Felix M-A et al. (1996) Nature "Sinistral nematode population."

Sternberg PW, Felix M-A, De Ley P

[Nature, 1996]

Several animal taxa display a consistent left-right asymmetry of the body plan. In nematodes, dextrality predominates. However, we have now found a nematode species that has sinistral populations.

Felix M-A (1999) J Exp Zool "Evolution of developmental mechanisms in nematodes."

Felix M-A

[J Exp Zool, 1999]

The recent findings that key developmental genes are conserved across animal phyla have led to descriptions of evolutionary change in development based on the recruitment of these few molecules. This approach, however, encounters problems in assigning homology across long evolutionary distances. By contrast, reproducibility of the cell lineage of free-living soil nematodes (order Rhabditida) and conservation of larval blast cells across nematode species permit evolutionary comparisons of developmental mechanisms among nematodes at the cellular level. Such comparative studies uncover an unexpected flexibility of developmental mechanisms: Large evolutionary differences have been described between invariant and noninvariant lineages, in the cellular mechanisms specifying a given cell (for instance, the gonadal anchor cell), in the subcellular events leading to asymmetric divisions (for instance, the first division of the egg), and in redundant networks of cell interactions (for instance, those specifying the centered pattern of vulva precursor fates). Interestingly, redundancy of developmental mechanisms favored by selective pressure allows in turn for evolution of these mechanisms. Such evolutionary changes in developmental mechanisms specifying cell fates can occur in the absence of obvious morphological change, which rather correlates with evolution of cell fates per se: death, division, migration, and differentiation (for instance, in the reduction of the posterior gonadal arm in monodelphic species or in change in vulva position).

Felix M-A (1997) M S-Medecine Sciences "One worm, 959 cells and 13,000 genes."

Felix M-A

[M S-Medecine Sciences, 1997]

The molecular pathways specifying cell fates during development are identified in the nematode Caeno-rhabditis elegans by the combination of genetic and molecular methods. For example, the differentiation of vulval precursor cells is induced by a signal similar to mammalian EGF, sent by the anchor cell of the gonad. This signal is received by a tyrosine kinase receptor and transmitted to the transcription factors in the nucleus through a very conserved molecular cascade. In mammals many components of this cascade, like Ras, are proto-oncogenes. At the cellular level, the reproducibility of C. elegans development and the possibility to selectively kill cells with a laser, allow the description of development in terms of cell interactions land asymmetric divisions. These developmental mechanisms can be ,compared in other nematode species: whereas molecular cascades are very conserved (even as far as mammals), modes of cell specification vary extensively (among nematodes).

Felix M-A et al. (2000) European Worm Meeting "Vulva development in oscheius Sp."

Louvet-Vall S, Felix M-A, Dichtel ML

[European Worm Meeting, 2000]

The vulva patterning mechanism is not conserved in all nematodes. We have started a genetic analysis in Oscheius/Dolichorhabditis CEW1, and about 60 vulva mutants have been isolated in an F2 Egl screen. The vulva lineage in this species is simple: P(5-7).p form the vulva; the central cell, P6.p, divides three times and then acquires the inner fate characterized by a "tttt" lineage. After two divisions, P5.p and P7.p acquire the outer vulval fate characterized by a "uuuu" lineage. P4.p and P8.p belong to the competence group but in normal development they divide two times and then acquire a non-vulval fate characterized by a "ssss" lineage. We found several mutants affecting the number of vulva cell divisions, irrespective of fate induction. 1) Some have defects only in P4.p and P8.p cells which divide too few times. Laser ablation studies in these mutants indicate that the correct number of divisions of P(5-7).p depends on a gonadal signal; in one mutant, the vulva fate and the number of divisions can be uncoupled while they are coupled for the other mutants [unpublshed data, Mark Viney and Paul W. Sternberg]. Moreover, it seems that the defect of division of P4.p and P8.p is correlated to a difference of these cells to respond to the anchor cell signal. It is interesting to note that in some natural populations of Oscheius Dolichorhabditis sp., P4.p and P8.p divide also too few times. 2) In other mutants, the defect of division affects all P(4-8).p which divide too few times. They appear to omit the second cell cycle in all lineages. 3) Some other mutants show an excess of P(5-7).p divisions: we observe a 3rd round of division for P5.p and P7.p and a 4th round in the P6.p lineage. All these phenotypes are unknown in C. elegans. We found also many mutants with a defect in the competence group and/or centering of the vulva. 4) In some, P(4-8).p behave like non-competent Pn.ps (lin-39 or bar-1 phenotype in C. elegans). 5) The competence group is enlarged to P3.p. 6) The competence group is enlarged to P9.p but some cells within the group are non-competent. Moreover, the vulva is miscentered on P5.p (this phenotype is unknown in C. elegans). 7) The vulva is miscentered on P7.p without modification of the competence group. This spectrum of vulva mutations is very different from that of C. elegans and also suggests that the relation between vulval cell cycle and fate differs from that of C. elegans.

