A targeted screen to detect recessive mutations that have quantitative effects

A key problem in mutagenesis research is developing methods that are sufficiently sensitive to detect a wide range of abnormal phenotypes. Major variants may be easy to identify, but it can be difficult to detect mutations that have subtle effects, particularly on a complex genetic background. This paper describes a targeted mutagenesis protocol with enough sensitivity to detect recessive mutations that have modest quantitative effects. The procedure relies on consomic inbred strains of mice-strains in which one homologous pair of chromosomes of an inbred strain has been replaced with the corresponding pair from a donor strain. Mice that carry the desired donor chromosome-the target of the screen-are mutagenized and bred back to the original recipient strain. The first-generation progeny (G1) that are heterozygous only for the donor chromosome are also bred back to the recipient strain. G2 animals that inherit nonrecombinant donor chromosomes are identified by genotyping. These animals may be backcrossed repeatedly to the recipient strain to dilute off-target mutations, but ultimately, nonrecombinant G2 animals are bred to each other. Their G3 progeny are genotyped at markers spaced at 5- to 10-cM intervals to identify mating pairs that are homozygous for shared segments of the mutagenized donor chromosome. Entire litters of G4 progeny that are homozygous for defined intervals are screened. By comparing phenotypes within and among litters of nearly isogenic G4 animals, mutations can be verified and simultaneously mapped with a precision of 5-10 cM. This method has the potential to consistently detect mutations that have effects on trait means of well under one standard deviation.

A new surgery for congenital nystagmus: effects of tenotomy on an achiasmatic canine and the role of extraocular proprioception

PURPOSE

Human eye-movement recordings have documented that surgical treatment of congenital nystagmus (CN) also produces a broadening of the null zone and changes in foveation that allow increased acuity. We used the achiasmatic Belgian sheepdog, a spontaneously occurring animal model of human CN and see-saw nystagmus (SSN), to test the hypothesis that changes induced by surgical interruption of the extraocular muscle afference without a change in muscle-length tension could damp both oscillations.

METHODS

An achiasmatic dog with CN and SSN underwent videotaping and infrared oculography in a sling apparatus and head restraints before and after all extraocular muscles (stage 1: 4 horizontal rectus muscles and stage 2 [4 months later]: 4 vertical rectus muscles and 4 oblique muscles) were surgically tenotomized and immediately reattached at their original insertions.

RESULTS

The dog had immediate and persistent visible, behavioral, and oculographic changes after each stage of this new procedure. These included damped CN and SSN, increased ability to maintain fixation, and increased periods of maintaining the target image on the area centralis over a broad range of gaze angles.

CONCLUSIONS

Severing and reattaching the tendons of the extraocular muscles affect some as-yet-unknown combination of central nervous system processes producing the above results. This new procedure may prove effective in patients with CN with either no null, a null at primary position, or a time-varying null (due to asymmetric, (a)periodic, alternating nystagmus). We infer from our results in an achiasmatic dog that tenotomy is the probable cause of the damping documented in human CN after Anderson-Kestenbaum procedures and should also damp CN and SSN in achiasma in humans. It may also prove useful in acquired nystagmus to reduce oscillopsia. The success of tenotomy in damping nystagmus in this animal suggests that the proprioceptive feedback loop has a more important role in ocular-motor control than has been appreciated. Finally, we propose a modified bimedial recession procedure, on the basis of the damping effects of tenotomy.

Mouse models for the analysis of myopia: an analysis of variation in eye size of adult mice

PURPOSE

To assess the relative importance of genetic and environmental factors that modulate eye growth, eyes, lenses, and retinas of 507 mice belonging to 50 strains were measured.

METHODS

Mice of both sexes and a wide range of ages (27 to 526 days) were perfused for electron microscopy and eyes, lenses, and retinas were dissected and measured. Our uniform fixation protocol was shown to cause a weight loss of 4 to 6%. Multiple linear regression methods were used to explore relations between eye and lens weight, retinal area, age, sex, body and brain weight, and retinal ganglion cell number.

