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Abstract
Caenorhabditis elegans adult animals exhibit an inherent chirality of fiber orientation in the basal layer of the cuticle, as well as a naturally invariant but experimentally reversible handedness in the left-right (L-R) asymmetry of the body plan. We have examined the relationship between cuticle chirality and body handedness in normal and L-R reversed animals, using Roller (Rol) mutants and transmission electron microscopy to monitor cuticle properties. Rol phenotypes, several of which have been shown to result from mutations in cuticle collagen genes, are characterized by an invariant, allele-specific handedness in their direction of rolling. We show for several alleles that this direction is not affected by L-R reversal of the body plan. We further show, by electron microscopy, that the chiral orientation of cuticle fibers in animals with normal cuticle is not reversed by L-R body-plan reversal. We conclude that cuticle chirality must be established independently of body-plan handedness. The cues that establish cuticle chirality are still unknown, as are the causes for different rolling directions in different Roller mutants. We discuss the question of how cuticle chirality maintains its independence, and how the orientations of the fiber layers may be determined.
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Van Auken K, Weaver DC, Edgar LG, Wood WB. Caenorhabditis elegans embryonic axial patterning requires two recently discovered posterior-group Hox genes. Proc Natl Acad Sci U S A 2000; 97:4499-503. [PMID: 10781051 PMCID: PMC18263 DOI: 10.1073/pnas.97.9.4499] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Hox genes encode highly conserved transcription factors that control regional identities of cells and tissues along the developing anterior-posterior axis, probably in all bilaterian metazoans. However, in invertebrate embryos other than Drosophila, Hox gene functions remain largely unknown except by inference from sequence similarities and expression patterns. Recent genomic sequencing has shown that Caenorhabditis elegans has three Hox genes of the posterior paralog group [Ruvkun, G. & Hobert, O. (1998) Science 282, 2033-2041]. However, only one has been previously identified genetically, and it is not required for embryonic development [Chisholm, A. (1991) Development (Cambridge, U.K.) 111, 921-932]. Herein, we report identification of the remaining two posterior paralogs as the nob-1 gene and the neighboring php-3 gene. Elimination of nob-1 and php-3 functions causes gross embryonic defects in both posterior patterning and morphogenetic movements of the posterior hypodermis, as well as posterior-to-anterior cell fate transformations and lethality. The only other Hox gene essential for embryogenesis is the labial/Hox1 homolog ceh-13, required for more anterior patterning [Brunschwig, K., Wittmann, C., Schnabel, R., Burglin, T. R., Tobler, H. & Muller, F. (1999) Development (Cambridge, U.K.) 126, 1537-1546]. Therefore, essential embryonic patterning in C. elegans requires only Hox genes of the anterior and posterior paralog groups, raising interesting questions about evolution of the medial-group genes.
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Li W, Boswell R, Wood WB. mag-1, a homolog of Drosophila mago nashi, regulates hermaphrodite germ-line sex determination in Caenorhabditis elegans. Dev Biol 2000; 218:172-82. [PMID: 10656761 DOI: 10.1006/dbio.1999.9593] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Caenorhabditis elegans gene mag-1 can substitute functionally for its homolog mago nashi in Drosophila and is predicted to encode a protein that exhibits 80% identity and 88% similarity to Mago nashi (P. A. Newmark et al., 1997, Development 120, 3197-3207). We have used RNA-mediated interference (RNAi) to analyze the phenotypic consequences of impairing mag-1 function in C. elegans. We show here that mag-1(RNAi) causes masculinization of the germ line (Mog phenotype) in RNA-injected hermaphrodites, suggesting that mag-1 is involved in hermaphrodite germ-line sex determination. Epistasis analysis shows that ectopic sperm production caused by mag-1(RNAi) is prevented by loss-of-function (lf) mutations in fog-2, gld-1, fem-1, fem-2, fem-3, and fog-1, all of which cause germ-line feminization in XX hermaphrodites, but not by a her-1(lf) mutation which causes germ-line feminization only in XO males. These results suggest that mag-1 interacts with the fog, fem, and gld genes and acts independently of her-1. We propose that mag-1 normally allows oogenesis by inhibiting function of one or more of these masculinizing genes, which act during the fourth larval stage to promote transient sperm production in the hermaphrodite germ line. When the Mog phenotype is suppressed by a fog-2(lf) mutation, mag-1(RNAi) also causes lethality in the progeny embryos of RNA-injected, mated hermaphrodites, suggesting an essential role for mag-1 during embryogenesis. The defective embryos arrest during morphogenesis with an apparent elongation defect. The distribution pattern of a JAM-1::GFP reporter, which is localized to boundaries of hypodermal cells, shows that hypodermis is disorganized in these embryos. The temporal expression pattern of the mag-1 gene prior to and during morphogenesis appears to be consistent with an essential role of mag-1 in embryonic hypodermal organization and elongation.
