Ralf J. Sommer (2006) WormBook "Pristionchus pacificus."

Ralf J. Sommer

[WormBook, 2006]

In the last decade, nematodes other than C. elegans have been studied intensively in evolutionary developmental biology. A few species have been developed as satellite systems for more detailed genetic and molecular studies. One such satellite species is the diplogastrid nematode Pristionchus pacificus. Here, I provide an overview about the biology, phylogeny, ecology, genetics and genomics of P. pacificus.

(2015) "Pristionchus Pacificus: A Nematode Model for Comparative and Evolutionary Biology"

[2015]

Andre Pires da Silva (2005) WormBook "Pristionchus pacificus genetic protocols."

Andre Pires da Silva

[WormBook, 2005]

Schroeder NE (2021) J Nematol "Introduction to Pristionchus pacificus anatomy."

Schroeder NE

[J Nematol, 2021]

<i>Pristionchus pacificus</i> has emerged as an important nematode species used to understand the evolution of development and behavior. While <i>P. pacificus</i> (Diplogasteridae) is only distantly related to <i>Caenorhabditis elegans</i> (Rhabditidae), both use an identical reproductive strategy, are easily reared on bacteria in Petri dishes and complete their life cycles within a few days. Over the past 25 years, several detailed light and electron microscopy studies have elucidated the anatomy of <i>P. pacificus</i> and have demonstrated clear homology to many cells in <i>C. elegans</i>. Despite this similarity, sufficient anatomical differences between <i>C. elegans</i> and <i>P. pacificus</i> have allowed the latter to be used in comparative evo-devo studies. For example, the stoma of <i>P. pacificus</i> contains a large dorsal tooth used during predation on other nematodes when supplementing its primarily bacterial diet. This review discusses the main anatomical features of <i>P. pacificus</i> with emphasis on comparison to <i>C. elegans.</i>

Eizinger A et al. (1996) European Worm Meeting "VULVA DEVELOPMENT IN PRISTIONCHUS PACIFICUS"

Lee K-Z, Eizinger A, Sommer RJ, Schlak I

[European Worm Meeting, 1996]

The vulva of Caenorhabditis elegans is formed in the central body region from three of six equivalent cells and is induced by the gonad via a signal transduction pathway. In the neodiplogasterid species Pristionchus pacificus, two of the six vulval precursor cells known from Caenorhabditis die of programmed cell death, whereas another cell is incompetent to adopt vulval cell fate. Thus, there are evolutionary changes of cell fate specification between Caenorhabditis and Pristionchus. To get more detailed insight into the molecular mechanism underlying cell fate changes during evolution, we started a genetic analysis of vulva development in Pristionchus. Pristionchus has a four day life-cycle, is easily cultured on OP50 and has six chromosomes by DAPI staining. In a small genetic pilot screen, more than 50 morphological mutants, representing the typical spectrum known from Caenorhabditis, have been isolated. In a screen of 40 000 gametes we have isolated 49 vulval defective mutants. Based on phenotype we can distinguish four groups of mutants, as well as two mutants with a unique phenotype (this includes the previously described ped-5 mutant; Sommer & Sternberg, Current Biology 6, 52-59). Group I mutants are lineage defective, group II mutants have phenotypes similar to the previously described ped-6 mutant, group III mutants are similar to the ped-4 mutant and group IV mutants are vulvaless. We are currently characterizing these mutants by lineage analysis and cell ablation experiments and perform complementation tests to reveal the number of genes isolated in the screen.

Hong RL et al. (2006) Bioessays "Pristionchus pacificus: a well-rounded nematode."

Hong RL, Sommer RJ

[Bioessays, 2006]

Nematodes pervade Earth''s biosphere and occupy innumerable ecological niches. The role of Caenorhabditis elegans as a model for developmental processes has encouraged us to cultivate a second nematode, Pristionchus pacificus, as a comparative counterpoint to address questions in development, behavior and ecology in nematode evolution. We hope that this endeavor, now more than a decade underway, will allow us to project findings onto other comparative models for biological processes. To this end, our laboratory has made an extensive genetic map and mutant screens to understand changes in developmental programs. Recently, we have been capitalizing on the whole genome sequence of P. pacificus to describe more thoroughly the molecular basis for these changes, as well as to better integrate our molecular knowledge with the biodiversity of Pristionchus species. BioEssays 28: 651-659, 2006. (c) 2006 Wiley Periodicals, Inc.

