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R W Beeman

Publications and source records attributed to R W Beeman.

33 records · Page 2Linked to original sources
PubMed1994

The population dynamics of maternal-effect selfish genes.

We use population genetic methods to describe the expected population dynamics of the selfish-gene chromosomal factor, Medea (maternal-effect dominant embryonic arrest), recently discovered in flour beetles, genus Tribolium. In the absence of deleterious effects on gross fecundity, Medea factors spread to fixation for all degrees of maternal-effect lethality greater than zero and the rate of spread is proportional to the strength of the maternal-effect. The rate of spread when rare is very slow, on the order of the frequency squared p2, but this can be accelerated to order p when there is density regulation at the level of families as is known to occur for some genetic strains of flour beetles. When there are general deleterious effects of Medea on fecundity, affecting all offspring genotypes in addition to the genotype-specific maternal effect, then a stable interior polymorphism is possible. The location of the interior equilibrium and the probability of loss or fixation are sensitive to the degree of dominance of these fecundity effects.

Animals↗
PubMed1994

Genetic control of early embryogenesis in the red flour beetle, Tribolium castaneum.

The power of genetic analysis possible with the fruit fly, Drosophila melanogaster, has yielded a detailed understanding of pattern formation controlled by homeotic and segmentation genes in early embryogenesis. We are studying the genetic regulation of embryogenesis in the red flour beetle, Tribolium castaneum. The dynamic process of germ rudiment formation and sequential segmentation exhibited by Tribolium provides a context different than Drosophila within which to assess the function of homeotic and segmentation gene homologs. Our analyses of the genes in the HOM-C suggest many similarities in structure and function with the well-characterized Drosophila genes. Abdominal resembles its Drosophila homolog abdominal-A in functioning to establish segmental identities in the abdomen, such that in each case mutations result in homeotic transformations to PS6. Although the anterior functional boundary of abdominal-A homologs is precisely conserved, the domain within which Abdominal is important extends more posterior than that of abdominal-A. The final expression pattern of the segmentation gene engrailed in Tribolium is identical to Drosophila, suggesting that these homologs are involved in a conserved developmental process. However, as expected the development of that pattern is different; engrailed stripes anticipate the formation of each new segment as they appear sequentially in the elongating germ band. Although the grasshopper even-skipped and fushi tarazu homologs are not apparently important in segmentation, the expression patterns of the Tribolium homologs strongly suggest that they have gained a role in segmentation in the lineage leading to beetles and flies. Nevertheless, differences between Tribolium and Drosophila in the dynamics of even-skipped expression and the fushi tarazu mutant phenotype indicate divergence in the regulation and roles of these genes.

Animals↗
PubMed1993

Structure and function of the homeotic gene complex (HOM-C) in the beetle, Tribolium castaneum.

The powerful combination of genetic, developmental and molecular approaches possible with the fruit fly, Drosophila melanogaster, has led to a profound understanding of the genetic control of early developmental events. However, Drosophila is a highly specialized long germ insect, and the mechanisms controlling its early development may not be typical of insects or Arthropods in general. The beetle, Tribolium castaneum, offers a similar opportunity to integrate high resolution genetic analysis with the developmental/molecular approaches currently used in other organisms. Early results document significant differences between insect orders in the functions of genes responsible for establishing developmental commitments.

Animals↗
PubMed1993

The Tribolium homeotic gene Abdominal is homologous to abdominal-A of the Drosophila bithorax complex.

The Abdominal gene is a member of the single homeotic complex of the beetle, Tribolium castaneum. An integrated developmental genetic and molecular analysis shows that Abdominal is homologous to the abdominal-A gene of the bithorax complex of Drosophila. abdominal-A mutant embryos display strong homeotic transformations of the anterior abdomen (parasegments 7-9) to PS6, whereas developmental commitments in the posterior abdomen depend primarily on Abdominal-B. In beetle embryos lacking Abdominal function, parasegments throughout the abdomen are transformed to PS6. This observation demonstrates the general functional significance of parasegmental expression among insects and shows that the control of determinative decisions in the posterior abdomen by homeotic selector genes has undergone considerable evolutionary modification.

Amino Acid Sequence↗
PubMed1992

Maternal-effect selfish genes in flour beetles.

A previously unknown class of dominant, maternal-effect lethal M factors was found to be widespread in natural populations of the flour beetle, Tribolium castaneum, collected on several continents. Such factors are integrated into the host chromosomes at variable locations and show the remarkable property of self-selection by maternal-effect lethality to all hatchlings that do not inherit a copy of the factor itself. Offspring are rescued by either paternally or maternally inherited copies. The M-bearing chromosome is thereby perpetuated at the expense of its non-M homolog. M factors that map to different regions of the genome do not rescue one another's maternal-effect lethality. Factors expressing these properties are predicted to spread in a population, even in the absence of any additional selective advantage. Similar factors also occur in the related species T. confusum.

Animals↗
PubMed1991

A deficiency of the homeotic complex of the beetle Tribolium.