RESULTS

The eye and lens of mice continue to grow long after sexual maturity is reached at 40 to 60 days of age. The pace of growth matches the logarithm of age. Despite their smaller bodies, females have eyes as large as those of males. The correlation of eye weight to brain weight is remarkably low (r = 0.19), whereas that to retinal area is high (r = 0.86). Surprisingly, the correlation between lens weight and the size of the posterior segment (eye minus lens weight) is only 0.5 to 0.6, and ratios of these parameters are highly variable. Heritability of all traits is between 25 to 50%.

CONCLUSIONS

The continued growth of eyes in adult mice provides an excellent system to test effects of genetic and molecular manipulations on the development and treatment of myopia. Heritability is sufficiently high to map genes that specifically modulate growth of different parts of the eye.

Eye1 and Eye2: gene loci that modulate eye size, lens weight, and retinal area in the mouse

PURPOSE

Vision is critically dependent on genetic factors that influence the rate and duration of eye growth. The genetic basis of variation in eye size in mice was explored, and genes that modulate eye weight, lens weight, and retinal area were mapped.

METHODS

Eyes of approximately 700 mice were weighed. Data were corrected by regression analysis to eliminate effects of sex, age, and body weight. Interval mapping was used to locate quantitative trait loci (QTLs) using recombinant inbred strains and F2 intercrosses between strains C57BL/6J and DBA/2J.

RESULTS

Major QTLs were discovered near the centromere of chromosome 5 (Eye1: genomewide P < 0.005) and on proximal chromosome 17 near the mast cell protease 6 gene (Eye2, P < 0.05). Both QTLs have significant effects on eye size, lens weight, and retinal area. The DBA/2J alleles at Eye1 and Eye2 are partially dominant and increase eye weight by as much as 1.0 mg. Analysis of 183 F2 progeny confirmed and refined the chromosomal assignments of both Eye1 and Eye2.

CONCLUSIONS

Eye1 and Eye2 are the first loci known to control normal variation in eye size in any mammal. The hepatic growth factor gene (Hgf), a potent mitogen expressed in the retina, pigment epithelium, and choroid, is a strong candidate for Eye1. The human homolog of Eye2 should map to chromosome 6p, 16q13.3, or 19q13, whereas that of Eye1 should map to 7q.

Evaluation of a personal air sampler for twenty-four hour collection of fine particles and semivolatile organics

The U.S. EPA has conducted an evaluation of a commercially available lightweight fine particle personal sampler for use in human exposure and biomarker studies involving 24-h collections of particulate matter, particle-bound organics such as polycyclic aromatic hydrocarbons (PAHs), and semivolatile organics (PAHs). Independent laboratory evaluation of the prototype design, intended to produce a 2.5-micron aerodynamic diameter cut-point at a flow between 1.5 and 1.7 lpm (liters per minute), indicated that at a challenge flow rate of 1.5 lpm, the sampler provided an aerodynamic cut-point (dp50) of only 1.7 microns. The variance between expected size selection resulted from the prototype's jet diameter dimension being inadvertently based upon a flow rate of 2.0 lpm rather than an intended 1.5-1.7 lpm. Other aerodynamic factors not presently accounted for may also have played an influence. Extrapolated cut-points for flow rates at 1 and 3 lpm for the prototype were determined to be 2.1 and 1.2 microns, respectively. Total losses attributed to unwanted particle retention within the sampler ranged from 10% for 0.91 micron size particles to essentially zero approaching diameters greater than 2.0 microns. The ambient concentration of particles (< 1.7 microns) needed for acceptable gravimetric filter measurements involving 24-h sample collection was determined to be 10 micrograms/m3. Investigation of the sampler to retain and recover PAHs using XAD-2 resin, often of importance in human exposure biomarker studies, indicated that corrected recoveries between 94% and 108% could be obtained for 16 priority pollutant PAH species. Overall evaluation of the personal monitor indicates that it has research utility due to its modular features and size but reconfiguration should be performed that would permit true PM2.5 size selection. The current configuration collects particles less than 2.5 microns at approximately 95% collection efficiency.

