Cleavage plane specification in C. elegans: how to divide the spoils.
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Animals↗
Biomedical subjects
S Strome
Publications and source records attributed to S Strome.
Macrorestriction analysis of Caenorhabditis elegans genomic DNA.
The usefulness of genomic physical maps is greatly enhanced by linkage of the physical map with the genetic map. We describe a "macrorestriction mapping" procedure for Caenorhabditis elegans that we have applied to this endeavor. High molecular weight, genomic DNA is digested with infrequently cutting restriction enzymes and size-fractionated by pulsed field gel electrophoresis. Southern blots of the gels are probed with clones from the C. elegans physical map. This procedure allows the construction of restriction maps covering several hundred kilobases and the detection of polymorphic restriction fragments using probes that map several hundred kilobases away. We describe several applications of this technique. (1) We determined that the amount of DNA in a previously uncloned region is < 220 kb. (2) We mapped the mes-1 gene to a cosmid, by detecting polymorphic restriction fragments associated with a deletion allele of the gene. The 25-kb deletion was initially detected using as a probe sequences located approximately 400 kb away from the gene. (3) We mapped the molecular endpoint of the deficiency hDf6, and determined that three spontaneously derived duplications in the unc-38-dpy-5 region have very complex molecular structures, containing internal rearrangements and deletions.
Animals↗
A sperm-supplied factor required for embryogenesis in C. elegans.
The paternal-effect embryonic-lethal gene, spe-11, is required for normal development of early C. elegans embryos. Spe-11 embryos fail to complete meiosis, form a weak eggshell, fail to orient properly the first mitotic spindle, and fail to undergo cytokinesis. Here we report cloning and sequencing of the spe-11 gene, which encodes a novel protein. As predicted by the paternal-effect mutant phenotype, the gene is expressed during spermatogenesis but is not detectable in females undergoing oogenesis, and the protein is present in mature sperm. To investigate whether SPE-11's essential function is during spermatogenesis or whether sperm-delivered SPE-11 functions in the newly fertilized embryo, we engineered animals to supply SPE-11 to the embryo through the oocyte rather than through the sperm. We found that maternal expression is sufficient for embryonic viability. This result demonstrates that SPE-11 is not required during spermatogenesis, and suggests that SPE-11 is a sperm-supplied factor that participates directly in development of the early embryo. In contrast to the many known maternal factors required for embryogenesis, SPE-11 is the first paternally contributed factor to be genetically identified and molecularly characterized.
Amino Acid Sequence↗
Segregation of germ granules in living Caenorhabditis elegans embryos: cell-type-specific mechanisms for cytoplasmic localisation.
Germ granules are ribonucleoprotein particles that are thought to function in germline specification in invertebrates and possibly in vertebrates. In Caenorhabditis elegans, these structures, termed P granules, are partitioned to the germline P cells during the early embryonic divisions. By injecting a fluorescently labelled anti-P-granule antibody into the C. elegans germline syncitium, we followed P-granule segregation in live embryos using laser-scanning confocal microscopy. We show that, in early P cells (P0 and P1), P-granule partitioning is achieved primarily by their migration through the cytoplasm towards the site of formation of the germline daughter cell. A different mechanism appears to operate in later P cells (P2 and P3): P granules associate with the nucleus and move with it toward the site of formation of the germline daughter cell, where they are then deposited. At each division, there is also disassembly or degradation of those P granules that remain in the cytoplasm destined for the somatic daughter cell. Microfilaments, microtubules and the product of the gene mes-1 are required for the normal pattern of P-granule segregation in P2.