Felix M-A et al. (1997) Development "Two nested gonadal inductions of the vulva in nematodes."

Sternberg PW, Felix M-A

[Development, 1997]

How do intercellular signals that pattern cell fates vary in evolution? During nematode vulva development, precursor cells acquire one of three fates in a pattern centered around the gonadal anchor cell. Non-vulval fates are at the periphery, outer and inner vulval fates are towards the center. In Caenorhabditis elegans, the three fates are specified around the same time by an induction by the anchor cell and lateral signaling between the vulva precursor cells. We find that, in three other nematode species (Panagrolaimus, Oscheius and Rhabditella spp.) spanning two families, the centered pattern is obtained by two temporally distinct gonadal inductions. The first induction specifies vulval fates; the second induction specifies the inner vulval fates in a subset of the precursors' daughters. This evolutionary change in the spatiotemporal connectivity of cell interactions allows centering of the pattern between two precursors in Panagrolaimus.

Felix M-A et al. (1999) Worm Breeder's Gazette "Microbacterium nematophilum -- not just a Cambridge disease"

Kuwabara PE, Felix M-A, Hodgkin JA

[Worm Breeder's Gazette, 1999]

A novel coryneform bacterial pathogen of C. elegans has been isolated twice at MRC-LMB, in 1986 and 1997, as a chance plate contaminant (see WBG 15.1, p. 73). 16S rRNA sequencing has now been carried out on these isolates and confirms their assignment to the genus Microbacterium. Previous typing, based on phenotypic characters, was generously carried out by Dr. Guido Funke (University of Zurich) who assigned them to the genus Aureobacterium, recently incorporated into the genus Microbacterium. The two isolates (CBX103 and CBX102) are 100% identical in 16S rRNA sequence, and 97-98% identical to eight other species of Microbacterium. The sequence divergence and distinctive properties of the pathogen justify definition of a new species, which has been named Microbacterium nematophilum.

Felix M-A et al. (2000) Nematology "Comparative developmental studies using Oscheius/Dolichorhabditis sp. CEW1 (Rhabditidae)."

Delattre M, Felix M-A, Dichtel ML

[Nematology, 2000]

In order to study the evolution of nematode vulva development, we focus on Oscheius/Dolichorhabditis sp. CEW1 (Rhabditidae) in comparison with Caenorhabditis elegans. In this species, the fates of the vulval precursor cells are determined by two successive nested inductions by the uterine anchor cell (instead of a single one in C. elegans). This hermaphroditic species can be cultured and handled like C. elegans. We review vulva development in this species. We present some molecular tools and the sequence of the Ras gene. This species is amenable to genetic analysis and we discuss the isolation of morphological markers.