Prion domain initiation of amyloid formation in vitro from native Ure2p

The [URE3] non-Mendelian genetic element of Saccharomyces cerevisiae is an infectious protein (prion) form of Ure2p, a regulator of nitrogen catabolism. Here, synthetic Ure2p1-65 were shown to polymerize to form filaments 40 to 45 angstroms in diameter with more than 60 percent beta sheet. Ure2p1-65 specifically induced full-length native Ure2p to copolymerize under conditions where native Ure2p alone did not polymerize. Like Ure2p in extracts of [URE3] strains, these 180- to 220-angstrom-diameter filaments were protease resistant. The Ure2p1-65-Ure2p cofilaments could seed polymerization of native Ure2p to form thicker, less regular filaments. All filaments stained with Congo Red to produce the green birefringence typical of amyloid. This self-propagating amyloid formation can explain the properties of [URE3].

The PERIANTHIA gene encodes a bZIP protein involved in the determination of floral organ number in Arabidopsis thaliana

Mutations in the PERIANTHIA (PAN) gene of Arabidopsis thaliana specifically transform flowers from tetramerous to largely pentamerous, which is a characteristic of flowers of ancestral plants. We have cloned the PAN gene and here we show that it encodes a member of the basic region/leucine zipper class of transcription factors. Immunohistochemical analysis shows that the encoded protein is present in the apical meristem, the floral meristem, each whorl of organ primordia, and in ovule primordia during wild-type flower development. PAN expression occurs independently of genes affecting floral meristem identity, floral meristem size, or floral organ number. The near absence of a phenotype in transgenic plants overexpressing PAN and the contrast between the broad expression of PAN and the specificity of its mutant phenotype suggest that its activity may be regulated post-translationally or by the presence of partner proteins. Based on these results and on data reported previously, we propose models for the role of PAN in the evolution of flower pattern in the mustard family.

Genetic and physical characterization of a region of Arabidopsis chromosome 1 containing the CLAVATA1 gene

With the advance of Arabidopsis as a model system for understanding plant genetics, development and biochemistry, a detailed description of the genome is necessary. As such, focused projects are underway to map and sequence the Arabidopsis nuclear genome. We have characterized a region of chromosome 1, surrounding the CLAVATA1 (CLV1) locus. Three (RFLP) clones were mapped relative to clv1-1, and were used to construct an ca. 700 kb yeast artificial chromosome (YAC) contig. Three cosmids spanning the CLV1 locus were analyzed and ca. 24 kb of genomic DNA was sequenced, including a continuous stretch of 18 kb. In addition to generating clones in this region of chromosome 1, we have analyzed the size, spacing and organization of several contiguous genes.

Cell production and cell death in the generation of variation in neuron number

Retinal ganglion cell numbers in adult mice vary from 40,000 to 80, 000. Much of this variation and the prominent bimodality of strain averages are generated by allelic variants at the neuron number control 1 (Nnc1) locus on chromosome 11. The Nnc1 locus may modulate either ganglion cell production or the severity of ganglion cell death. Here we have determined what the relative contributions of these two processes are to variation in adult cell number by estimating total ganglion cell production in 10 strains of mice (A/J, BALB/cJ, BXD32, C57BL/6J, CAST/Ei, CARL/ChGo, CE/J, C3H/HeSnJ, DBA/2J, and LP/J). These strains have adult populations that range from 45,000 to 76,000 (data available at http://qtl.ml.org). We estimated cell production by counting ganglion cell axons after ganglion cell neurogenesis but before the onset of significant cell death. Total cell production ranges from 131,000 to 224,000, and most of the variation in adult ganglion cell number is explained by this significant variation in cell production. In contrast, the percentage of cell death is relatively uniform in most strains (approximately 69% cell loss). The exceptions are BXD32, a strain that has an extremely high adult cell population, and Mus caroli (CARL/ChGo), a wild southeast Asian species that is distantly related to laboratory strains. In BXD32 and M. caroli, approximately 62% of the population dies. Our analysis indicates that substitutions of single alleles at the Nnc1 locus are responsible for production differences of approximately 8000 ganglion cells.