Actin Cytoskeleton↗
Phenotypic and molecular analysis of mes-3, a maternal-effect gene required for proliferation and viability of the germ line in C. elegans.
mes-3 is one of four maternal-effect sterile genes that encode maternal components required for normal postembryonic development of the germ line in Caenorhabditis elegans. mes-3 mutant mothers produce sterile progeny, which contain few germ cells and no gametes. This terminal phenotype reflects two problems: reduced proliferation of the germ line and germ cell death. Both the appearance of the dying germ cells and the results of genetic tests indicate that germ cells in mes-3 animals undergo a necrotic-like death, not programmed cell death. The few germ cells that appear healthy in mes-3 worms do not differentiate into gametes, even after elimination of the signaling pathway that normally maintains the undifferentiated population of germ cells. Thus, mes-3 encodes a maternally supplied product that is required both for proliferation of the germ line and for maintenance of viable germ cells that are competent to differentiate into gametes. Cloning and molecular characterization of mes-3 revealed that it is the upstream gene in an operon. The genes in the operon display parallel expression patterns; transcripts are present throughout development and are not restricted to germ-line tissue. Both mes-3 and the downstream gene in the operon encode novel proteins.
Amino Acid Sequence↗
Transformation of the germ line into muscle in mes-1 mutant embryos of C. elegans.
Mutations in the maternal-effect sterile gene mes-1 cause the offspring of homozygous mutant mothers to develop into sterile adults. Lineage analysis revealed that mutant offspring are sterile because they fail to form primordial germ cells during embryogenesis. In wild-type embryos, the primordial germ cell P4 is generated via a series of four unequal stem-cell divisions of the zygote. mes-1 embryos display a premature and progressive loss of polarity in these divisions: P0 and P1 undergo apparently normal unequal divisions and cytoplasmic partitioning, but P2 (in some embryos) and P3 (in most embryos) display defects in cleavage asymmetry and fail to partition lineage-specific components to only one daughter cell. As an apparent consequence of these defects, P4 is transformed into a muscle precursor, like its somatic sister cell D, and generates up to 20 body muscle cells instead of germ cells. Our results show that the wild-type mes-1 gene participates in promoting unequal germ-line divisions and asymmetric partitioning events and thus the determination of cell fate in early C. elegans embryos.
Animals↗
Specification and development of the germline in Caenorhabditis elegans.
Maternal-effect sterile (mes) genes encode maternal components that are required for establishment and development of the germline. Five such genes have been identified in the nematode Caenorhabditis elegans. Mutations in one of the genes result in defects in the asymmetric division and cytoplasmic partitioning that generate the primordial germ cell P4 at the 16-24-cell stage of embryogenesis. As a result of these defects, the P4 cell is transformed into a muscle progenitor and mutant embryos develop into sterile adults with extra body muscles. Mutations in the other four mes genes do not affect formation of the germline during embryogenesis, but result in drastically reduced proliferation of the germline during post-embryonic stages and in an absence of gametes in adults. The failure to form gametes may reflect a defect in germline specification or may be a consequence of reduced germline proliferation. We are currently testing these two possibilities. In addition to the mes gene products, wild-type function of the zygotic gene glp-4 is required for normal post-embryonic proliferation of the germline. Germ cells in glp-4 mutant worms are arrested in prophase of the mitotic cell cycle and are unable to enter meiosis and form gametes. Thus, following establishment of the germ lineage in the early embryo, both maternal and zygotic gene products work in concert to promote the extensive proliferation of the germline and to enable germ cells to generate functional gametes.
Animals↗
Laryngeal transplantation: a program for investigating new parameters.
Laryngeal transplantation was actively investigated in the late 1960s and early 1970s using a dog model. An expanded knowledge base in immunobiology, pharmacology, and deglutition makes reassessment timely after an approximately 20-year hiatus. The basic parameters to be evaluated include varied methods of preservation, optimal immunosuppressive drug regimens, and the role of radiation therapy. Our current research protocol addressing the latter considerations is outlined, including a brief introduction of a new animal model developed specifically for this purpose. We will ultimately attempt to answer the question: Is laryngeal transplantation feasible?
Anastomosis, Surgical↗
A comparison of preservation techniques in a vascularized rat laryngeal transplant model.
