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W B Wood

Publications and source records attributed to W B Wood.

At least 19 recordsLinked to original sources
PubMed1995

Microscopic age changes in the human occipital bone.

The value of histological examination of the human occipital bone for estimation of age-at-death was assessed. Undecalcified sections of occipital bone from eighteen male Caucasian subjects between the ages of 21 and 70 years were prepared for analysis using polarized light microscopy. The fractional volumes of primary osteons, secondary osteons, osteon fragments, and lamellar bone in both the outer and inner cortical tables were determined. It was found that with increasing age there is a decrease in the fractional volume of primary osteons and a significant decrease in the fractional volume of lamellar bone. The fractional volume of secondary osteons was not found to change significantly with age, while the fractional volume of osteon fragments significantly increases. The microscopic results reflect the continuous process of bone remodeling that is responsible for the variation in cortical parameters with age and is the primary basis for age predicting methods. While observable changes in the occipital bone do occur with increasing age, the amount of random variation in the parameters examined preclude their use for accurate age estimation.

Adult↗
PubMed1994

Early transcription in Caenorhabditis elegans embryos.

We have analysed early transcription in devitellinized, cultured embryos of the nematode Caenorhabditis elegans by two methods: measurement of [32P]UTP uptake into TCA-precipitable material and autoradiographic detection of [3H]UTP labelling both in the presence and absence of alpha-amanitin. RNA synthesis was first detected at the 8- to 12-cell stage, and alpha-amanitin sensitivity also appeared at this time, during the cleavages establishing the major founder cell lineages. The requirements for maternally supplied versus embryonically produced gene products in early embryogenesis were examined in the same culture system by observing the effects of alpha-amanitin on cell division and the early stereotyped lineage patterns. In the presence of high levels of alpha-amanitin added at varying times from two cells onward, cell division continued until approximately the 100-cell stage and then stopped during a single round of cell division. The characteristic unequal early cleavages, orientation of cleavage planes and lineage-specific timing of early divisions were unaffected by alpha-amanitin in embryos up to 87 cells. These results indicate that embryonic transcription starts well before gastrulation in C. elegans embryos, but that although embryonic transcripts may have important early functions, maternal products can support at least the mechanics of the first 6 to 7 cell cycles.

Amanitins↗
PubMed1992

Evidence from mosaic analysis of the masculinizing gene her-1 for cell interactions in C. elegans sex determination.

Sex in Caenorhabditis elegans is determined by a regulatory cascade of seven interacting autosomal genes controlled by three X-linked genes in response to the X chromosome-to-autosome (X/A) ratio. XX animals (high X/A) develop as self-fertile hermaphrodites, and XO animals (low X/A) develop as males. The activity of the first gene in the sex-determining cascade, her-1, is required for male sexual development. XO her-1 loss-of-function mutants develop as self-fertile hermaphrodites, whereas XX her-1 gain-of-function mutants develop as masculinized intersexes. By genetic mosaic analysis using a fused free duplication linking her-1 to a cell-autonomous marker gene, we show here that her-1 expression in a sexually dimorphic cell is neither necessary nor sufficient for that cell to adopt a male fate. Our results suggest that her-1 is expressed in many, possibly all, cells and that its gene product can function non-autonomously through cell interactions to determine male sexual development.

Animals↗
PubMed1991

Evidence from reversal of handedness in C. elegans embryos for early cell interactions determining cell fates.

Many animals with overall bilateral symmetry also exhibit some left-right asymmetries with generally invariant handedness. Therefore, the left-right embryonic axis must have a consistent polarity, whose origins and subsequent effects on development are not understood. Caenorhabditis elegans exhibits such left-right asymmetries at all developmental stages. The embryonic cell lineage is asymmetric as well: although the animal is generally bilaterally symmetric, many of its contralaterally analogous cells arise from different lineages on the two sides of the embryo. I accomplished reversal of embryonic handedness by micromanipulation at the 6-cell stage, which resulted in mirror-image but otherwise normal development into healthy, fertile animals with all the usual left-right asymmetries reversed. This result demonstrates that in the 6-cell embryo the pair of anterior (AB) blastomeres on the right is equivalent to the pair on the left, and that the extensive differences in fates between lineally homologous derivatives of these cells on the two sides of the animal must be dictated by cell interactions, most of which are likely to occur early in embryogenesis.

Animals↗
PubMed1991

Handed asymmetry, handedness reversal and mechanisms of cell fate determination in nematode embryos.