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Streit A, Li W, Robertson B, Schein J, Kamal IH, Marra M, Wood WB. Homologs of the Caenorhabditis elegans masculinizing gene her-1 in C. briggsae and the filarial parasite Brugia malayi. Genetics 1999; 152:1573-84. [PMID: 10430584 PMCID: PMC1460716 DOI: 10.1093/genetics/152.4.1573] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The masculinizing gene her-1 in Caenorhabditis elegans (Ce-her-1) encodes a novel protein, HER-1A, which is required for male development. To identify conserved elements in her-1 we have cloned and characterized two homologous nematode genes: one by synteny from the closely related free-living species C. briggsae (Cb-her-1) and the other, starting with a fortuitously identified expressed sequence tag, from the distantly related parasite Brugia malayi (Bm-her-1). The overall sequence identities of the predicted gene products with Ce-HER-1A are only 57% for Cb-HER-1, which is considerably lower than has been found for most homologous briggsae genes, and 35% for Bm-HER-1. However, conserved residues are found throughout both proteins, and like Ce-HER-1A, both have putative N-terminal signal sequences. Ce-her-1 produces a larger masculinizing transcript (her-1a) and a smaller transcript of unknown function (her-1b); both are present essentially only in males. By contrast, Cb-her-1 appears to produce only one transcript, corresponding to her-1a; it is enriched in males but present also in hermaphrodites. Injection of dsRNA transcribed from Cb-her-1 into C. briggsae hermaphrodites (RNA interference) caused XO animals to develop into partially fertile hermaphrodites. Introducing a Cb-her-1 construct as a transgene under control of the C. elegans unc-54 myosin heavy chain promoter caused strong masculinization of both C. briggsae and C. elegans hermaphrodites. Introduction of a similar Bm-her-1 construct into C. elegans caused only very weak, if any, masculinization. We conclude that in spite of considerable divergence the Cb gene is likely to be a functional ortholog of Ce-her-1, while the function of the distantly related Bm gene remains uncertain.
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Li W, Streit A, Robertson B, Wood WB. Evidence for multiple promoter elements orchestrating male-specific regulation of the her-1 gene in Caenorhabditis elegans. Genetics 1999; 152:237-48. [PMID: 10224257 PMCID: PMC1460597 DOI: 10.1093/genetics/152.1.237] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The sex-determining gene her-1 is required for male development in Caenorhabditis elegans. In XO males, two her-1 mRNAs, her-1a and her-1b, are transcribed from two separate promoters: P1, located in the 5'-flanking region, and P2, located in the large second intron. In XX hermaphrodites, accumulation of both her-1 transcripts is repressed by the sdc genes, which in turn are negatively regulated by the xol-1 gene. When introduced into a xol-1(y9) background, transgenic arrays, including 3.4 kb of her-1 intron 2 sequence (P2), result in phenotypes that mimic those of sdc(lf) mutants, including suppression of XO lethality and masculinization of both XX and XO animals. The masculinization, but not the suppression of XO lethality, is dependent on endogenous her-1 activity. These effects could therefore result from sequestration (titration) of sdc gene products by sequences in the arrays, causing derepression of her-1 (masculinizing effect) and disruption of the dosage compensation machinery (allowing survival of XO animals). We used these effects as an assay in a deletion analysis of the two her-1 promoter regions to define potential cis-regulatory sites required for the putative titration. Several regions in P2 contributed to these effects. P1 was effective only in combination with certain P2 sequences and only if a particular P1 site previously implicated in her-1 repression was intact. These results suggest that normal repression of transcription from P1 in XX animals may involve cooperative interaction with sequences in the P2 region. In experiments to test for a possible role of the her-1b transcript in regulation of sdc genes, no significant effects could be demonstrated.