Schlak I et al. (1996) Worm Breeder's Gazette "RFLPs in Pristionchus pacificus populations."

Sommer RJ, Schlak I

[Worm Breeder's Gazette, 1996]

We have analyzed two previously isolated strains of Pristionchus pacificus for the occurrence of restriction fragment length polymorphisms. 14 of 17 randomly choosen cDNA clones give polymorphisms after hybridization to EcoRI digested genomic DNA of the populations from southern California and Washington State. This polymorphism is much higher as polymorphism found among different strains in C. elegans (Emmons et al., PNAS 76, 1333ff.). Two different scenarios could account for the observed RFLPs. First, the polymorphisms could be caused by an active transposon. Second, the two populations could be separated from one another for a long time. In order to distinguish between these two possibilities, we have started to compare most of the nucleotide sequence of the previously cloned Ppa-let-60/ras gene. Several nucleotide substitutions at third codon positions have been observed in the coding region betwen the two populations. None of these substitutions results in an aminoacid replacement. Within the intron sequences, four nucleotide substitutions as well as the deletion of three nucleotides (at two positions), have been observed. This high level of sequence diversity gives a first indication for a long evolutionary separation time of the two populations. This issue is analyzed further by sequence analysis. Nonetheless, animals of both populations can be crossed. The use of mutant animals in these crosses indicates that the F1 progeny (California/Washington) is completely fertile. These results suggest that the observed RFLPs are useful as molecular markers for chromosomal walking procedures. We have also tested, if an active transposon is present in any of the two populations. The mutant Ppa-unc-1(sy306) has a small diameter and the body muscles twitch constantly. Mutants with this phenotype have been isolated at high frequency, suggesting that the mutation causing this phenotype is a mutation in a gene homologous to the unc-22 gene of C. elegans. We have used protocols to isolate spontaneous twitcher-mutants, without being succesful to date.

Ravichandiran Kumarasamy et al. (2002) European Worm Meeting "Dna polymorphism in Pristionchus pacificus"

Ralf J Sommer, Ravichandiran Kumarasamy

[European Worm Meeting, 2002]

To understand the evolution of developmental process at the microevolutionary level, it is important to study the biogeography and the evolutionary alterations of the developmental processes in detail. To acuminate this, we are working on the satellite model Pristionchus pacificus. The genus Pristionchus has a worldwide distribution and different strains of Pristionchus pacificus exist from Washington (PS 1843), Hawaii (JU 138), Ontario (AF 8130), Poland (RS 106) and the wild type strain from California (PS 312). Previous AFLP studies showed a high degree of polymorphisms between the strains from Washington, Hawaii and California. BAC end sequencing and SSCP analysis of BAC end fragments between the strains from California and Washington confirmed these original observations. To obtain a better picture of the distribution of polymorphisms between the strains of P. pacificus, we have chosen a random 5 Kb region on Chromosome III that contains no open reading frame. Our results showed a high degree of polymorphism (3.46%) in both Washington and Hawaii when compared to the laboratory strain California. There were ~ 0.7% transitions, ~ 0.5% transversions, ~ 0.3% insertions and ~ 0.1% deletions. Most of the polymorphisms observed were single base pair events except a few which were up to 5 bp . Further studies are underway to extend this study, comparing the ceh-20 and ceh-40 genes in these strains and to eventually include the different species' of Pristionchus namely P. maupasi and P. lheritieri.