Embryos of the nematode Caenorhabditis elegans exhibit left-right asymmetry with an invariant handedness. The embryonic cell lineage is asymmetrical: although the animal is generally bilaterally symmetrical with only a few left-right asymmetries, many of its contralaterally analogous cells arise via different lineages on the two sides of the embryo. Larvae and adults also exhibit left-right asymmetries with a handedness that is normally invariant. The frequency of animals with opposite handedness was increased among the progeny of adults exposed to the mutagen ethyl methanesulphonate and among animals that developed from embryos treated in early cleavage with chitinase to destroy the egg shell. Reversal of embryonic handedness was accomplished directly by micromanipulation at the 6-cell stage, resulting in mirror-image but otherwise normal development into healthy, fertile animals with all the usual left-right asymmetries reversed. This demonstrates that (1) the handedness of cell positions in the 6-cell embryo dictates handedness throughout development; (2) at this stage the pair of anterior blastomeres on the right is equivalent to the pair on the left; and (3) the extensive differences in fates of lineally homologous cells on the two sides of the animal must be dictated by cellular interactions, most of which are likely to occur early in embryogenesis and appear to have been conserved in widely diverged nematode species.

Animals↗
PubMed1991

Capric acid as a potent dilator of canine vessels in vitro and in vivo.

1. Pharmacodynamic effects of even numbered saturated fatty acids, C4-C16, were determined on isolated canine basilar and femoral arteries precontracted with PGF2 alpha. 2. The fatty acids relaxed the precontracted vessels. 3. The basilar artery was the most sensitive vessel and caprate (C10) was the most potent acid with an EC50 of 49 microM. 4. The relaxant effect was endothelium-independent. 5. Contractions elicited by norepinephrine, serotonin, and U46619 were also inhibited. 6. Caprate (C10) given intra-arterially increased femoral blood flow in a dose-dependent manner and the dose computed to increase blood flow 50% was 1.27 microM/kg.

Animals↗
PubMed1991

Sex-specific transcriptional regulation of the C. elegans sex-determining gene her-1.

Expression of the sex-determining gene her-1 is required in C. elegans for the normal male development of XO animals. Abnormal expression in XX animals, which normally develop as hermaphrodites, results in aberrant male development. We have isolated a molecular clone of the her-1 gene and have identified two transcripts that are present in XO animals at all stages of development: an abundant 0.8 kb transcript and a less abundant 1.2 kb transcript. In preparations of XX animals, the 0.8 kb transcript was observed only at very low levels in embryos or L1 larvae and the 1.2 kb transcript was not detected. Two gain-of-function her-1 mutations result in high levels of the 1.2 and 0.8 kb transcripts in XX animals. The levels of these transcripts are also elevated in XX animals carrying a loss-of-function mutation in either sdc-1 or sdc-2, consistent with the proposed roles of these genes as negative regulators of her-1. These results demonstrate that expression of the her-1 gene in males and hermaphrodites is controlled at the level of transcript synthesis or accumulation. This mode of regulation contrasts with that found for the Drosophila sex-determining genes, whose sex-specific expression is controlled by differential splicing in males and females.

Animals↗
PubMed1991

Autonomy and nonautonomy of sex determination in triploid intersex mosaics of C. elegans.

The primary sex-determining signal in Caenorhabditis elegans is the ratio of X chromosomes to sets of autosomes (X/A ratio), normally 1.0 in hermaphrodites (XX) and 0.5 in males (XO). XX triploids (X/A = 0.67) are males, but if these animals carry a partial duplication of the X chromosome such that X/A approximately equal to 0.7, they develop as intersexes that are sexually mosaic. We have analyzed these mosaics using Nomarski microscopy and in situ hybridization to obtain information on whether sex determination decisions can be made independently in different cells and tissues, and when these commitments are made. The observed patterns of male and female cells in individual animals indicate that sex determination decisions can be influenced by anterior-posterior position and that sex determination decisions can be made as late as the third larval stage of postembryonic development. Although these decisions clearly can be made independently in different lineages, they show substantial biases toward one sex or the other in individual animals. We interpret these results to suggest that sex determination in C. elegans is not entirely cell autonomous.

Animals↗
PubMed1990

The tra-1 gene determines sexual phenotype cell-autonomously in C. elegans.

The tra-1 gene plays a central role in C. elegans sex determination. XX animals develop as hermaphrodites when tra-1 is active and as males when it is not. By analyzing a large number of tra-1 genetic mosaics we have shown that, with the expected exception of vulval induction by the hermaphrodite gonad, tra-1 functions cell-autonomously, consistent with a role as an intracellular component of a signaling pathway. Moreover, all the sexual differentiation genes under tra-1 control must also function cell-autonomously. Our results have additional implications for several aspects of postembryonic development, including mechanisms of sex-specific directed cell migrations and the question of an organizer in the male tail.

Animals↗
PubMed1990

Mutations affecting embryonic cell migrations in Caenorhabditis elegans.