Computational chemistry on commodity-type computers

A number of inexpensive computers were benchmarked with the ab initio program Gaussian 94, using both small standard test jobs and larger density functional (DFT) calculations. Several varieties of Pentium (x86) and Alpha CPU based systems were tested. Most of them were running under the open source code operating system Linux. They were compared with several workstations and supercomputers. The most powerful of today's commodity-type processors surpassed current supercomputers in speed. The choice of compilers and compilation options was often found to have a larger influence on job CPU times than details of the hardware. Especially on the x86 type machines, the jobs always ran faster the less memory (RAM) they were given. The fastest machine on a per-CPU basis was an Alpha/Linux system. For the DFT calculation, it was close to twice as fast as a Cray J90 supercomputer.

Genetic dissection of retinal development

Retinal development depends on complex interactions between products of thousands of genes and numerous cellular and environmental factors. We are using novel quantitative genetic methods to map and characterize genes that are responsible for the pervasive quantitative differences in the architecture of the eye and the retina. These genes, known as quantitative trait loci (QTLs), may also determine susceptibility to common eye diseases. To map QTLs that generate variation among normal individuals we have analyzed several traits in a wide variety of mice, including standard inbred strains, recombinant inbred strains, wild mice, F1 hybrids and intercross progeny. Here we review this approach and give three specific examples of how genes with well-defined functions in retinal development are being mapped and characterized.

The congenital and see-saw nystagmus in the prototypical achiasma of canines: comparison to the human achiasmatic prototype

We applied new methods for canine eye-movement recording to the study of achiasmatic mutant Belgian Sheepdogs, documenting their nystagmus waveforms and comparing them to humans with either congenital nystagmus (CN) alone or in conjunction with achiasma. A sling apparatus with head restraints and infrared reflection with either earth- or head-mounted sensors were used. Data were digitized for later evaluation. The horizontal nystagmus (1-6 Hz) was similar to that of human CN. Uniocular and disconjugate nystagmus and saccades were recorded. See-saw nystagmus (SSN), not normally seen with human CN, was present in all mutants (0.5-6 Hz) and in the one human achiasmat studied thus far. This pedigree is an animal model of CN and the SSN caused by achiasma or uniocular decussation. Given the finding of SSN in all mutant dogs and in a human, achiasma may be sufficient for the development of congenital SSN and, in human infants, SSN should alert the clinician to the possibility of either achiasma or uniocular decussation. Finally, the interplay of conjugacy and disconjugacy suggests independent ocular motor control of each eye with variable yoking in the dog.

Airborne exposures to PAH and PM2.5 particles for road paving workers applying conventional asphalt and crumb rubber modified asphalt

Personal exposure monitoring was conducted for road paving workers in three states. A research objective was to characterize and compare occupational exposures to fine respirable particles (< 2.5 microns) and particle-bound polycyclic aromatic hydrocarbons (PAHs) for road paving workers applying conventional (petroleum derived) asphalt and asphalt containing crumb rubber from shredded tires. Workers not exposed to asphalt fume were also included for comparison (to support the biomarker component of this study). The rubber content of the crumb rubber modified (CRM) asphalt at the three study sites was 12, 15, and 20%. A comparison of some specific job categories from two sites indicates greater potential carcinogenic PAH exposures during CRM asphalt work, however, the site with the greatest overall exposures did not indicate any differences for specific jobs. A statistical analysis of means for fine particle, pyrene and total carcinogenic PAH personal exposure shows, with two exceptions, there were no differences in exposures for these three measurement variables. One site shows significantly elevated pyrene exposure for CRM asphalt workers and another site similarly shows greater carcinogenic PAH exposure for CRM asphalt workers. Conventional and CRM asphalt worker airborne exposures to the PAH carcinogen marker, BaP, were very low with concentrations comparable to ambient air in many cities. However, this study demonstrates that asphalt road paving workers are exposed to elevated airborne concentrations of a group of unknown compounds that likely consist of the carcinogenic PAHs benz(a)anthracene, chrysene and methylated derivatives of both. The research described in this article has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

