fragments on a size-exclusion column by a nonideal mechanism

Double-strand DNA (dsDNA) restriction fragments were chromatographed on the DuPont Bioseries GF-250 column. Two anomolous chromatographic properties were observed. (1) A triphasic dependence of retention on dsDNA chain length was observed. Small DNA fragments (less than 500 base pairs) displayed typical size exclusion, intermediate size DNA (800-5000 base pairs) eluted in the void volume, and larger DNA fragments were increasingly retained. (2) The void volume for nucleic acids was less than that for large polypeptides. The retention of moderately large DNA fragments increased linearly as the square root of the chain length over the range 5.5 to 50 kilobase pairs (ca. 3-30 X 10(6) Mr). A number of eluant manipulations were carried out in order to examine the mechanism by which the larger DNA fragments were being retained and separated. Evidence was not obtained to support either ion exchange or reverse phase as the retention mechanism. The usefulness of such a column for molecular biological manipulations is illustrated by the rapid isolation of homogeneous viral DNA fragments resected from their cloning vectors with restriction endonucleases.     

All nod genes of Rhizobium meliloti are involved in alfalfa nodulation by exo mutants.

Nodulation of alfalfa by exoB mutants of Rhizobium meliloti occurred without root hair curling or infection thread formation. nod exoB double mutants had the same nodulation deficiency as single nod mutants. Therefore, all the known nod genes are involved in nodule induction by exoB mutants, which apparently occurs via intercellular invasion.     

Amikacin disrupts the cell envelope of Pseudomonas aeruginosa ATCC 9027

Amikacin, an aminoglycoside known to inhibit protein synthesis, was found to perturb the outer membrane of a sensitive Pseudomonas aeruginosa strain (ATCC 9027). This perturbation was monitored using electron microscopy and biochemical analyses. Following exposure to 20 micrograms amikacin/mL for 15 min, the outer membrane of exponentially growing cells lost 15% of its protein, 18% of its lipopolysaccharide, and 18% of its phosphate. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed that the whole spectrum of outer membrane protein and lipopolysaccharide was affected. Similarly, atomic absorption spectrophotometry revealed that magnesium and calcium were also lost. When cells were treated with amikacin, electron microscopy of negative stains showed a substantial increase in outer membrane blebbing. Freeze fractures revealed changes in membrane fracture pattern and particle distribution, and thin sections revealed a sequential disruption of the cell envelope beginning at the outer membrane and ending at the plasma membrane. This study supports the proposal that aminoglycoside antibiotics cross the outer membrane of Pseudomonas aeruginosa by displacing metal cations necessary to stabilize the organic constituents of the membrane. Their removal results in loss of the outer membrane and the formation of transient small holes which permit the antibiotic access to the cytoplasmic membrane where it is transported into the cytoplasm.     

Selective association and transport of Campylobacter jejuni through M cells of rabbit Peyer's patches

M cells in the Peyer's patches may facilitate transport of pathogens such as Campylobacter jejuni from the intestine. We evaluated this hypothesis by using electron microscopy to examine Peyer's patches in ligated adult rabbit ileal loops inoculated with 5-mL suspensions of 10(9) cfu/mL of Campylobacter jejuni. Peyer's patches taken at intervals from 15 min to 2 h after inoculation of loops in anaesthetized rabbits provided evidence that Campylobacter jejuni selectively adhered to M cells as opposed to absorptive epithelial cells and was transported, apparently intact, into the M cell follicle. Although intercellular organisms were seen within the follicle, many others were phagocytosed by lymphoid cells. The proximity of the lymphatic and blood circulatory systems to the M cell follicle makes this a probable route for systemic spread of Campylobacter jejuni.     