Four recessive mutations that affect long-range embryonic migration of the two canal-associated neurons (CANs) in C. elegans were isolated and characterized with the goal of identifying genes involved in control of directed cell movement. Mutant animals were identified initially by their "withered" tails, a phenotype associated with abnormal CAN migration; the mutants were then analyzed for abnormal cell migrations by Nomarski microscopy. Based on genetic complementation tests, the mutations were assigned to four different loci, two new (mig-10 III, mig-11 III) and two previously identified (unc-39 V, vab-8 V). Mutations at all four loci affect CAN migration with high to moderate penetrance (the percentage of mutant animals that exhibit the phenotype). In addition, two other bilaterally symmetric pairs of neurons (ALM and HSN), the mesoblast M, and a pair of coelomocyte mother cells are affected by one or more of the mutations, generally with lower penetrance. With the exceptions of HSN and the right coelomocyte mother cell, which occasionally migrate beyond their normal destinations, the cells affected appear to migrate either incompletely or not at all. All the migration phenotypes show incomplete penetrance and variable expressively, although genetic tests suggest that mutations at mig-10 and vab-8 result in complete or nearly complete loss of gene function. The variability in mutant phenotypes allowed tests for interdependence of several of the affected migrations; all those analyzed appeared independent of one another. The possible nature of the mutant defects and possible roles of these four loci in cell migration are discussed.

Animals↗
PubMed1990

Dominant maternal-effect mutations causing embryonic lethality in Caenorhabditis elegans.

We undertook screens for dominant, temperature-sensitive, maternal-effect embryonic-lethal mutations of Caenorhabditis elegans as a way to identify certain classes of genes with early embryonic functions, in particular those that are members of multigene families and those that are required in two copies for normal development. The screens have identified eight mutations, representing six loci. Mutations at three of the loci result in only maternal effects on embryonic viability. Mutations at the remaining three loci cause additional nonmaternal (zygotic) effects, including recessive lethality or sterility and dominant male mating defects. Mutations at five of the loci cause visible pregastrulation defects. Three mutations appear to be allelic with a recessive mutation of let-354. Gene dosage experiments indicate that one mutation may be a loss-of-function allele at a haploin sufficient locus. The other mutations appear to result in gain-of-function "poison" gene products. Most of these become less deleterious as the relative dosage of the corresponding wild-type allele is increased; we show that relative self-progeny viabilities for the relevant hermaphrodite genotypes are generally M/+/+ greater than M/+ greater than M/M/+ greater than M/Df greater than M/M, where M represents the dominant mutant allele.

Animals↗
PubMed1990

Mutations affecting the meiotic and mitotic divisions of the early Caenorhabditis elegans embryo.

We describe interactions between maternal-effect lethal mutations in four genes of Caenorhabditis elegans whose products appear to be involved in the meiotic and mitotic divisions of the one-cell embryo. Mitosis is disrupted by two dominant temperature-sensitive gain-of-function maternal-effect lethal mutations, mei-1(ct46) and mel-26(ct61), and by recessive loss-of-function maternal-effect lethal mutations of zyg-9. The phenotypic defects resulting from these mutations are similar. Doubly mutant combinations show a strong enhancement of the maternal-effect lethality under semipermissive conditions, suggesting that the mutant gene products interact. We isolated 15 dominant suppressors of the gain-of-function mutation mei-1(ct46). Thirteen of these suppressors are apparently intragenic, but 11 of them suppress in trans as well as cis. Two extragenic suppressors define a new gene, mei-2. The suppressor mutations in these two genes also result in recessive maternal-effect lethality, but with meiotic rather than mitotic defects. Surprisingly, most of these suppressors are also able to suppress mel-26(ct61) in addition to mei-1(ct46). The products of the four genes mei-1, mei-2, zyg-9 and mel-26 could be responsible for some of the specialized features that distinguish the meiotic from the mitotic divisions in the one-cell embryo.

Alleles↗
PubMed1990

Early C. elegans embryos are transcriptionally active.

We have developed a nucleotide incorporation assay for run-on transcription in C. elegans embryonic extracts as an approach to characterizing early transcription. The incorporation is primarily polymerase II-catalyzed RNA synthesis, producing transcripts of the expected size range for mRNAs. Incorporation is insensitive to inhibitors of reinitiation, indicating that the activity represents primarily elongation of nascent chains initiated prior to extract preparation. The transcripts produced appear to be unprocessed pre-mRNAs. Hybridization of labeled transcripts from extracts of staged embryos to a set of cloned genes suggests that the specificity of the in vitro reaction accurately reflects developmentally regulated in vivo transcription. Comparative analyses of transcription in extracts from various stages indicate that pregastrulation embryos are active transcriptionally and that the level of transcription per nucleus is approximately constant throughout embryogenesis. Furthermore, most embryonically expressed genes are already being transcribed in pregastrulation embryos. We also demonstrate that the labeled embryonic run-on transcripts can be used as probes to screen for sequences transcribed preferentially in pregastrulation embryos. There appears to be only a small set of such sequences, which could represent a previously unsuspected class of embryonically transcribed genes important for early embryogenesis.

