Free-living Nematode Panagrellus Research Articles

The development of nematode behaviour: stage-specific behaviour in Panagrellus redivivus

Larvae of the free-living nematode Panagrellus redivivus differ from adults in their attraction to bacteria. Under osmotic stress larvae coil, while adults do not. Larvae do not travel as far, but undergo more looping, turning, and reversal activity than do normal adults. A behavioural mutant, corkscrew, with primary expression in adults, shows differences in behaviour at each stage of the life cycle.

Relative ribosomal RNA cistron multiplicity in oocytes and postembryonic stages of the eutelic nematode Panagrellus silusiae.

The number of ribosomal RNA cistrons has been measured in the total DNA extracted from L2 juvenile and adult stages of the free-living nematode Panagrellus silusiae. Saturation hybridization studies with homologous rRNA indicate that both stages have about 275 ribosomal genes per haploid equivalent. Using homologous 125I-labelled rRNA for in situ hybridization, the mean number of silver grains per DNA content for oocyte, hypodermis and gut nuclei was similar. The mean DNA contents of maturing oocyte, hypodermis and gut nuclei are about 20C, 2C, and 10C respectively. We conclude that rDNA amplication alone is insufficient to account for the variation in DNA content of oocytes and that postembryonic development in this eutelic organism occurs without a significant differential increase in the number of ribosomal cistrons per worm.

Programmed synthesis of collagen during postembryonic development of the nematode Panagrellus silusiae

The relative rate of collagen synthesis in the free-living nematode Panagrellus silusiae during postembryonic development was found to be discontinuous by measuring either the incorporation of tritium into material extracted as collagen or the amount of collagen-bound tritiated proline and hydroxyproline after 2-hr incubations of whole worms with [ 3H]proline. A peak of collagen production preceded each of the three molts that were examined. Moreover, protocollagen prolyl hydroxylase activity during each intermolt period paralleled the pattern of collagen synthesis. On the other hand, a triphasic pattern was not observed when noncollagenous proteins were labeled with either [ 3H]tryptophan or [ 3H]leucine. In addition, the level of soluble radioactive proline that accumulates in whole organisms after 2-hr incubation periods did not fluctuate appreciably during postembryonic development. The mean ratio of hydroxy-proline to proline in a number of collagen samples extracted at various times during the maturation phase was 0.113 ± 0.040. Pulse and chase experiments with [ 3H]proline indicated that most of the collagen synthesized during a peak period is lost after the second ecdysis following the labeling interval. In contrast, a considerable proportion of the collagen synthesized during nonpeak periods is retained throughout the postembryonic period. It is postulated that the modulated pattern of collagen biosynthesis in Panagrellus reflects, for the most part, a quantitative regulation of the production of cuticular collagen during postembryonic development.

Properties and synthesis of ribosomal RNA in the free-living nematode Panagrellus silusiae

The nominal S values of ribosomes and ribosomal subunits extracted from the free-living nematode Panagrellus silusiae are similar to those of other eukaryotic organisms. Upon heating (70°C, 15 min) a 5.5-S RNA is released from the larger ribosomal RNA (27 S; 1.40 · 10 6 daltons). Unlike other protostomes, however, the 27-S rRNA does not dissociate in an orderly manner to yield 18-S components. The electrophoretic mobility of the small ribosomal RNA species (18 S; 0.72 · 10 6 daltons) is unaltered by heat treatment. The base composition of both Panagrellus rRNA species has a 51% G+C content. Labelling worms with either [ Me- 3H]methionine or [ 14C]uridine at various stages of postembryonic development and subsequent analysis of the extracted RNA revealed eight radioactive fractions, two of which were the mature ribosomal RNAs. From both the time sequence of appearance of the eight RNA species and the relative degree of methylation of the various RNA fractions two maturation pathways for ribosomal RNA processing were deduced. A 37-S (3.6 · 10 6 daltons) RNA is the precursor to both 27-S and 18-S RNA. During processing about two-fifths of the original transcriptional unit is lost. In this organism the “transcribed spacer” regions may be methylated although alternate interpretations have not been precluded.

Sex-specific aging in the nematode Panagrellus redivivus

Females of the free-living nematode Panagrellus redivivus have a greater mean life span than do males. Unmated animals live longer than mated individuals. Decreased nutritional levels or increased temperature decrease life span. The sex differences in life expectancy are also shown by behavioral activity and osmotic fragility. Behavioral activity decreases in older animals.

DNA accumulation during oogenesis in the free-living nematode Panagrellus silusiae

DNA contents of nuclei at different stages of gonadogenesis, gametogenesis and embryogenesis in the free-living nematode Panagrellus silusiae were measured by Feulgen microspectrophotometry. Somatic nuclei of gonadal tissue in both males and females have DNA values that range from 2C to 4C. Relative DNA values identified meiotic processes during spermatogenesis. In the adult female, developing oocytes amass an amount of nuclear DNA in excess of the expected 4C equivalent. The chromatin of these nuclei is diffuse with varyingsized clumps of Feulgen-positive material. Throughout oogenesis maturing oocytes remain uninucleolate. — The extra oocyte DNA is distributed proportionately at each of the first four cleavage divisions; thereafter, its presence is not resolvable. — A standardized microphotometric comparison indicated that the amount of DNA in the unit genome of P. silusiae is about 0.1 pg. The oviduct oocytes accumulate about 3.6 pg DNA in excess of a 4C equivalent. The kind of DNA that builds up during oogenesis in this organism is not known.

