Patterning in the C. elegans embryo

Recent studies reveal preliminary insights into the mechanisms of embryonic patterning in Caenorhabditis elegans. It appears that both embryonic axes and early blastomere fates are determined by a combination of segregating determinants and cell interactions, under the control of maternally expressed genes. Later in embryogenesis, some regional identities are specified by a group of homeotic selector genes homologous to the HOM-C clusters in other animals. Intervening stages of specification, which could link these two classes of genes in a regulatory hierarchy, are beginning to be investigated.

Function of the her-1 gene is required for maintenance of male differentiation in adult tissues of C. elegans

Function of the sex-determining gene her-1 is required in XO embryos of C. elegans to specify male development. Using a temperature-sensitive mutant of her-1, we show that when XO males reared at a permissive temperature are shifted as adults to a nonpermissive temperature, they initiate vitellogenin synthesis in the intestine and oocyte production in the germline. A similar shift has no effect on her-1(+) males. We conclude that sexual differentiation of the intestine and germline is plastic, requiring her-1 expression throughout adulthood for maintenance of the male state.

Molecular characterization of the her-1 gene suggests a direct role in cell signaling during Caenorhabditis elegans sex determination

We have characterized two transcripts from the male-determining her-1 locus in Caenorhabditis elegans. The larger transcript, which appears more important for male development, is predicted to encode a novel 175-amino-acid, cysteine-rich polypeptide with an apparent amino-terminal signal sequence and potential cleavage and glycosylation sites. Expression of a full-length cDNA construct for the larger transcript driven by a body-wall-myosin promoter causes extensive masculinization of all sexually dimorphic tissues in XX (normally hermaphrodite) animals. This activity is dependent on the presence of the her-1 signal sequence or a substitute synthetic signal sequence in the encoded polypeptide. These results suggest that a secreted product of the her-1 gene dictates male development.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Molecular analysis of X chromosome dosage compensation in Caenorhabditis elegans

We used a convenient quantitative dot blot assay to measure transcript levels for two X chromosome-linked genes, myo-2 and act-4, in the nematode Caenorhabditis elegans. We show that there is dosage compensation of transcript levels for these two genes between XX hermaphrodites and X0 males and that a mutation in the dpy-21 gene, postulated from genetic analysis to be involved in control of X chromosome expression, can affect these transcript levels in the manner predicted. However, we observe the dpy-21 effects only at some stages of the life cycle and not at others. These results are generally consistent with earlier genetic and molecular evidence.

Genetic analysis of X-chromosome dosage compensation in Caenorhabditis elegans

We have shown that the phenotypes resulting from hypomorphic mutations (causing reduction but not complete loss of function) in two X-linked genes can be used as a genetic assay for X-chromosome dosage compensation in Caenorhabditis elegans between males (XO) and hermaphrodites (XX). In addition we show that recessive mutations in two autosomal genes, dpy-21 V and dpy-26 IV, suppress the phenotypes resulting from the X-linked hypomorphic mutations, but not the phenotypes resulting from comparable autosomal hypomorphic mutations. This result strongly suggests that the dpy-21 and dpy-26 mutations cause increased X expression, implying that the normal function of these genes may be to lower the expression of X-linked genes. Recessive mutations in two other dpy genes, dpy-22 X and dpy-23 X, increase the severity of phenotypes resulting from some X-linked hypomorphic mutations, although dpy-23 may affect the phenotypes resulting from the autosomal hypomorphs as well. The mutations in all four of the dpy genes show their effects in both XO and XX animals, although to different degrees. Mutations in 18 other dpy genes do not show these effects.

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.

Prevention of arteriolar rarefaction in the spontaneously hypertensive rat by exposure to simulated high altitude

Microvascular alterations associated with reversal of hypertension by exposure to simulated high altitude were investigated in the gracilis muscle of the spontaneously hypertensive rat (SHR). Male, 4-week-old SHR were either placed in a hypobaric chamber (SHR-HA) at 430 mmHg or maintained at ambient barometric pressure (SHR-SL) for 8-10 or 12-14 weeks. Measurements of microvascular diameter and density were made by closed-circuit television microscopy. Mean arterial blood pressure was significantly lower in the SHR-HA groups. Functional arteriolar rarefaction occurred in SHR-SL at 8-10 weeks while structural arteriolar rarefaction occurred after 12-14 weeks. In contrast, neither functional nor structural rarefaction of arterioles was observed in the SHR-HA groups. Although functional rarefaction of capillaries did occur in SHR-HA, it was less than that in SHR-SL. Total capillary density, however, was similar in SHR-SL and SHR-HA after 12-14 weeks. Vasoconstriction was decreased in SHR-HA and vasodilated arteriolar diameters were greater than those of SHR-SL. These results show that simulated high altitude lowered blood pressure in SHR and resulted in a microcirculatory bed resembling that seen in a normotensive animal.

Urbanization within the Indonesian economy: a policy dilemma

"Most Third World countries have serious problems relating to rapid urban growth but attempts to solve urban problems have generally failed. This paper looks at the urban issues of one country, Indonesia, and the attempts by the Indonesian government to control rural to urban migration. Contradictions between macroeconomic and urban policies, however, have undermined government programmes."