Sommer RJ (1995) International C. elegans Meeting "CHANGES OF APOPTOSIS AND CELL COMPETENCE ALTER THE SIZE OF THE VULVA EQUIVALENCE GROUP IN NEMATODE EVOLUTION: A GENETIC ANALYSIS IN PRISTIONCHUS STENOCEPHALUS"

Sommer RJ

[International C. elegans Meeting, 1995]

During C. elegans vulva development, an equivalence group of six cells is recruited from 12 P-ectoblasts in the ventral cord. The size of the equivalence group changes during nematode evolution in members of three distinct families. Programmed cell death of seven cells (P(1-4, 9-11).p) reduces the number of Pn.p-ectoblasts to five, four of which are located in the central body region. In Poikilolaimus and Panagrolaimus all four remaining Pn.p-ectoblasts are vulva precursor cells.In Pristionchus (Diplogasteridae) the vulva is formed by P(5-7).p, whereas the remaining ectoblast P8.p, is not competent to adopt vulval fates. Thus, cell death and change of competence restrict the vulva equivalence group, and only the three cells that normally form the vulva, P(5-7).p, are competent to do so. To analyze the genetic control of Pn.p-ectoblast specification we isolated mutants with defects in Pn.p-ectoblast determination in Pristionchus. Two classes of mutations, where the two anterior cells, P(3,4).p survive have been observed. In one class, these cells are competent to respond to inductive signal, therefore constituting an equivalence group. In the second class, the two additional Pn.p-ectoblasts along with the normal vulva precursor cells form vulval tissue in the absence of inductive signal. In a third class of mutations the more posterior Pn.p-ectoblasts, P(9-11).p can survive and form vulva-like structures in an AC independent manner. Based on the described mutant phenotypes we hypothesize that the restriction of the vulva equivalence group in Pristionchus is a derived character.

Sommer RJ et al. (1993) International C. elegans Meeting "Evolutionary analysis of vulva development in different nematode species."

Sommer RJ, Carta LR, Sternberg PW

[International C. elegans Meeting, 1993]

Sommer RJ et al. (1994) Worm Breeder's Gazette "Evolution of Vulva-Formation: Part II: Species With a Central Vulva"

Sommer RJ, Sternberg PW

[Worm Breeder's Gazette, 1994]

Evolution of vulva-formation: Part II: Species with a central vulva Ralf J. Sommer & Paul W. Sternberg, California Institute of Technology, Division of Biology 156-29, Pasadena, CA 91125

Sommer RJ et al. (1994) Worm Breeder's Gazette "Evolution of Vulva Formation: Part IV: Variation in AC Position Can Cause a Shift of Vulva Formation Towards P(4-6).p."

Sternberg PW, Sommer RJ

[Worm Breeder's Gazette, 1994]

Evolution of vulva formation: Part IV: Variation in AC position can cause a shift of vulva formation towards p(4- 6).p Ralf J. Sommer & Paul W. Sternberg, HHMI & California Institute of Technology, Division of Biology 156-29, Pasadena, CA

Ralf J. Sommer (2005) WormBook "Evolution of development in nematodes related to C. elegans."

Ralf J. Sommer

[WormBook, 2005]

The knowledge about C. elegans provides a paradigm for comparative studies. Nematodes are very attractive in evolutionary developmental biology given the species richness of the phylum and the easiness with which several of these species can be cultured under laboratory conditions. Embryonic, gonad, vulva and male tail development were studied and compared in nematodes of five different families, providing a detailed picture of evolutionary changes in development. In particular, vulva development has been studied in great detail and substantial differences in the cellular, genetic and molecular mechanisms have been observed between C. elegans and other nematodes. For example, vulva induction relies on the single anchor cell in C. elegans, whereas a variety of different cellular mechanisms are used in related species. In recent years, a few species have been developed as satellite systems for detailed genetic and molecular studies, such as Oscheius tipulae and Pristionchus pacificus.

Pires da Silva A et al. (2000) European Worm Meeting "Novel mutants defective in vulva induction in Pristionchus pacificus"

Sommer RJ, Pires da Silva A

[European Worm Meeting, 2000]