In earlier laryngeal transplantation studies by Takenouchi, et al., the longest ischemic interval tolerated was 45 minutes. A new animal model and enhanced preservative solutions made reassessment timely. This study evaluated two determinants of graft viability: 1. the duration of ischemia and 2. the composition of the preservative media. Three groups of viable transplants were assessed. Groups I and II were preserved with iced heparinized saline with respective ischemic intervals of 3 and 6 hours. Group III was preserved with the Wisconsin solution during a 20-hour ischemic interval. All animals were sacrificed at 24 hours. Representative sections of group I confirmed viability whereas group II exhibited both clinical and histologic evidence of irreversible vascular change. In contrast, most representative sections in group III had little demonstrable change. These data suggest that laryngeal allografts can endure prolonged ischemic intervals if properly maintained.
Adenosine↗
Determination of cleavage planes.
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Animals↗
The effects of cyclosporin A on transplanted rat allografts.
Since 1983, Cyclosporin A (CsA) has been the most successful primary drug in preventing rejection of organ transplants. This study was designed to determine the efficacy and dose response of CsA in preventing rejection of LBNF-1 rat allografts to Lewis recipients. Four groups of animals were studied. Group I served as the control, and groups II, III, and IV were given daily intramuscular doses of CsA for 1 month. The groups were given doses of 5 mg/kg, 7.5 mg/kg, and 10 mg/kg, respectively. Sixty-eight animals were transplanted to get eight viable transplanted animals at 1 month in each CsA group. Laryngeal viability was assessed with both clinical and histological parameters. Groups II, III, and IV had representative clinically viable larynges. The histology varied and had some correlation with CsA dosage. Group II evidenced changes ranging from mild to severe rejection. Group III was more homogeneous with the most severe change being characterized as mild-to-moderate rejection. Group IV was the most uniform with all representative specimens showing only limited infiltration of inflammatory cells with intact mucosa and submucosal glands (mild rejection). None of the CsA groups evidenced the squamous metaplasia characteristic of the control group. CsA can prevent rejection of laryngeal allografts from LBNF-1 donors to Lewis recipients.
Anastomosis, Surgical↗
Developmental biology. The germ of the issue.
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Abdomen↗
Histopathologic correlates of acute laryngeal allograft rejection in a rat model.
This study used both clinical and histopathologic criteria to define the sequence and time parameters of rejection in histoincompatible vascularized rat laryngeal allografts. Clinical onset of rejection was characterized at 1 week by graft edema. Pathologic examination at this time revealed arterial wall thickening and a diffuse lymphocytic and macrophage mucosal infiltrate. At 14 days, the graft was encased in an inflammatory exudate with no visible cartilaginous structure. This correlated microscopically with a lymphocytic infiltrate of the lamina propria, loss of minor salivary glands, and squamous metaplasia of the surface respiratory epithelium. Arterial thrombosis was always correlated with tissue necrosis, but venous occlusion, occurring more than 2 days after transplantation, was not an independent determinant of graft viability. Definition of the time sequence and histopathology of rejection will allow future determination of the efficacy of various immunosuppressive regimens.
Acute Disease↗
Rat model for a vascularized laryngeal allograft.
A new rat model was developed to reexamine the potential for laryngeal transplantation. The final anatomic derivation evolved from two earlier developmental phases. The first model had only a single arterial anastomosis; the second had an end-to-end arterial anastomosis with an end-to-end arteriovenous shunt. The final product employed an end-to-side arterial shunt and an end-to-side arteriovenous shunt for revascularization. The allografts were sited in tandem with the intact recipient larynges and were not innervated. A total of 16 animals were studied in phase 3; 2 died and the remaining 14 had a 64% arterial patency at intervals of 1 to 14 days. Our purpose is to detail the relevant technical considerations of this new model and compare it with historical controls.
Anastomosis, Surgical↗
Characterization of a germ-line proliferation mutation in C. elegans.
