Two loci required for cytoplasmic organization in early embryos of Caenorhabditis elegans

We have identified five new alleles, including an amber allele, at each of two loci (zyg-11 II and zyg-9 II) previously identified by temperature-sensitive strict maternal-effect lethal mutations. Genetic analysis indicates that each of these genes is expressed specifically during oogenesis and encodes a protein product whose function is required only during embryogenesis. Temperature-pulse experiments suggest that the time of action of both products is during the one-cell stage of embryogenesis. Phenotypic analysis reveals that mutations in both loci lead to disorganization of the cytoplasm in early embryos and to abnormalities in at least one of the meiotic divisions. Mutations at the zyg-9 locus appear to specifically affect microtubule function in one-cell embryos while zyg-11 mutations affect many cytoplasmic properties.

Elastic fibres in the anulus fibrosus of the adult human lumbar intervertebral disc. A preliminary report

Two intervertebral discs were removed at autopsy from the lumbar region of the spine from male or female adult human cases at the following ages: 26, 34, 43, 50 and 62 years. The discs were prepared by paraffin wax embedding, sectioned serially and stained with haematoxylin and eosin or by Verhoff's elastic fibre method. Four light microscopy photomicrographs were made of randomly selected 400 micron 2 areas of anulus fibrosus matrix (two each from different levels of a single disc). Each photomicrograph was examined for elastic fibres, and the areas occupied by them were quantitated by manual planimetry. Elastic fibres were observed in all lamellae of the anulus fibrosus at lumbar levels and they were circularly, obliquely and vertically oriented. Approximately 10% of the matrix of the anulus fibrosus consisted of elastic fibres and their numbers tended to decrease slightly with increasing age of the individual.

Control of cell-cycle timing in early embryos of Caenorhabditis elegans

A technique has been developed for extruding either substantial amounts of cytoplasm without nuclei or individual nuclei with small amounts of cytoplasm from early embryos of C. elegans after perforating the eggshell with a laser microbeam. This technique, in conjunction with laser-induced cell fusion, has allowed the altering of nuclear/cytoplasmic ratios and the exposing of the nucleus of one cell to cytoplasm from another. Using these approaches the roles of nuclei and cytoplasm in determining the different cell-cycle periods of the several blastomere lineages in early embryos have been examined. It was found that nuclei in a common cytoplasm divide synchronously; enucleated blastomeres retain a cycling period characteristic of their lineage; cycling period is not substantially affected by changes in the ratio of nuclear to cytoplasmic volumes or the DNA content per cell; the period of a cell from one lineage can be substantially altered by introduction of cytoplasm from a cell of another lineage with a different period; and short-term effects of foreign cytoplasm on the timing of the subsequent mitosis differ depending on position of the donor cell in the cell cycle. These results are discussed in connection with models for the action of cytoplasmic factors in controlling cell-cycle timing.

An autosomal gene that affects X chromosome expression and sex determination in Caenorhabditis elegans

Recessive mutant alleles at the autosomal dpy-21 locus of C. elegans cause a dumpy phenotype in XX animals but not in XO animals. This dumpy phenotype is characteristic of X chromosome aneuploids with higher than normal X to autosome ratios and is proposed to result from overexpression of X-linked genes. We have isolated a new dpy-21 allele that also causes partial hermaphroditization of XO males, without causing the dumpy phenotype. All dpy-21 alleles show hermaphroditization effects in XO males that carry a duplication of part of the X chromosome and also partially suppress a transformer (tra-1) mutation that converts XX animals into males. Experiments with a set of X chromosome duplications show that the defects of dpy-21 mutants can result from interaction with several different regions of the X chromosome. We propose that dpy-21 regulates X chromosome expression and may be involved in interpreting X chromosome dose for the developmental decisions of both sex determination and dosage compensation.

Generation of asymmetry and segregation of germ-line granules in early C. elegans embryos

Germ-line granules in C. elegans embryos (P granules) can be visualized by immunofluorescence microscopy using a monoclonal antibody. In mutant zygotes with abnormal spindle orientations and in wild-type zygotes treated with the microtubule inhibitors nocodazole, colcemid, vinblastine, and griseofulvin, both P-granule segregation to the posterior pole and the concomitant pseudocleavage occur apparently normally, but the normally concurrent migration of the pronuclei is inhibited. Conversely, treatment of wild-type embryos with the microfilament inhibitors cytochalasins D and B inhibits P-granule segregation and pseudocleavage, as well as other manifestations of polarity, without preventing pronuclear migration. The results suggest that P-granule segregation does not require either the spindle or cytoplasmic microtubules, but that this process as well as generation of other asymmetries does require cytoskeletal functions that depend on microfilaments.