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Suzuki Y, Yandell MD, Roy PJ, Krishna S, Savage-Dunn C, Ross RM, Padgett RW, Wood WB. A BMP homolog acts as a dose-dependent regulator of body size and male tail patterning in Caenorhabditis elegans. Development 1999; 126:241-50. [PMID: 9847238 DOI: 10.1242/dev.126.2.241] [Citation(s) in RCA: 174] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
We cloned the dbl-1 gene, a C. elegans homolog of Drosophila decapentaplegic and vertebrate BMP genes. Loss-of-function mutations in dbl-1 cause markedly reduced body size and defective male copulatory structures. Conversely, dbl-1 overexpression causes markedly increased body size and partly complementary male tail phenotypes, indicating that DBL-1 acts as a dose-dependent regulator of these processes. Evidence from genetic interactions indicates that these effects are mediated by a Smad signaling pathway, for which DBL-1 is a previously unidentified ligand. Our study of the dbl-1 expression pattern suggests a role for neuronal cells in global size regulation as well as male tail patterning.
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Fay DS, Stanley HM, Han M, Wood WB. A Caenorhabditis elegans homologue of hunchback is required for late stages of development but not early embryonic patterning. Dev Biol 1999; 205:240-53. [PMID: 9917360 DOI: 10.1006/dbio.1998.9096] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have cloned a Caenorhabditis elegans homologue of the Drosophila gap gene hunchback (hb) and have designated it hbl-1 (hunchback-like). hbl-1 encodes a predicted 982-amino-acid protein, containing two putative zinc-finger domains similar to those of Drosophila Hunchback. The gene is transcribed embryonically, but unlike the maternally expressed Drosophila hb, its mRNA is not detected in C. elegans oocytes. A hbl-1::gfp reporter is expressed primarily in ectodermal cells during embryonic and larval development. Double-stranded RNA-interference (RNAi) was used to indicate hbl-1 loss-of-function phenotypes. Progeny of hbl-1(RNAi) hermaphrodites exhibit a range of defects; the most severely affected progeny arrest as partially elongated embryos or as hatching, misshapen L1 larvae. Animals that survive to adulthood exhibit variably dumpy (Dpy), uncoordinated (Unc), and egg-laying defective (Egl) phenotypes, as well as defects in vulval morphology (Pvl). Abnormal organization of hypodermal cells and expression of a hypodermal marker in hbl-1(RNAi) animals suggests that most of the phenotypes observed could be due to improper specification of hypodermal cells. The pattern of hbl-1 expression is similar to that reported for the leech hunchback homologue Lzf-2, suggesting that these proteins may have similar biological functions in diverse species with cellular embryos.