More than 50 genes involved in vulva development have been characterized in the rhabditid C. elegans. The extensive characterization of this model system provides a framework for studying the genetic basis of evolutionary modifications. Cell fate specification during vulva formation differs significantly between C. elegansand the diplogasterid nematode Pristionchus pacificus. Cell ablation experiments in P. pacificus demonstrate the existence of several novel cell-cell interactions (Sigrist and Sommer, 1999; Sommer and Sternberg, 1996). To understand the molecular mechanisms underlying vulval pattern formation in P. pacificus, we performed several TMP/UV and EMS mutagenesis screens. The mutants isolated in these screens fall into two categories: I) "generation-vulvaless" mutants do not generate Pn.p cells; II) "induction-vulvaless" mutants generate Pn.p cells, but these fail to differentiate. We have isolated and characterized a new class of induction vulvaless mutants, in which P6.p differentiates as a normal 1 cell, but P5.p and P7.p adopt a non-vulval fate (3). In wild type P. pacificus, as in C. elegans, P6.p adopts the 1 fate, whereas P5.p and P7.p generate the 2 lineage. Four mutants, tu114(TMP/UV), tu132(EMS), tu48(EMS) and tu51 (EMS), display this defect to different extents. Complementation test among these mutants are in progress. We are using a PCR-based genomic substraction strategy (RDA) to identify the deletion associated with the tu114 mutant. The identification of the genes involved in the induction of the vulva in P. pacificus may help us understand how molecular mechanisms change during evolution. Sigrist, C. B., and Sommer, R. J. (1999). Vulva formation in Pristionchus pacificus relies on continuous gonadal induction. Dev Genes Evol 209, 451-9. Sommer, R. J., and Sternberg, P. W. (1996). Apoptosis and change of competence limit the size of the vulva equivalence group in Pristionchus pacificus: a genetic analysis. Curr Biol 6, 52-9.

Sommer RJ et al. (2000) European Worm Meeting "Novel mutants defective in vulva induction in Pristionchus pacificus"

Pires da Silva A, Sommer RJ

[European Worm Meeting, 2000]

More than 50 genes involved in vulva development have been characterized in the rhabditid C. elegans. The extensive characterization of this model system provides a framework for studying the genetic basis of evolutionary modifications. Cell fate specification during vulva formation differs significantly between C. elegansand the diplogasterid nematode Pristionchus pacificus. Cell ablation experiments in P. pacificus demonstrate the existence of several novel cell-cell interactions (Sigrist and Sommer, 1999; Sommer and Sternberg, 1996). To understand the molecular mechanisms underlying vulval pattern formation in P. pacificus, we performed several TMP/UV and EMS mutagenesis screens. The mutants isolated in these screens fall into two categories: I) "generation-vulvaless" mutants do not generate Pn.p cells; II) "induction-vulvaless" mutants generate Pn.p cells, but these fail to differentiate. We have isolated and characterized a new class of induction vulvaless mutants, in which P6.p differentiates as a normal 1 cell, but P5.p and P7.p adopt a non-vulval fate (3). In wild type P. pacificus, as in C. elegans, P6.p adopts the 1 fate, whereas P5.p and P7.p generate the 2 lineage. Four mutants, tu114 (TMP/UV), tu132 (EMS), tu48 (EMS) and tu51 (EMS), display this defect to different extents. Complementation test among these mutants are in progress. We are using a PCR-based genomic substraction strategy (RDA) to identify the deletion associated with the tu114 mutant. The identification of the genes involved in the induction of the vulva in P. pacificus may help us understand how molecular mechanisms change during evolution. Sigrist, C. B., and Sommer, R. J. (1999). Vulva formation in Pristionchus pacificus relies on continuous gonadal induction. Dev Genes Evol 209, 451-9. Sommer, R. J., and Sternberg, P. W. (1996). Apoptosis and change of competence limit the size of the vulva equivalence group in Pristionchus pacificus: a genetic analysis. Curr Biol 6, 52-9.

Anderton SM et al. (1996) East Coast Worm Meeting "Comparisons of serotonin containing neurons in freeliving nematodes: correlation (or not) of ventral cord neurons with vulval precursor cell patterns."

Anderton SM, Loer CM

[East Coast Worm Meeting, 1996]

We are interested in how patterns of serotonergic neurons are specified in the nematode. In C. elegans, six hypodermal cells (P38.p) are competent to produce vulva in the central body of the hermaphrodite. In this same body region in the ventral nerve cord (VNC) of the male, P38.aap normally divide to produce two neurons, one of which contains serotonin (CP neurons, P38.aapp). We wondered whether related species of worms that have a different number of vulval precursor cells than C. elegans might also alter the pattern of serotonergic neurons in the male. We first examined Pristionchus pactficus which in the hermaphrodite has only 4 Pn.p ectoblasts, P58.p; anterior and posterior Pn.p cells undergo programmed cell death (R. Sommer, personal communication). We found four serotonin-immunoreactive (JR) CP-like neurons in male Pristionchus VNC, correctly positioned to be P58.aapp. In the hermaphrodite VNC, we saw four cells, two anterior and two posterior to the vulva, and appearing to innervate the vulval region. These are likely to be 7C cells, only four of which (P58.aap) survive in Pristionchus (R. Sommer, pers. comm.). VC cells in C. elegans occasionally stain with serotonin antisera. With this simple picture in mind of a correlation between Pn.p cell fates in the hermaphrodite and Pn.aapp fate in the male, we examined several other species of worms with varying numbers of Pn.p cells (Sommer & Sternberg, 1995, Dev. Biol. 167: 61; Sommer & Sternberg, 1994, Science 265: 114). The simple-minded hypothesis did not hold up beyond Pristionchus. Panagrolaimus, also with P58.p cells in the hermaphrodite, had 8 CP-like somas in the male VNC (4 faint in the anterior, 4 bright in the posterior). Essentially the same pattern was seen in the male Rhabditella, in which the hermaphrodite has 5 Pn.p cells (P48.p). Both Pelodera and Teratorhabditis (each with P48.p in the hermaphrodite), looked like C. elegans, with 6 CP-like cells in the male VNC. Each of these species sometimes showed other faintly staining somas, paired with the CP-like neurons. Similar cells are sometimes seen in C. elegans and are believed to be CA neurons (Pn.aapa). We will present a complete pattern of serotoninIR cells in males and hermaphrodites for each of these species. We wish to thank Ralf Sommer for providing the non-C. elegans strains used and sharing unpublished information about them. Another undergraduate, Nicole Hinson, did the first staining with Pristionchus during a summer HHMI fellowship.