Attachment of tail fibers in bacteriophage T4 assembly. Identification of the baseplate protein to which tail fibers attach

A phage-neutralizing rabbit antiserum collected after immunization with tail-fiberless bacteriophage T4 particles was adsorbed with complete T4 phage. The resulting adsorbed serum inhibited tail fiber attachment in vitro. To identify the antigens against which this inhibitory activity was directed, blocking experiments were carried out with the adsorbed serum. Isolated complete baseplates and mutant-infected-cell extracts lacking known baseplate gene products but containing gene 9 product showed similar high levels of blocking activity. By contrast, both tail-fiberless particles lacking gene 9 product and infected-cell extracts made with gene 9 mutants showed 30-fold to 100-fold lower blocking activity. These results strongly support the conclusion that gene 9 product is the baseplate protein to which tail fibers attach.

Location of specific messenger RNAs in Caenorhabditis elegans by cytological hybridization

We have developed an autoradiographic technique for detecting specific Caenorhabditis elegans messenger RNA molecules in situ by hybridization of labeled, cloned DNA probes to fixed tissue sections and squashes of embryos and adults. We report analyses with probes of actin and collagen gene sequences from a C. elegans genomic clone library. Hybridization is RNase sensitive and tissue specific. In adults the actin probe, which recognizes cytoplasmic as well as muscle actin mRNA, hybridizes strongly to muscle and distal gonad (ovary), somewhat less strongly to maturing oocytes, and weakly to intestine. The collagen probe hybridizes weakly to distal gonad and intestine and very strongly to subcuticular tissues, in particular to the hypodermal cells and syncytial cytoplasm of the lateral hypodermal ridges, which are the sites of cuticle synthesis. In embryos, hybridization to squashes indicates that actin message is present at fertilization, decreases during early cleavage, and then increases again during morphogenesis. By contrast, collagen message is absent until the 100-cell stage and then increases rapidly during morphogenesis. The number of cells labeled is consistent with the view that the collagen probe hybridizes to hypodermal precursor cells. We estimate that our present methods can detect messages representing about 0.2% or more of the total mRNA population, and increases in this sensitivity should be possible. Therefore, the cytological hybridization technique should be useful for determining temporal and spatial patterns of specific mRNA distributions during development, at least for abundant and moderately abundant messages.

Genetic analysis of life-span in Caenorhabditis elegans

Crosses between Bristol and Bergerac strains of the self-fertilizing hermaphroditic nematode Caenorhabditis elegans do not show the heterosis effects for life-span that complicate analysis of interstrain crosses with Drosophila or mice. Instead they yield F1 progeny with life-spans similar to those of the parent strains. By analysis of life-span variation among progeny F2 populations from such crosses and by two independent analyses of life-spans among recombinant inbred lines derived from F2 individuals by 18 rounds of self-fertilization, we estimate that the heritability of life-span in C. elegans is between 20% and 50%. Recombinant inbred lines show a range in mean life-spans of 10 days to 31 days compared to life-spans of about 18 days for each of the two parental strains. We conclude that life-span variation in C. elegans has a substantial genetic component and that this organism offers promising opportunities for selective breeding of longer-lived strains and genetic analysis of senescence.

Developmental Determinants in Embryos of Caenorhabditis elegans

C. elegans is proving useful for the study of cell determination in early embryos. Breeding experiments with embryonic lethal mutants show that abnormal embryogenesis often results from defective gene function in the maternal parent, suggesting that much of the information for normal embryonic development is laid down during oogenesis. Analysis of a gut-specific differentiation marker in cleavage-arrested embryos has provided evidence that the potential for this differentiation behaves as a cell-autonomous internally segregating developmental determinant, which is present from the 2-cell stage onward and is partitioned into the gut precursor cell during early cleavage divisions. Visible prelocalized cytoplasmic granules that segregate with a particular cell lineage have heen observed in the embryonic germline precursor cells by fluorescent antibody staining. Whether these granules play a role in germline determina... [remainder of abstract missing in original].

Immunofluorescence visualization of germ-line-specific cytoplasmic granules in embryos, larvae, and adults of Caenorhabditis elegans

By using fluorescent antibody staining, we have followed cytoplasmic granules unique to germ-line cells throughout the life cycle of Caenorhabditis elegans. These elements, designated P granules, are segregated exclusively to germ-line precursor cells during early embryogenesis. Prior to mitosis at each of the early cleavages that produce a somatic and germ-line daughter cell, the granules become localized in the region of cytoplasm destined for the germ-line daughter. After the 16-cell stage, the granules appear to be associated with the nuclear envelope. P granules persist in the germ cells throughout the larval and adult stages. The P granules are similar in number, size, and distribution to germ-line-specific structures identified as "germinal plasm" by electron microscopy in C. elegans embryos.

Assembly of bacteriophage T4 tail fibers: identification and characterization of the nonstructural protein gp57

Formation of both the tail fiber and the baseplate of bacteriophage T4 depends on the product of T4 gene 57. A single amber mutation in that gene causes loss of two T4-specific proteins. Their molecular weights are 18,000 and about 6,000, respectively, based on their electrophoretic mobilities in SDS-polyacrylamide gels. E. coli carrying a cloned T4 DNA fragment of about 700 basepairs, which directs the synthesis of the smaller protein only, specifically supports the growth of gene 57 amber mutants. We conclude that the small protein is a functional product of gene 57.