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Elvery MW, Savage NW, Wood WB. Radiographic study of the broadbeach aboriginal dentition. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 1998; 107:211-9. [PMID: 9786335 DOI: 10.1002/(sici)1096-8644(199810)107:2<211::aid-ajpa7>3.0.co;2-x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
This study forms part of a larger anthropological investigation of the Ngaraangbal Aboriginal Tribe's ancestral burial ground at Broadbeach, Australia. It examines the dentition, records the associated pathology in a noninvasive manner, and relates this to the likely subsistence diet of the tribe. The Broadbeach osteological collection was returned for reburial in 1985; however, radiographic and photographic records of 36 adult males were available. These form the basis of our study. The pathology noted in the study sample was compared with a representative sample (n = 38) of pre-European Aboriginal remains from throughout Queensland for verification purposes only. Rates of dental pathology and injury were calculated from the radiographic and photographic records. There was a significant rate of tooth-wear related intra-bony pathology (4.0%), moderate to severe alveolar bone loss, and heavy dental attrition, of which the mandibular posterior teeth were the most severely affected. Caries prevalence (0.8%) was low for hunter-gatherer populations. A large number of molar pulp chambers had a distinctive "cruciate" morphology resulting from the formation of secondary dentine and pulp stones. Injuries and abnormalities included upper central incisor avulsion (58.3%) and taurodontism. These results support the proposal that the Ngaraangbal tribe was a hunter-gatherer population subsisting on an abrasive diet that included marine foods.
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Kawasaki I, Shim YH, Kirchner J, Kaminker J, Wood WB, Strome S. PGL-1, a predicted RNA-binding component of germ granules, is essential for fertility in C. elegans. Cell 1998; 94:635-45. [PMID: 9741628 DOI: 10.1016/s0092-8674(00)81605-0] [Citation(s) in RCA: 291] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Germ cells are distinct from somatic cells in their immortality, totipotency, and ability to undergo meiosis. Candidates for components that guide the unique germline program are the distinctive granules observed in germ cells of many species. We show that a component of germ granules is essential for fertility in C. elegans and that its primary function is in germline proliferation. This role has been revealed by molecular and genetic analyses of pgl-1. PGL-1 is a predicted RNA-binding protein that is present on germ granules at all stages of development. Elimination of PGL-1 results in defective germ granules and sterility. Interestingly, PGL-1 function is required for fertility only at elevated temperatures, suggesting that germline development is inherently sensitive to temperature.
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Knight JK, Wood WB. Gastrulation initiation in Caenorhabditis elegans requires the function of gad-1, which encodes a protein with WD repeats. Dev Biol 1998; 198:253-65. [PMID: 9659931] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Gastrulation in Caenorhabditis elegans is normally initiated by inward migration of the two gut precursor (E) cells at the 26-cell stage. A strong loss-of-function, temperature-sensitive, embryonic lethal mutation in the maternally required gene gad-1 (gastrulation defective) prevents gastrulation initiation. In embryos from homozygous mutant gad-1 (ct226) hermaphrodites reared at 25 degrees C, the E cells divide early with abnormal spindle orientations and fail to migrate into the embryo, and no subsequent gastrulation movements occur. These embryos continue to develop and differentiate the major cell types, but they undergo little morphogenesis. The temperature-sensitive period of the mutant is during early embryogenesis, prior to gastrulation onset. The predicted translation product of the cloned gad-1 gene includes six beta-transducin-related repeats of the WD motif, which has been implicated in protein-protein interactions. The ct226 mutation alters a conserved residue in one of these repeats. Injection of gad-1 antisense RNA into wild-type hermaphrodites mimics the mutant phenotype in progeny embryos. We conclude that the gad-1 gene product is required for initiation of gastrulation in C. elegans.