Plant homeobox genes: many functions stem from a common motif

Homeodomain-containing transcription factors play a variety of important roles in plant, animal, and fungal development. Mutational and evolutionary analysis is beginning to pinpoint specific roles of homeobox genes in plant meristem function. Even though many different plant homeobox genes encode very similar homeodomain sequences, overexpression studies suggest the existence of several levels of regulation that may specify the functions of the different proteins. Recent analysis of the maize Knotted1 gene and its orthologue in barley demonstrates some of these regulatory processes.

Natural variation in neuron number in mice is linked to a major quantitative trait locus on Chr 11

Common genetic polymorphisms-as opposed to rare mutations-generate almost all heritable differences in the size and structure of the CNS. Surprisingly, these normal variants have not previously been mapped or cloned in any vertebrate species. In a recent paper (), we suggested that much of the variation in retinal ganglion cell number in mice, and the striking bimodality of strain averages, are caused by one or two quantitative trait loci (QTLs). To test this idea, and to map genes linked to this variable and highly heritable quantitative trait, we have counted ganglion cells in 38 recombinant inbred strains (BXD and BXH) derived from parental strains that have high and low cell numbers. A genome-wide search using simple and composite interval-mapping techniques revealed a major QTL on chromosome (Chr) 11 in a 3 cM interval between Hoxb and Krt1 (LOD = 6.8; genome-wide p = 0.001) and possible subsidiary QTLs on Chr 2 and Chr 8. The Chr 11 locus, neuron number control 1 (Nnc1), accounts for one third of the genetic variance among BXH strains and more than half of that among BXD strains, but Nnc1 has no known effects on brain weight, eye weight, or total retinal cell number. Three strong candidate genes have been mapped previously to the same region as Nnc1. These genes-Rara, Thra, and Erbb2- encode receptors for retinoic acid, thyroxine, and neuregulin, respectively. Each receptor is expressed in the retina during development, and their ligands affect the proliferation or survival of retinal cells.

Three-dimensional structure of HIV-1 Rev protein filaments

The HIV-1 Rev protein facilitates the export of incompletely spliced and unspliced viral mRNAs from the nucleus. Rev polymerizes into two types of filaments in vitro. In the presence of RNA, Rev forms poorly ordered structures, while in the absence of RNA it polymerizes into regular hollow filaments. We have determined the helical structure of the latter filaments by analysis of cryo-electron micrographs, taking into account STEM measurements of mass-per-unit-length. They are made up of Rev dimers, arranged in a six-start helix, with 31 dimers in 2 turns, a pitch angle of 45 degrees, and an interstrand spacing of 3.8 nm. Three-dimensional reconstruction at 2.1 nm resolution reveals a smooth outer surface and a featured inner surface, with outer and inner diameters of approximately 14.8 and approximately 10.4 nm, respectively. The Rev dimer has a "top-hat" shape with a cylinder approximately 3.2 nm in diameter and approximately 2.2 nm high, pointing inward: the thinner rim areas pack together to form the filament wall. Raman spectroscopy shows polymerized Rev to have approximately 54% alpha-helix and 20-24% beta-sheet content. Electron microdiffraction of aligned filaments reveals a broad meridional reflection at approximately (0.51 nm(-1, suggesting approximate alignment of the alpha-helices with the filament axis. Based on these data, a molecular model for the Rev filament is proposed.