Knoch Lars et al. (2003) International Worm Meeting "Functional comparison of the EGF-like gene let-23 between Caenorhabditis elegans and Pristionchus pacificus"

Ralf Sommer, Knoch Lars

[International Worm Meeting, 2003]

Our lab studies the evolution of cell fate specification by comparing P. pacificus and C. elegans using vulva development as a model system. The comparison of loss of function mutations in orthologous genes between P. pacificus and C. elegans indicated substantial differences in gene function. To complement the genetic approach, we have used in vivo assays to analyze functional similarities and dissimilarities of orthologous proteins in C. elegans mutant backgrounds. Initial work with the two Hox genes lin-39 and mab-5 indicated that the P. pacificus genes can substitute for the C. elegans orthologs despite their functional differences (Grandien & Sommer, 2000; Gutierrez et al, 2003). To extend this work, we started to investigate components of the EGF/RAS/MAPK signal transduction pathway that mediate vulva development in C. elegans. In particular, we want to concentrate on the P. pacificus let-23 gene, the receptor tyrosine kinase that responds to the inductive signal from the LIN-3 ligand. Besides its role in vulva development, LET-23 also affects viability, male spicule formation, posterior development of the epidermis, and ovulation (Aroian and Sternberg, 1991). We cloned Ppa-let-23 using degenerate PCR and showed that the functional domains of LET-23 evolved differently from one another. For example, the C-terminal part of Ppa-LET-23 lacks three of the eight tyrosine-motifs involved in autophosphorylation and transduction important for individual Cel-LET-23 functions (Lesa and Sternberg, 1997). While one of these tyrosine motifs does not play any major role in C. elegans, the other two motifs have a strong effect on viability and vulva differentiation in C. elegans. We are currently testing the Ppa-let-23 cDNA for rescue of a Cel-let-23 mutant and planning further experiments with hybrid molecules between the let-23 genes of P. pacificus and C. elegans. AROIAN and STERNBERG, Genetics 128;251-267 (1991) LESA and STERNBERG, Mol. Biol. Cell 8:779-793 (1997) GRANDIEN & SOMMER, Genes Dev. 15:2161 -2172 (2001) GUTIERREZ et al., Development 130:983-993 (2003)

Kwang-Zin Lee et al. (2001) International C. elegans Meeting "Programmed cell death in Pristionchus pacificus"

Kwang-Zin Lee, Ralf J Sommer

[International C. elegans Meeting, 2001]

To study the evolution of developmental processes, we analyse vulva development in P. pacificus and compare it to C. elegans . In P. pacificus , 7 of the 12 ventral epidermal cells undergo apoptosis, whereas the corresponding cells in C. elegans fuse with the surrounding hypodermis. Phylogenetic analysis suggests that cell death of these epidermal cells represents a derived character. To understand the evolutionary changes responsible for these evolutionary alterations in the apoptotic mechanism, we are characterising cell death mutants in P. pacificus . Mutations in the cell death pathway in P. pacificus lead to the survival of P(1-4,9-11).p, which normally die in wild-type. Complementation tests have shown, that these mutants fall into two complementation groups, one of which has been proven to correspond to Ppa-ced-3 (Sommer et al., 1998). The second complementation group has been originally characterized as ipa-2 ( i nhibitor of P -ectoblast a poptosis) and is a good candidate for the Ppa-ced-4 homolog. To test this hypothesis, we tried to clone ced-4 using different approaches, viz low stringency hybridisation, PCR and yeast two hybrid approach with Ppa-mac-1 as bait. In C. elegans it has been shown that MAC-1, a member of the AAA type ATPase family, interacts with ced-4 at the protein level (Wu et al., 1999). However none of the used approaches were successful. We are presently trying to clone Ppa-ced-4 using positional cloning. Preliminary data suggest a linkage of ipa-2 and Ppa-pal-1 . In C. elegans , pal-1 is closely linked to ced-4 . Further mapping is in progress to clone P. pacificus ced-4 by chromosomal walking. Ref.: Sommer et al., Development 125 , 3865-3873 (1998) Wu et al., Development. 126 , 2021-2031 (1999)