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Powell-Coffman JA, Bradfield CA, Wood WB. Caenorhabditis elegans orthologs of the aryl hydrocarbon receptor and its heterodimerization partner the aryl hydrocarbon receptor nuclear translocator. Proc Natl Acad Sci U S A 1998; 95:2844-9. [PMID: 9501178 PMCID: PMC19657 DOI: 10.1073/pnas.95.6.2844] [Citation(s) in RCA: 145] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/23/1997] [Indexed: 02/06/2023] Open
Abstract
The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor, until now described only in vertebrates, that mediates many of the carcinogenic and teratogenic effects of certain environmental pollutants. Here, we describe orthologs of AHR and its dimerization partner AHR nuclear translocator (ARNT) in the nematode Caenorhabditis elegans, encoded by the genes ahr-1 and aha-1, respectively. The corresponding proteins, AHR-1 and AHA-1, share biochemical properties with their mammalian cognates. Specifically, AHR-1 forms a tight association with HSP90, and AHR-1 and AHA-1 interact to bind DNA fragments containing the mammalian xenobiotic response element with sequence specificity. Yeast expression studies indicate that C. elegans AHR-1, like vertebrate AHR, requires some form of post-translational activation. Moreover, this requirement depends on the presence of the domains predicted to mediate binding of HSP90 and ligand. Preliminary experiments suggest that if AHR-1 is ligand-activated, its spectrum of ligands is different from that of the mammalian receptor: C. elegans AHR-1 is not photoaffinity labeled by a dioxin analog, and it is not activated by beta-naphthoflavone in the yeast system. The discovery of these genes in a simple, genetically tractable invertebrate should allow elucidation of AHR-1 function and identification of its endogenous regulators.
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Abstract
Like most animals, C. elegans and other nematodes exhibit several internal left-right asymmetries with an essentially invariant (dextral) handedness. Handedness is established in early cleavage, resulting in a markedly left-right-asymmetric embryo on which bilateral symmetry must be superimposed later in embryogenesis. Some of the asymmetric cell interactions that accomplish this have been identified, but the mechanism that initially establishes dextral rather than sinistral handedness is not understood, in C. elegans or any other embryo. Analysis of mutations that result in reversal of handedness, such as spn-1 in C. elegans, should help elucidate this process. A model involving centriolar segregation is proposed as a possible mechanism for handedness choice.
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Abstract
Most animal species exhibit left-right asymmetry in their body plans and show a strong bias for one handedness over the other. The mechanism of handedness choice, recognized as an intriguing problem over a century ago, is still a mystery. However, from recent advances in understanding when and how asymmetry arises in both invertebrates and vertebrates, developmental pathways for establishment and maintenance of left-right differences are beginning to take shape, and speculations can be made on the initial choice mechanism.
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Abstract
Dosage compensation in Caenorhabditis elegans involves the sex-specific recruitment to the X chromosome of a protein complex, the nature of which suggests that there are mechanistic links between chromosome segregation and global transcriptional regulation.
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Pettitt J, Wood WB, Plasterk RH. cdh-3, a gene encoding a member of the cadherin superfamily, functions in epithelial cell morphogenesis in Caenorhabditis elegans. Development 1996; 122:4149-57. [PMID: 9012534 DOI: 10.1242/dev.122.12.4149] [Citation(s) in RCA: 77] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Several genes that encode members of the cadherin superfamily have been identified in Caenorhabditis elegans. Based on the roles of cadherins in vertebrates and Drosophila, it is expected that they function in the control of epithelial morphogenesis, an event which is poorly understood at the molecular level in C. elegans. Reporter genes under the control of upstream sequences from one of these genes, cdh-3, are expressed in developing epithelial cells, but also in a number of neuroectodermal cells that extend processes along some of these epithelial cells. We generated a loss-of-function mutation in cdh-3 by transposon-mediated deletion mutagenesis. This mutation affects the morphogenesis of a single cell, hyp10, which forms the tip of the nematode tail. The lack of detectable defects associated with the other cells expressing cdh-3 reporter constructs hints at the existence of other genes that can compensate for cdh-3 loss of function.