A possible role for kinase-associated protein phosphatase in the Arabidopsis CLAVATA1 signaling pathway

Continuous growth and development in plants are accomplished by meristems, groups of undifferentiated cells that persist as stem cells and initiate organs. While the structures of the apical and floral meristems in dicotyledonous plants have been well described, little is known about the underlying molecular mechanisms controlling cell proliferation and differentiation in these structures. We have shown previously that the CLAVATA1 (CLV1) gene in Arabidopsis encodes a receptor kinase-like protein that controls the size of the apical and floral meristems. Here, we show that KAPP, a gene encoding a kinase-associated protein phosphatase, is expressed in apical and young floral meristems, along with CLV1. Overexpression of KAPP mimics the clv1 mutant phenotype. Furthermore, CLV1 has kinase activity: it phosphorylates both itself and KAPP. Finally, KAPP binds and dephosphorylates CLV1. We present a model where KAPP functions as a negative regulator of the CLAVATA1 signal transduction pathway.

Decreased retinal ganglion cell number and misdirected axon growth associated with fissure defects in Bst/+ mutant mice

PURPOSE

The autosomal semidominant mutation Bst (belly spot and tail) is often associated with small and atrophic optic nerves in adult mice and shares several important attributes with heritable optic nerve atrophy in humans. In this article, the authors present adult and developmental studies on the retinal phenotype in Bst/+ mice.

METHODS

Retinal ganglion cells in adult Bst/+ mice were labeled retrogradely with horseradish peroxidase injected into the right optic tract. Labeled ganglion cells were mapped in whole-mounted retinas ipsilateral and contralateral to the injection site. The number of axons in optic nerves of these and other cases were quantified using an electron microscopic method. Eyes of neonatal, embryonic day 15 (E15), and embryonic day 12 (E12) Bst/+ mutants were examined histologically to understand the etiology of the retinal phenotype.

RESULTS

Approximately 60% of adult Bst/+ mice have deficient direct pupillary light responses. This neurologic phenotype is associated with a reduction in the number of retinal ganglion cells from the wild-type average of 67,000 to less than 20,000 in Bst/+ mutants. Ganglion cells with crossed projections are more severely affected than those with uncrossed projections. Histologic analysis of eyes from E12 mice reveals a delayed closure of the optic fissure. Despite this abnormality, other ocular structures appear relatively normal. However, some E15 mutants exhibit marked disorganization of the retinal neuroepithelium, and ganglion cell axons are found between pigmented and neural retina. At birth, optic nerves of affected mice are smaller than those of wild-type mice, ectopic axons are found within the eyes, and the ganglion cell layer contains many dying cells.

CONCLUSIONS

The expression of the retinal phenotype in Bst/+ mutants is highly variable-ranging from a complete absence of ganglion cells to numbers comparable to that in wild-type mice. The reduction in ganglion cell number in affected adult Bst/+ mice is attributable to the failure of ganglion cell axons to reach the optic nerve head early in development. Delayed fusion of the fissure is consistently associated with the Bst/+ genotype and probably contributes to the failure of ganglion cell axons to grow out of the eye.

The CLAVATA1 gene encodes a putative receptor kinase that controls shoot and floral meristem size in Arabidopsis

The shoot apical meristem is responsible for above-ground organ initiation in higher plants, accomplishing continuous organogenesis by maintaining a pool of undifferentiated cells and directing descendant cells toward organ formation. Normally, proliferation and differentiation are balanced, so that the structure and size of the shoot meristem is maintained. However, Arabidopsis plants homozygous for mutations at the CLAVATA1 (CLV1) locus accumulate excess undifferentiated cells. We describe the molecular cloning and expression pattern of the CLV1 gene. It encodes a putative receptor kinase, suggesting a role in signal transduction. The extracellular domain is composed of 21 tandem leucine-rich repeats that resemble leucine-rich repeats found in animal hormone receptors. We provide evidence that CLV1 expression in the inflorescence is specifically associated with meristematic activity.