Studies on the mechanisms of accumulation of phorate by the free-living nematode Panagrellus redivivus

Accumulation and metabolism of the organophosphate pesticide, phorate by the free-living nematode Panagrellus redivivus was studied under anaerobic conditions and in the presence of carbon monoxide or SKF 525A, and compared with results obtained under normal, aerobic conditions and using heat-killed nematodes. Both phorate hydrolysis and side-chain oxidation were inhibited under anaerobic conditions and with heat-killed nematodes, but only hydrolysis was affected in the presence of carbon monoxide. The much greater phorate accumulation in the nematodes under anaerobic conditions and with carbon monoxide could be explained by this metabolic inhibition. SKF 525A had no significant effect on phorate metabolism or accumulation. The possible mechanisms involved in phorate breakdown by P. redivivus are discussed.

Uptake and metabolism of phorate by the free-living nematode Panagrellus redivivus

The free-living nematode Panagrellus redivivus was incubated with the organophosphorus pesticide, phorate, and the rates of uptake and metabolism determined by radiochemical methods. Extensive catalysis of phorate hydrolysis and side-chain oxidation was observed, and the location of this activity within the system is discussed. Little accumulation of phorate or its metabolites was found in the nematodes.

Sterol biosynthesis in the free-living nematode Panagrellus redivivus.

The fate of the known sterol precursor squalene 2,3-oxide was investigated in the free-living nematode Panagrellus redivivus. The nematodes were cultured axenically in the presence of [4-(3)H]squalene 2,3-oxide. Radioactivity was found in the total lipids of the isolated nematodes. Essentially all of the radioactivity encountered in the total lipids was found in the non-saponifiable fraction. The components present in the non-saponifiable fraction were separated and isolated by t.l.c. Three labelled components were identified by a combination of t.l.c., g.l.c. and mass spectroscopy. It is established that P. redivivus has the capacity for biosynthesis of lanosterol. No labelled C(27) sterols could be detected.

Isolation and identification of lanosterol as a normal constituent of the lipids of the free living nematode Panagrellus redivivus

1.1. The lipids of the free-living nematode Panagrellus redivivus were examined for C30 triterpenes.2.2. The common sterol precursor lanosterol was identified as a constituent of the lipids of Panagrellus redivivus.

Nematode Morphogenesis: Localization of Controlling Regions by Laser Microbeam Surgery

Laser microbeam studies reveal that postembryonic development of the free-living nematode Panagrellus silusiae is under the control of specific regions. Growth is regulated by the hindgut, and ecdysis by nerve cell bodies situated anterior to the nerve ring, and gonad development is under the control of the nerve ring. This latter event is presumably neuronally mediated, while the other events are under hormonal control.

Effects of growth inhibitors on development of the reproductive system of the free-living nematode Panagrellus redivivus (Cephalobidae)

The effects of inhibitors of ribonucleic acid (RNA), protein, and deoxyribonucleic acid (DNA) synthesis on growth and gonad development during synchronized post embryonic development of the free-living nematode Panagrellus redivivus was examined. Actinomycin D (AMD) and actidione blocked growth and gonad development at each stage but to different degrees, while hydroxyurea had slight inhibitory effects on growth but stopped gonad differentiation. Fourth-stage larvae placed in AMD or actidione failed to undergo gonad differentiation. Hydroxyurea blocked the morphological organization of the gonad but had little if any effect on growth; a high level of cell proliferation is evident while gonad differentiation is never achieved. Renewal of DNA synthesis in the fourth molt is required to complete development. The uncoupling of growth and gonad development as a result of inhibition with AMD and actidione suggests that macromolecular information for division and proliferation of the gonad is laid down quite early, while the informational synthesis for differentiation occurs quite late.

Regulation of nematode behavior by physical means

Application of microwave radiation, laser microbeam irradiation, and short pulses of electric current stimulates changes in normal swimming behavior of the free-living nematode Panagrellus silusiae. The altered behavior, termed activated behavior, involves increased movement of the ends of the nematode, rapid changes in orientation, and an increase in the proportion of the swimming time that the nematode is curved such that the ends are pointing in the same direction. Laser microbeam studies indicate that the receptor for mating attraction is situated on the spicule. Panagrellvs silusiae shows mating attraction with two strains of P. redivivus, but the P. redivivus strains only attract P. silusiae or the other P. redivivus strain. Experiments with pulses of electric current indicate that the nematodes can be conditioned and that this conditioning requires RNA and protein synthesis.