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Powell-Coffman JA, Knight J, Wood WB. Onset of C. elegans gastrulation is blocked by inhibition of embryonic transcription with an RNA polymerase antisense RNA. Dev Biol 1996; 178:472-83. [PMID: 8812143 DOI: 10.1006/dbio.1996.0232] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Cleavage and gastrulation initiation in Caenorhabditis elegans embryos are characterized by an invariant temporal and spatial pattern of cell divisions and cell movements. Although bulk embryonic transcription does not begin until gastrulation onset, some transcription can be detected as early as the 4-cell stage. To determine whether any early transcripts are required for normal cleavage-stage patterning, we blocked transcription in embryos by injecting hermaphrodite parental gonads with RNA antisense to the ama-1 gene, which encodes the large subunit of RNA polymerase II. This treatment prevented the expression of a reporter gene driven by an early embryonic promoter but did not detectably perturb the maternally controlled segregation of the germ line P granules or the pattern of cell division through the first four cleavages. In the fifth cell cycle, however, the two endodermal precursor (E) cells divided early and abnormally and failed to initiate gastrulation. The embryos arrested between the sixth and seventh cell cycles with less than 100 cells. These results indicate that embryonically transcribed gene products are required for gastrulation initiation. They also demonstrate the efficacy of a method for blocking embryonic transcription that may be useful in other organisms.
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Seydoux G, Mello CC, Pettitt J, Wood WB, Priess JR, Fire A. Repression of gene expression in the embryonic germ lineage of C. elegans. Nature 1996; 382:713-6. [PMID: 8751441 DOI: 10.1038/382713a0] [Citation(s) in RCA: 256] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The distinction between soma and germline was recognized more than a century ago: somatic cells form the body of an organism, whereas germ cells serve to produce future generations. In Caenorhabditis elegans, the separation of some and germline occurs through a series of asymmetrical divisions, in which embryonic germline blastomeres divide unequally to produce one somatic daughter and one germline daughter. Here we show that after each asymmetrical division, embryonically transcribed RNAs are detected in somatic, but not germline, blastomeres. This asymmetry depends on the activity of the germline specific factor, PIE-1. In the absence of PIE-1, embryonically transcribed RNAs are detected in both somatic and germline blastomeres. Furthermore, ectopic expression of PIE-1 in somatic blastomeres can significantly reduce the accumulation of new transcripts in these cells. Taken together, these results suggest that germ-cell fate depends on an inhibitory mechanism that blocks new gene expression in the early embryonic germ lineage.
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Wood WB, Bergmann D, Florance A. Maternal effect of low temperature on handedness determination in C. elegans embryos. DEVELOPMENTAL GENETICS 1996; 19:222-30. [PMID: 8952064 DOI: 10.1002/(sici)1520-6408(1996)19:3<222::aid-dvg5>3.0.co;2-b] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
C. elegans embryos, larvae, and adults exhibit several left-right asymmetries with an invariant dextral handedness, which first becomes evident in the embryo at the 6-cell stage. Reversed (sinistral) handedness was not observed among > 10,000 N2 adults reared at 16 degrees C or 20 degrees C under standard conditions. However, among the progeny of adults reproducing at 10 degrees C, the frequency of animals with sinistral handedness was increased to approximately 0.5%. Cold pulse experiments indicated that the critical period for this increase was in early oogenesis, several hours before the first appearance of left-right asymmetry in the embryo. Hermaphrodites reared at 10 degrees C and mated with males reared at 20 degrees C produced sinistral outcross as well as sinistral self-progeny, indicating that the low temperature effect on oocytes was sufficient to cause reversals. Increased frequency of reversal was also observed among animals developed from embryos lacking the egg shell. Possible mechanisms for the control of embryonic handedness are discussed in the context of these results, including the hypothesis that handedness could be dictated by the chirality of a gametic component.
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Cool SM, Hendrikz JK, Wood WB. Microscopic age changes in the human occipital bone. J Forensic Sci 1995; 40:789-96. [PMID: 7595323] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
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.