Lisa Schuster et al. (2008) European Worm Meeting "Ecological genomics of Pristionchus pacificus"

Lisa Schuster, Christoph Dieterich, Ralf J Sommer

[European Worm Meeting, 2008]

The diplogastrid nematode Pristionchus pacificus has been established. as a model system in evolutionary developmental biology and had its genome. recently being sequenced by Washington University, St. Louis. In the last. few years, detailed investigations of the ecology of Pristionchus nematodes. revealed a close association with scarab beetles in a nearly species-. specific manner. For example, P. pacificus is found on the Oriental beetle. Exomala orientalis in Japan and the East coast of the United States. P.. pacificus has a necromenic life-style: Nematodes invade the beetle as dauer. stages, wait for the insect''s death to resume development on the cadaver.. It has long been speculated that necromeny requires tolerance to host. enzyme, toxins and low oxygen concentration.. The P. pacificus genome is approx. 169 Mb in size with 142 Mb in a. robust assembly. Thus, the P. pacificus genome is substantially larger than. the one of C. elegans. We have predicted around 29.000 protein-coding genes. in the P. pacificus genome. In comparison to C. elegans, P. pacificus has. an increased number of genes involved in detoxification of xenobiotics,. such as Cytochrome P450 genes, glucosyl-transferases and ABC transporters.. Interestingly the genome of P. pacificus contains cellulase genes that were. validated experimentally and studied in more detail. Cellulase activity was. shown in the supernatant of liquid cultures of P. pacificus. Cellulases are. known as enzymes that help plant-parasitic nematodes to penetrate cellulose-. containing cell walls. This is the first time that cellulases have been. found in a nematode other than a plant parasite. Phylogenetic analysis. indicates that the seven P. pacificus cellulases are of different origin.. Therefore, we speculate that the cellulases were acquired by lateral gene. transfer which was also proposed for the cellulases of plant parasitic. nematodes. In this context, we are currently investigating cellulase. activity in other diplogastrid nematodes and could show activity in the. supernatant of members of several but not all tested genera. In addition,. we are investigating selected genes with interesting sequence profiles and. will provide an update on all of these ongoing projects.

Andreas Photos et al. (2006) Development & Evolution Meeting "Specification of the Postembryonic Mesoderm in Pristionchus pacificus"

Andreas Photos, Ralf Sommer, Arturo Gutierrez

[Development & Evolution Meeting, 2006]

Comparisons between Caenorhabditis elegans and the satellite organism Pristionchus pacificus revealed major differences in the regulation of nematode vulva development. For example, Wnt signaling is part of a negative signaling system that prevents vulva formation in P. pacificus, whereas it plays a positive role in C. elegans. We wondered if the genetic control of the second major part of the nematode egg-laying system, the sex muscles, has diverged similarly between P. pacificus and C. elegans. The sex muscles derive from the mesoblast M, which has an identical lineage in both species. Here, we describe a large-scale mutagenesis screen for postembryonic mesoderm defective mutants (pmd) that disrupt the M lineage and the sex myoblast (SM) sublineage. We isolated three complementation groups and characterized two mutations that result in a failure of proper SM fate specification and SM migration and showed that the corresponding genes encode Ppa-sem-4 and Ppa-egl-17, respectively. Ppa-sem-4 mutants have additional defects in the specification of the vulva precursor cells P(5, 7).p and experimental studies in the Ppa-egl-17 mutant background indicate a complex set of gonad-dependent and gonad-independent mechanisms required for SM migration. Mutations in Cel-sem-4 and Cel-egl-17 cause similar defects. Thus, the molecular mechanisms of SM cell specification and migration are conserved between P. pacificus and C. elegans. Currently, we are focusing on the third mutant pmd-1 with genetic and molecular techniques. pmd-1 has a novel phenotype, which has not been reported in C. elegans. After the first cell division of M, the two daughter cells exhibit an aberrant growth and division pattern causing the misspecification of the M descendants. Complementing these studies, we are performing a large scale reverse genetics approach (TMP/UV mutagenesis) to knock-out vulval and muscle patterning genes. So far, we succeeded in isolating a full Ppa-hlh-8/twist knock-out mutant causing embryonic lethality, which is in contrast to the Egl phenotype in Cel-hlh-8.