Effects of cyclohexamide and hydroxyurea on mating behavior and its development in the free-living nematode Panagrellus silusiae (de Man 1913) Goodey, 1945

Females of the free-living dioecious nematode Panagrellus silusiae that have undergone postembryonic development in hydroxyurea do not attract males, and treated males do not respond to normal females. Nematodes placed in hydroxyurea as adults have normal gonads and retain the sexual attraction system. Hydroxyurea has no effect upon copulatory behavior of adult animals. Treatment of adult females with actidione stops production of attractant, although production resumes within 24 h after removal of the females from actidione. Actidione treatment of males has no effect upon the response to attractant by males or on copulation. It is proposed that sexual attraction depends on complete development of the reproductive system, but that copulation does not.

Cytoplasmic organelles present during spermatogenesis in the free-living nematode Panagrellus silusiae

By electron microscopy it was found that two kinds of cytoplasmic organelles occur during spermatogenesis in the free-living nematode Panagrellus silusiae. One type of organelle is called a vesicular body (v-body) and lines the complete internal cell surface of the spherical and aflagellate sperm. V-bodies (about 0.35 μm × 0.6 μm) are formed in the primary spermatocytes and after meiosis they migrate to the surface of the spermatid. In the primary spermatocytes, before the appearance of v-bodies, many double membrane - bound, ovoid crystalline bodies (c-bodies) are formed. These bodies (about 0.5 μm × 0.7 μm) subsequently degenerate and no trace of their fibrillar material is observed in the spermatozoon.The mature sperm is devoid of microtubules, centrioles, Golgi material, and acrosomal-like structures; however, numerous mitochondria lie beneath the surface vesicles and in the central region of the mature sperm the chromatin occurs as discrete condensed clumps.

Number and DNA content of nuclei in the free-living nematode Panagrellus silusiae at each stage during postembryonic development.

Nuclei from the four major tissues of the nematode Panagrellus silusiae were enumerated and examined using Feulgen microspectrophotometry at each stage during postembryonic development. The number of nuclei in the hypodermis, nerve, and intestine remains fairly constant during maturation, but there is a slight increase (∼57%) in the number of muscle nuclei. Thus, this organism is not stringently eutelic. The total number of somatic nuclei is about 600. DNA values of hypodermis and nerve nuclei were unimodal and adult nuclei had 2C amounts of DNA. The DNA distribution of muscle nuclei reflects the pattern expected for a tissue in which a portion of the nuclei are undergoing DNA synthesis. Intestinal nuclei accumulated DNA in the absence of nuclear division and in the adult the nuclei fall into discrete DNA classes which correspond to a geometric series of the 2C value. It is concluded that chromatin diminution does not occur in this species. In addition, the relationship in the different tissues of nuclear DNA content to nuclear volume and cell size is discussed.

Selection for adaptation to increased temperatures in free-living nematodes—II. Some lipid differences in Panagrellus redivivus

1. 1. One strain of the free-living nematode Panagrellus redivivus was selected for adaptation to 32°C; another from the same basal population was kept at 20°C. 2. 2. When tested under both temperatures the 32°C strain contained approximately twice the amount of total lipid (25 per cent) and approximately twice the amount of the fatty acid 18:2 in the neutral lipid fraction (14 per cent) than did the 20°C strain identically tested. 3. 3. The odd chain fatty acid 17:0 was identified in both strains.

Nematode morphogenesis: fine structure of the molting cycles in Panagrellus silusiae (de Man 1913) Goodey 1945

The mode of formation of a new cuticle in the free-living nematode Panagrellus silusiae is similar at each of the three postpartum molts. Molting begins with the appearance of filaments adjacent to the hypodermis. The new cuticle accumulates material and lacks organization during the early stage of the molt. The edge of the new cuticle adjacent to the old cuticle is composed of an amorphous row of particles and a filamentous region abuts the hypodermis. Eventually, a complete cuticle is produced beneath the preexisting one.The shedding of the old cuticle varies in different molts. In the larval molts (L2 to L3 and L3 to L4) and the molt to the adult female the cuticle is discarded piecemeal. During the molt to the adult male the old cuticle splits and is shed as a single piece.Before completion of ecdysis in the final female molt, the new cuticle folds extensively. This folding does not occur during any other molt.Resorption of the old cuticle is never observed. There is no microscopic evidence of protein synthesis in the interchordal hypodermis during the molting process.

Nematode morphogenesis: fine structure of the cuticle of each stage of the nematode, Panagrellus silusiae (de Man 1913) Goodey 1945.

The fine structure of the cuticle of each of the five stages of the free-living nematode Panagrellus silusiae (de Man 1913) Goodey 1945 has been examined. The cuticle plan is made up of a few regions: (1) an outer region (~350 Å) which consists of three layers: a thin outer layer, an electron transparent layer, and a thin but diffuse inner layer; (2) an inner region which has virtually no resolvable substructure other than a striated layer. This layer is not usually seen in the early stages of development but is readily apparent in the L4 and adult stages. The pattern of the cuticle is the same for each stage.The lateral fields—alae—reveal a definite differentiation during the life cycle; in the larval stages they are mere bulges but in the adults they take on a distinct four-lobed shape. The cuticle lining the pharynx consists of two regions, and there is never a striated band present nor does the cuticle increase in width during nematode growth.The interchordal hypodermis is devoid of endoplasmic reticulum, Golgi material, and mitochondria, but in some regions glycogen is found.