Animals↗
PubMed1989

Genetic definition of two functional elements in a bacteriophage T4 host-range "cassette".

Gene 37 of T4 encodes the major subunit of the distal half of the tail fiber. The distal tip of the fiber, comprised of the carboxy-terminal ends of two molecules of gene 37 product (gp37), carries the principal determinant of the phage host range. The gp37 carboxyl termini recognize the bacterial surface during infection, and, in addition, include a site required for interaction with the product of gp38 during distal half-fiber assembly. In the absence of interaction with gp38, gp37 polypeptides do not dimerize. Eleven temperature-sensitive mutants with defects located near the promoter-distal end of gene 37 were tested at nonpermissive temperatures for production of an antigen that is diagnostic of distal half-fiber assembly. Six of the mutations prevent distal half-fiber assembly. The other five allow assembly of distal half fibers, which combine with proximal half fibers and attach to phage particles, but the resulting phage do not adsorb to bacteria. These two classes of mutations define two adjacent but separate genetic regions, corresponding to two different functional domains in gp37. These two regions and the neighboring gene 38 comprise a functional unit that can be considered as a host-range "cassette," with features that are strikingly similar to corresponding functional units in other unrelated as well as related phages.

Antigens, Viral↗
PubMed1988

A novel dominant transformer allele of the sex-determining gene her-1 of Caenorhabditis elegans.

We have characterized a novel dominant allele of the sex-determining gene her-1 of Caenorhabditis elegans. This allele, called n695, results in the incomplete transformation of XX animals into phenotypic males. Previously characterized recessive her-1 alleles transform XO animals into phenotypic hermaphrodites. We have identified five new recessive her-1 mutations as intragenic suppressors of n695. Three of these suppressors are weak, temperature-sensitive alleles. We show that the recessive her-1 mutations are loss-of-function alleles, and that the her-1(n695) mutation results in a gain-of-function at the her-1 locus. The existence of dominant and recessive alleles that cause opposite phenotypic transformations demonstrates that the her-1 gene acts to control sexual identity in C. elegans.

Alleles↗
PubMed1988

Mutant expression of male copulatory bursa surface markers in Caenorhabditis elegans.

In a search for molecular markers of male tail morphogenesis in C. elegans, we have detected two surface markers that are specifically observed in the copulatory bursa of adult males and the vulva of adult hermaphrodites. These markers are defined by binding of a monoclonal antibody (Ab117) and the lectin wheat germ agglutinin (WGA) to live intact animals. Expression of these markers is dependent on sex, stage and anterior-posterior position in the animal. Four of ten mutants with specific defects in bursal development show altered expression of one or both markers. Because the WGA marker can be expressed in intersexual animals with very little bursal development, posterior surface expression of this marker can serve as an indication of subtle masculinization of hermaphrodites. The timing of expression of these markers is not affected by heterochronic mutations that cause larval animals to express adult cuticles or adult animals to express larval cuticles, indicating that marker expression can be uncoupled from general cuticle development. Mutant lin-22 males, which have an anterior-to-posterior transformation of cell fates in the lateral hypodermis, ectopically express both markers in a manner consistent with a 'posteriorization' of positional information in these animals. These markers should be useful for the isolation and characterization of mutants defective in bursal and vulval development, sex determination and expression of anterior-posterior positional information.

Animals↗
PubMed1987

Isolation and characterization of a nematode transposable element from Panagrellus redivivus.

We have isolated a transposable element, designated PAT-1, from the free-living nematode Panagrellus redivivus. P. redivivus strain C15 was found to have a high spontaneous mutation frequency compared to the standard Caenorhabditis elegans laboratory strain N2. To characterize the genetic lesions occurring in spontaneous C15 mutants, we molecularly cloned the homolog of the C. elegans unc-22 gene from wild-type P. redivivus and two strains carrying spontaneous mutations in this gene. One of these mutations resulted from the insertion of a 4.8-kilobase segment of repetitive DNA. This repetitive element (PAT-1) varies in copy number (10-50 copies) and location in different P. redivivus strains and is absent from C. elegans. The element could be useful as a transformation vector for C. elegans. Our approach is a general one that could be used to isolate additional nematode transposons from other species.

Animals↗