In Drosophila, the establishment of regional commitments along most of the anterior/posterior axis of the developing embryo depends on two clusters of homeotic genes: the Antennapedia complex (ANT-C) and the bithorax complex (BX-C). The red flour beetle has a single complex (HOM-C) representing the homologues of the ANT-C and BX-C in juxtaposition. Beetles trans-heterozygous for two particular HOM-C mutations spontaneously generate a large deficiency, presumably by an exchange within the common region of two overlapping inversions. Genetic and molecular results indicate that this deficiency spans at least the interval between the Deformed and abdominal-A homologues. In deficiency homozygous embryos, all gnathal, thoracic and abdominal segments develop antennal appendages, suggesting that a gene(s) has been deleted that acts to distinguish trunk from head. There is no evidence that beetles have a homologue of the segmentation gene fushi tarazu of similar genomic location and function. On the basis of the genetic tractability, convenient genome size and organization of Tribolium, and its relatively long phylogenetic divergence from Drosophila (>300 million years), we have integrated developmental genetic and molecular analyses of the HOM-C. We isolated about 70 mutations in the complex representing at least six complementation groups. The homeotic phenotypes of adults and lethal embryos lead us to believe that these beetle genes are homologous with the Drosophila genes indicated in Fig. 1 (see text).

Animals↗
PubMed1989

Genetic analysis of the homeotic gene complex (HOM-C) in the beetle Tribolium castaneum.

Our laboratories have undertaken both genetic and molecular studies of the homeotic gene complex (HOM-C) of the beetle Tribolium castaneum, and this paper discusses results from our genetic analyses. We describe here the adult phenotypes and complementation behavior of over 50 new mutations. Many of these homeotic phenotypes resemble those of Drosophila melanogaster, but few precisely parallel the segmental transformations seen in this fly. Analysis of putative loss-of-function mutations affecting the head and thorax suggests that the maxillopedia and Cephalothorax genes most closely resemble proboscipedia and Sex combs reduced of Drosophila. In the abdomen, putative loss-of-function alleles of Abdominal affect a domain corresponding to those of the combined abdominal-A and Abdominal-B genes of Drosophila. In contrast to the situation in flies, Abdominal loss-of-function variants in Tribolium cause anteriorward transformations in A3-A5a, but posteriorward transformations in A5p-A7. The implications of the differences in developmental strategies evolved in Tribolium vs Drosophila are discussed.

Abdomen↗
PubMed1980

Esophageal perforation following use of the esophageal obturator airway.

Four cases of esophageal rupture associated with the use of the esophageal obturator airway are presented and added to the fifteen cases already in the literature. The incidence of this complication may be greater than previously suspected since a systematic search for this complication has not been made in cardiac arrest patients. The mechanism of rupture of the occluded esophagus may be similar to that seen in postemetic rupture. Endotracheal intubation remains the procedure of choice in airway control of cardiac arrest patients, although the modified esophageal obturator airway with gastric tube may prevent the occurrence of esophageal rupture by allowing decompression of the esophagus.

Aged↗
PubMed1976

Biochemical and physiological effects of chlordimeform.

Chlordimeform is a relatively new acaricide/insecticide, whose mode of action we have investigated. It appears to interfere with amine-mediated control of nervous and endocrine systems in a variety of ways. Specifically, chlordimeform causes a build-up of the amines 5-hydroxytryptamine and to a lesser extent norepinephrine in the rat brain in vivo, antagonizes the in vivo action of reserpine in the rat (reserpine depletes amine stores in the CNS), inhibits monoamine oxidase from rat liver in vitro, and causes hypotension in rabbits. In the American cockroach it directly stimulates the heart in situ, acts synergistically with tryptamine in vivo, inhibits amine-N-acetyltransferase from cockroach head in vitro, causes accumulation of indolamines in cockroaches in vivo, and blocks the stimulation of adenylate cyclase by octopamine in the cockroach CNS in situ. It also inhibits tryptamine metabolism in whole mites in vitro.

Amidines↗
PubMedDate not supplied

Assisted suicide of a selfish gene.

Medea (M) factors and the hybrid incompatibility factor (H) are involved in two incompatibility systems in flour beetles that were previously thought to be independent. M factors are a novel class of selfish genes that act by maternal lethality to nonself. The H factor causes the death of hybrids with a paternally derived H gene and previously uncharacterized maternal cofactors. We now find that M factors exhibit their selfish behavior only in the absence of the H factor. Furthermore, we show that the previously uncharacterized maternal cofactors required for H-associated hybrid inviability are identical to M factors. We propose that incompatibility between H strains and M strains is due to suppression by the H factor of the self-rescuing activity of the lethal M genes. This interaction has the effect of converting M elements from selfish into self-destructive or "suicidal" genes. M factors are globally widespread, but are conspicuously absent from India, the only country where the H factor is known to occur. Such a mechanism could prevent the spread of selfish M elements by establishing an absolute barrier to hybridization in the boundary between M and non-M zones.

Animals↗
PubMedDate not supplied

Chromosome extraction and revision of linkage group 2 in Tribolium castaneum.

We used a balancer chromosome to recover ethylmethanesulfonate-induced recessive mutations in a targeted region of the genome of the red flour beetle (Tribolium castaneum) by the technique of chromosome extraction. The experiments reported herein constitute the first successful application of this powerful technique in the order Coleoptera. Using the balancer chromosome maxillopedia-Dachs3 (mxpDch-3), we recovered seven recessive visible variants representing seven distinct loci and several dozen recessive lethal variants representing at least five distinct loci after screening 1,607 EMS-mutagenized chromosomes. A subset of the mxpDch-3-extracted mutations were positioned on the map of the second linkage group by a series of two-, three-, and four-point crosses. The orientation of the homeotic gene complex (HOM-C) on this linkage group was also determined. With the advent of better and more varied balancer chromosomes and the concomitant improvement of chromosome extraction procedures for genetic analysis of T. castaneum, saturation mutagenesis of targeted regions of the genome is now feasible in this species.

Animals↗