The C. elegans germ line is generated by extensive proliferation of the two germ-line progenitor cells present in newly hatched larvae. We describe genetic and phenotypic characterization of glp-4, a locus whose product is required for normal proliferation of the germ line. glp-4(bn2ts) mutant worms raised at the restrictive temperature contain approximately 12 germ nuclei, in contrast to the 700-1000 present in wild-type adults. The few germ cells present in sterile glp-4 adults appear to be arrested at prophase of the mitotic cell cycle. This cell-cycle disruption prevents the germ cells from entering meiosis and differentiating into gametes. Shifting sterile glp-4 worms to the permissive temperature enables their germ cells to undergo extensive proliferation and form gametes, demonstrating that the bn2-induced cell-cycle arrest is reversible and that proliferation and differentiation of germ cells can be uncoupled from development of the somatic gonad. The glp-4(bn2ts) mutation can be used to generate large populations of worms that are severely depleted in germ cells, facilitating determination of whether any gene of interest is expressed in the germ line or soma or both.
Animals↗
Identification of grandchildless loci whose products are required for normal germ-line development in the nematode Caenorhabditis elegans.
To identify genes that encode maternal components required for development of the germ line in the nematode Caenorhabditis elegans, we have screened for mutations that confer a maternal-effect sterile or "grandchildless" phenotype: homozygous mutant hermaphrodites produced by heterozygous mothers are themselves fertile, but produce sterile progeny. Our screens have identified six loci, defined by 21 mutations. This paper presents genetic and phenotypic characterization of four of the loci. The majority of mutations, those in mes-2, mes-3 and mes-4, affect postembryonic germ-line development; the progeny of mutant mothers undergo apparently normal embryogenesis but develop into agametic adults with 10-1000-fold reductions in number of germ cells. In contrast, mutations in mes-1 cause defects in cytoplasmic partitioning during embryogenesis, and the resulting larvae lack germ-line progenitor cells. Mutations in all of the mes loci primarily affect the germ line, and none disrupt the structural integrity of germ granules. This is in contrast to grandchildless mutations in Drosophila melanogaster, all of which disrupt germ granules and affect abdominal as well as germ-line development.
Animals↗
Laryngeal transplantation. The future.
The ethics, justification, history, future, and rejection of laryngeal transplantation are examined in this article. The authors believe that laryngeal transplantation will be a viable alternative for a select group of patients before the end of this century.
Animals↗
Brief cytochalasin-induced disruption of microfilaments during a critical interval in 1-cell C. elegans embryos alters the partitioning of developmental instructions to the 2-cell embryo.
We are investigating the involvement of the microfilament cytoskeleton in the development of early Caenorhabditis elegans embryos. We previously reported that several cytoplasmic movements in the zygote require that the microfilament cytoskeleton remain intact during a narrow time interval approximately three-quarters of the way through the first cell cycle. In this study, we analyze the developmental consequences of brief, cytochalasin D-induced microfilament disruption during the 1-cell stage. Our results indicate that during the first cell cycle microfilaments are important only during the critical time interval for the 2-cell embryo to undergo the correct pattern of subsequent divisions and to initiate the differentiation of at least 4 tissue types. Disruption of microfilaments during the critical interval results in aberrant division and P-granule segregation patterns, generating some embryos that we classify as 'reverse polarity', 'anterior duplication', and 'posterior duplication' embryos. These altered patterns suggest that microfilament disruption during the critical interval leads to the incorrect distribution of developmental instructions responsible for early pattern formation. The strict correlation between unequal division, unequal germ-granule partitioning, and the generation of daughter cells with different cell cycle periods observed in these embryos suggests that the three processes are coupled. We hypothesize that (1) an 'asymmetry determinant', normally located at the posterior end of the zygote, governs asymmetric cell division, germ-granule segregation, and the segregation of cell cycle timing elements during the first cell cycle, and (2) the integrity or placement of this asymmetry determinant is sensitive to microfilament disruption during the critical time interval.
Actin Cytoskeleton↗