The CLAVATA1 gene encodes a putative receptor kinase that controls shoot and floral meristem size in Arabidopsis

The shoot apical meristem is responsible for above-ground organ initiation in higher plants, accomplishing continuous organogenesis by maintaining a pool of undifferentiated cells and directing descendant cells toward organ formation. Normally, proliferation and differentiation are balanced, so that the structure and size of the shoot meristem is maintained. However, Arabidopsis plants homozygous for mutations at the CLAVATA1 (CLV1) locus accumulate excess undifferentiated cells. We describe the molecular cloning and expression pattern of the CLV1 gene. It encodes a putative receptor kinase, suggesting a role in signal transduction. The extracellular domain is composed of 21 tandem leucine-rich repeats that resemble leucine-rich repeats found in animal hormone receptors. We provide evidence that CLV1 expression in the inflorescence is specifically associated with meristematic activity.

Genetic and environmental control of variation in retinal ganglion cell number in mice

How much of the remarkable variation in neuron number within a species is generated by genetic differences, and how much is generated by environmental factors? We address this problem for a single population of neurons in the mouse CNS. Retinal ganglion cells of inbred and outbred strains, wild species and subspecies, and F1 hybrids were studied using an unbiased electron microscopic method with known technical reliability. Ganglion cell numbers among diverse types of mice are highly variable, ranging from 32,000 to 87,000. The distribution of all cases (n = 252) is close to normal, with a mean of 58,500 and an SD of 7800. Genetic factors are most important in controlling this variation; 76% of the variance is heritable and up to 90% is attributable to genetic factors in a broad sense. Strain averages have an unanticipated bimodal distribution, with distinct peaks at 55,500 and 63,500 cells. Three pairs of closely related strains have ganglion cell populations that differ by > 20% (10,000 cells). These findings indicate that different alleles at one or two genes have major effects on normal variation in ganglion cell number. Nongenetic factors are still appreciable and account for a coefficient of variation that averages approximately 3.6% within inbred strains and isogenic F1 hybrids. Age- and sex-related differences in neuron number are negligible. Variation within isogenic strains appears to be generated mainly by developmental noise.

Arbitrary primer PCR of dog DNA with estimates of average heterozygosity

Arbitrary primer polymerase chain reaction (AP-PCR) detected anonymous DNA polymorphisms between individual representatives of seven breeds of dogs, between members of a single breed, and between members of a single family of dogs. Short arbitrary sequence PCR primers and promoter/protein motif sequence primers typically amplified 15-30 bands ranging from 200-2000 bp in length. The average heterozygosity of 10 line bred Belgian sheepdogs (H = 0.024 +/- 0.011, mean +/- 95% CI) was significantly lower than that of a panel of unrelated beagles (H = 0.057 +/- 0.018, mean +/- 95% CI, P < .01). The average heterozygosity of a seven-breed panel was intermediate between the two (H = 0.043 +/- 0.011, mean +/- 95% CI) and not significantly different than either panel. One motif sequence PCR primer pair yielded products that strongly differentiated between Belgian sheepdogs, beagles, and members of five other breeds. AP-PCR could be used to generate DNA fingerprints that distinguish between dog breeds, as well as to provide markers in this sparsely mapped genome.

Changes in mutagenicity during crude oil degradation by fungi

Two fungal strains, Cunninghamella elegans and Penicillium zonatum, that grow with crude oil as a sole carbon source were exposed to three crude oils that exhibit a range of mutagenic activity. At regular time intervals following fungal incubation with the various crude oils, extracts were tested for the presence of mutagenic activity using the spiral Salmonella assay. When the most mutagenic of the oils, Pennsylvania crude oil, was degraded by C. elegans or by P. zonatum, its mutagenicity was significantly reduced; corresponding uninoculated (weathered) controls of Pennsylvania crude remained mutagenic. West Texas Sour crude oil, a moderately mutagenic oil, exhibited little change in mutagenicity when incubated with either C. elegans or P. zonatum. Swanson River Field crude oil from Cook Inlet, Alaska is a slightly mutagenic oil that became more mutagenic when incubated with C. elegans; weathered controls of this oil showed little change in mutagenicity. Mycelial mat weights measured during growth on crude oils increased corresponding to the biodegradation of about 25% of the crude oil.