Tooth size and morphology in a recent Australian aboriginal population from Broadbeach, South East Queensland

Odontometric and morphologic observations were made of the dentition of skeletal remains of australian aborigines from Broadbeach, S.E. Queensland. Tooth size, especially of the molars, was found to be significantly larger than that reported for other recent Aboriginal populations. Tooth morphology also differed, with a higher frequency of five cusped second molars, and a lower frequency of shoveling and Carabelli's cusp than previously reported as typical of Australian aborigines.

Bacteriophage T4 morphogenesis as a model for assembly of subcellular structure

The sequence of steps in bacteriophage T4 assembly has been elucidated by using a combination of genetic, biochemical, and ultrastructural techniques. The phage head, tail, and tail fibers are assembled via independent pathways, and then are jointed to form the complete virus. Current knowledge of these three pathways is reviewed briefly. Two general insights emerging from phage assembly studies are (1) a realization of the importance of kinetic controls, and (2) recognition of the role of nonstructural accessory proteins in assembly. Controls of protein association rates by a proposed heterocooperation mechanism can account for the strict sequential ordering of steps in complex self-assembly pathways such as that of T4 tail assembly. The same mechanism can explain how proteins capable of polymorphic assembly are induced to form correct structures rather than aberrant ones of similar stability. Nonstructural accessory proteins provide additional means for enhancing rates of interactions of specific structural proteins by mechanisms that may be analogous to those of enzyme catalysis. The insights gained from bacteriophage assembly probably apply to organellogenesis in general.

Role of the host cell in bacteriophage T4 development. II. Characterization of host mutants that have pleiotropic effects on T4 growth

Mutant host-defective Escherichi coli that fail to propagate bacteriophage T4 and have a pleiotropic effect on T4 development have been isolated and characterized. In phage-infected mutant cells, specific early phage proteins are absent or reduced in amount, phage DNA synthesis is depressed by about 50%, specific structural phage proteins, including some tail and collar components, are deficient or missing, and host-cell lysis is delayed and slow. Almost all phage that can overcome the host block carry mutantions that map in functionally undefined 'nonessential' regions of the T4 genome, most near gene 39. The mutant host strains are temperature sensitive for growth and show simultaneous reversion of the ts phenotype and the inability to propagate T4+. The host mutations are cotransduced with ilv (83 min) and may lie in the gene for transcription termination factor rho.

Segregation of developmental potential in early embryos of Caenorhabditis elegans

We have followed the appearance of differentiation markers in cleavage-inhibited and uninhibited early blastomeres of C. elegans and have compared the cleavage patterns of blastomeres in partial and complete embryos. The results indicate that at least some primary differentiation of embryonic cells is determined by internal factors that segregate in early cleavages, whereas patterns of cleavage are dictated by both internally segregating determinants and external cues.

Role of the host cell in bacteriophage T4 development. I. Characterization of host mutants that block T4 head assembly

To study the role of the host cell in bacteriophage T4 infection, we selected more than 600 mutant host-defective bacteria that absorbed and were killed by phage T4+ but were unable to support its growth. The mutants were grouped into seven classes by the growth patterns of T4 phages carrying compensating mutations (go mutants [grows on]), selected on four prototype host-defective strains. Lysis and DNA synthesis experiments indicated that classes A, AD, D, and B (the majority of the host-defective mutants) block T4+ development at an assembly step, class C mutants affect an early stage in phage development, and class F mutants appear to act at more than one stage. Analysis of T4+ infection in the assembly-defective mutants by in vitro complementation, electron microscopy, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the host-defective mutations interfere with T4+ capsid formation at the level of phage gene 31 function, before assembly of any recognizable capsid structure. The mutations map near purA, but at two or possibly three different sites. The go mutant phages able to overcome the host defect carry mutations in either gene 31, as found by others for similar defective hosts, or in the gene for the major capsid protein (gene 23). The gene 23 go mutations do not bypass the requirement for gene 31 function. These results suggest that at least three components must interact to initiate T4 head assembly: gp31, gp23, and one or more host factors. The compensatory effects of mutational alterations in these components are highly allele specific, consistent with the view that phage and host components interact directly in protein complexes.

Bacteriophage T4 RNA ligase is gene 63 product, the protein that promotes tail fiber attachment to the baseplate

RNA ligase and tail fiber attachment activities, normally induced following bacteriophage T4 infection of Escherichia coli, are not induced when gene 63 amber mutants of T4 infect nonpermissive host cells. Both activities are induced when these mutants infect permissive hosts, or when revertants of these mutants infect nonpermissive hosts. When one of these mutants infects a host that carries supF, both activities are more than normally heat labile. RNA ligase, purified to homogeneity, promotes the tail fiber attachment reaction in vitro with a specific activity similar to that of the most highly purified preparations of gene 63 product isolated on the basis of tail fiber attachment activity. We conclude that T4 RNA ligase is gene 63 product. The RNA ligase and tail fiber attachment reactions differ in requirements and in response to some inhibitors, suggesting that the two activities of the gene 63 product may be mechanistically unrelated.