Improved procedure for the isolation of a double-strand-specific ribonuclease and its application to structural analysis of various 5S rRNAs and tRNAs

An improved method for the isolation of a double-strand-specific RNase from snake venom is presented. This RNase, called CSV, was used to cleave yeast tRNAPhe and tRNA2Glu and tRNAfMet from Escherichia coli. In addition these RNAs and E. coli tRNAPhe were examined with the single-strand-specific nuclease S1. The results are discussed in terms of the specificity of CSV RNase and the structure of tRNAs. S1 nuclease digestions at increasing temperatures allowed the melting of tertiary and secondary structure to be monitored. 5S rRNA from E. coli, Thermoplasma acidophilum and the chloroplasts of Spinacia oleracea were digested with CSV and S1. The information these results give on the secondary-structural differences between different classes of 5S rRNA are discussed. Supporting evidence is found for tertiary interactions between hairpin loop c and internal loop d of eubacterial 5S rRNA.     

Changes in the cell wall of Clostridium species following passage in animals

Morphological changes in clostridial isolates after animal passage with other flora in mixed infections were studied by utilizing a subcutaneous abscess model in mice. We used 26 isolates of 7 clostridial species, and one isolate each of Bacteroides fragilis and Klebsiella pneumoniae. Abscesses were induced by all 7 Clostridium perfringens and 3 Clostridium butyricum isolates and by some of the other isolates. A thick granular wall prior to animal inoculation was shown only in C. perfringens, C. butyricum, and C. difficile. This structure was observed in other clostridia only following their animal passage alone or when co-inoculated with K. pneumoniae or B. fragilis.     

Rotavirus-associated diarrhea in a commercial rabbitry

An epizootic of diarrheal disease occurred in a commercial specific-pathogen-free rabbitry, and was characterized by sudden onset, rapid spread, and high morbidity and mortality among sucklings. Affected rabbits rapidly became dehydrated and most died within two days of the onset of diarrhea. Eight of these rabbits were necropsied. Five had blunted and fused small intestinal villi with attenuated villous enterocytes. A rotavirus was isolated from four rabbits, and five survivors of affected litters had strong antibody responses to rotavirus.     

Defect in expression of heat-shock proteins at high temperature in xthA mutants.

Escherichia coli mutants lacking exonuclease III (xthA) are defective in the induction of heat-shock proteins upon severe heat-shock treatment (upshift from 30 to 50 degrees C) but not mild heat-shock treatment (upshift from 30 to 42 degrees C). We show that this defect is due to the xthA mutation by complementation. Furthermore, increasing the gene dosage of xthA+ prolongs the synthesis of heat shock proteins seen after a shift to 42 degrees C. Increasing the gene dosage of htpR+ partially suppresses the defect of xthA mutants in the synthesis of heat-shock proteins at 50 degrees C. When an xthA strain was incubated at 42 degrees C before a shift to 50 degrees C, it was then able to carry out the synthesis of heat-shock proteins at 50 degrees C.     

Thermoregulation, metabolism, and stages of sleep in cold-exposed men

Four naked men, selected for their ability to sleep in the cold, were exposed to an ambient temperature (Ta) of 21 degrees C for five consecutive nights. Electrophysiological stages of sleep, O2 consumption (VO2), and skin (Tsk), rectal (Tre), and tympanic (Tty) temperatures were recorded. Compared with five nights at a thermoneutral Ta of 29 degrees C, cold induced increased wakefulness and decreased stage 2 sleep, without significantly affecting other stages. Tre and Tty declined during each condition. The decrease in Tre was greater at 21 degrees C than at 29 degrees C, whereas Tty did not differ significantly between conditions. Increases in Tty following REM sleep onset at 21 degrees C were negatively correlated with absolute Tty. VO2 and forehead Tsk also increased during REM sleep at both TaS, whereas Tsk of the limb extremities declined at 21 degrees C. Unsuppressed REM sleep in association with peripheral vasoconstriction and increased Tty and VO2 in cold-exposed humans, do not signify an inhibition of thermoregulation during this sleep stage as has been observed in other mammals.