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Perry MD, Trent C, Robertson B, Chamblin C, Wood WB. Sequenced alleles of the Caenorhabditis elegans sex-determining gene her-1 include a novel class of conditional promoter mutations. Genetics 1994; 138:317-27. [PMID: 7828816 PMCID: PMC1206151 DOI: 10.1093/genetics/138.2.317] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
In the control of Caenorhabditis elegans sex determination, the her-1 gene must normally be activated to allow male development of XO animals and deactivated to allow hermaphrodite development of XX animals. The gene is regulated at the transcriptional level and has two nested male-specific transcripts. The larger of these encodes a small, novel, cysteine-rich protein responsible for masculinizing activity. Of the 32 extant mutant alleles, 30 cause partial or complete loss of masculinizing function (lf), while 2 are gain-of-function (gf) alleles resulting in abnormal masculinization of XX animals. We have identified the DNA sequence changes in each of these 32 alleles. Most affect the protein coding functions of the gene, but six are in the promoter region, including the two gf mutations. These two mutations may define a binding site for negative regulators of her-1. Three of the four remaining promoter mutations are single base changes that cause, surprisingly, temperature-sensitive loss of her-1 function. Such conditional promoter mutations have previously not been found among either prokaryotic or eukaryotic mutants analyzed at the molecular level.
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Storfer-Glazer FA, Wood WB. Effects of chromosomal deficiencies on early cleavage patterning and terminal phenotype in Caenorhabditis elegans embryos. Genetics 1994; 137:499-508. [PMID: 8070660 PMCID: PMC1205972 DOI: 10.1093/genetics/137.2.499] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
We have analyzed pregastrulation cleavage patterns in Caenorhabditis elegans embryos homozygous for various chromosomal deficiencies. By two different estimates these deficiencies represent between 37 and 49% of the genome, including the entire X chromosome and substantial portions of each of the five autosomes. Among these genomic regions, we find none whose absence causes defects in pregastrulation cleavage patterns. We can conclude that there are at most very few genes whose transcription after fertilization is required for normal early patterning of cell divisions. We also scored terminal phenotypes of the homozygous deficiency embryos for stage of arrest and for expression of three tissue-specific differentiation markers. Based on these phenotypes, we have identified regions of the genome that are required for completion of cell proliferation, expression of gut differentiation and entry into morphogenesis. Somewhat surprisingly, embryos in which cell proliferation is arrested at less than 20% of the normal cell number can nevertheless initiate morphogenesis and undergo elongation to the twofold stage. Our results are consistent with the view that many early events in C. elegans embryogenesis are controlled exclusively by maternally produced gene products. However, they are also consistent with the likely possibility that, at least in some deficiency embryos, although cleavage patterns may be normal, blastomere identities are not. In this respect the early cleavages may differ from later lineages, in which cell division patterns appear to be characteristic of cell identity.
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Yandell MD, Edgar LG, Wood WB. Trimethylpsoralen induces small deletion mutations in Caenorhabditis elegans. Proc Natl Acad Sci U S A 1994; 91:1381-5. [PMID: 7906415 PMCID: PMC43162 DOI: 10.1073/pnas.91.4.1381] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
To examine the mutagenic spectrum of 4,5',8-trimethylpsoralen (TMP) in Caenorhabditis elegans, we isolated mutations in the unc-22 and pal-1 genes following TMP mutagenesis and analyzed them for restriction fragment length polymorphisms by Southern blot. Eleven of 21 unc-22 mutations exhibited restriction fragment length polymorphisms, 8 of which were deletions of between 0.10 and 15 kb in length. Both of two pal-1 mutations were also small deletions within this size range. Comparison of our results with previous studies on mutagenesis by gamma-rays and x-rays suggests that the mutagenic spectrum of TMP may be similar. TMP should be useful in generating mutations that cause complete loss of function of single genes and that are likely to result in allele-specific DNA polymorphisms.
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Abstract
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.
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Abstract
Two genes that control dauer formation in the soil nematode Caenorhabditis elegans have direct effects on senescence.
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