Felix M-A et al. (1996) Worm Breeder's Gazette "Two-stage Induction of the Vulva in Panagrolaimus and Oscheius"

Sternberg PW, Felix M-A

[Worm Breeder's Gazette, 1996]

In Caenorhabditis elegans, P3.p to P8.p are competent to form the vulva, and in wild type development only P5.p to P7.p, centered around the anchor cell, actually do form the vulva. The central cell, P6.p, acquires a specific fate, revealed in particular by the TTTT lineage of its 4 granddaughters. The patterning of the Pn.p fates occurs via multiple interactions: an inductive signal from the anchor cell, lateral signalling between the Pn.p cells and negative signalling, presumably from the surrounding epidermis. Induction occurs in early L3, before they divide (Kimble (1981), Dev. Biol. 87, 286-300, and M. Wang and P.W.S., unpublished). In the family Panagrolaimidae, the anchor cell is positioned between P6.p and P7.p, and the 'TTTT' inner fate is shared between their 2 central daughters, P6.pp and P7.pa. By ablating the gonad or the anchor cell in Panagrolaimus PS1732 at different times, we found two temporally distinct signals acting on the Pn.p cells: the first one originates from the gonad, in early L2 (when the gonad precursors Z1 and Z4 have not yet divided- they divide late in L2 in this species). This first signal induces the Pn.p cells to divide twice in late L3 and form vulval tissue. The second inductive signal, in late L3, originates from the anchor cell and induces the central daughters of the Pn.p cells (P6.pp and P7.pa) to divide twice more instead of only once ('TT' inner fate).

Felix M-A et al. (1996) Development "Symmetry breakage in the development of one-armed gonads in nematodes."

Sternberg PW, Felix M-A

[Development, 1996]

Whereas the hermaphrodite gonad of Caenorhabditis elegans has two symmetric arms (didelphy), the female/hermaphrodite gonad of many nematode species features a single anterior arm (monodelphy). We examined how gonadal cell lineages and intercellular signalling evolve to generate these diverse structures. In C. elegans, the two arms develop symmetrically from two somatic precursor cells, Z1 (anterior) and Z4 (posterior). Each first gives rise to one distal tip cell (which promotes arm growth and germ line proliferation), two ovary precursors and three uterine precursors in the center of the developing gonad. In monodelphic species, Z1 and Z4 have different fates. The first visible asymmetry between them is in the relative timing of their divisions, followed by asymmetric cell movements. The putative posterior distal tip cell is then eliminated in all but one species by programmed cell death. In some species the posterior ovary precursors form a small vestigial posterior arm, the post-vulval sac; in other species, they stay undivided, or die. In Cephalobus sp. PS1197, the specific fate of Z4 progeny is induced by Z1 (or its daughters). In the uterus in C. elegans, symmetric lateral signalling between Z1.ppp and Z4.aaa renders them equally likely to become the anchor cell, which links the uterus to the vulva. In the different monodelphic species, anchor cell specification is biased, or fully fixed, to a descendant of either Z1 or Z4. Replacement regulation upon anchor cell ablation is conserved in some species, but lost in others, leading to a mosaic-type development. Differentiation between Z1 and Z4 is thus manifested at this later stage in the breakage of symmetry of cell interactions in the ventral uterus.

Felix M-A et al. (1997) International C. elegans Meeting "Evolutionary variations in nematode vulva patterning mechanisms"

Viney ME, Sternberg PW, Felix M-A

[International C. elegans Meeting, 1997]

To understand how developmental mechanisms vary during evolution, we compared vulva development of different nematode species and have initiated genetic analyses in one species other than C. elegans. During vulva development, Pn.p precursor cells are aligned in the ventral cord and acquire one of three fates in a symmetric pattern centered around the gonadal anchor cell: non-vulval fates at the periphery, outer and inner vulval fates towards the center. In C. elegans, the pattern is centered on P6.p. The three fates are specified around the same time by cell interactions: a graded induction by the anchor cell and lateral signaling of P6.p to P5.p and P7.p. We find that in three other nematode species spanning two families, the centered pattern is obtained by two temporally distinct inductions. The first induction specifies vulval vs. non-vulval fates, the second, localized to a subset of the daughters of the vulva precursors, specifies inner vs. outer vulval fates. In Panagrolaimus, the pattern is centered between P6.p and P7.p, the vulva is formed from four precursor cells (P5.p to P8.p) and the inner vulval fate is shared between P6.pp and P7.pa. In Oscheius and Rhabditella, the pattern is centered on P6.p as in C. elegans, but a late induction by the anchor cell on P6.pa and P6.pp is required for the proper specification of inner fates. Variation of the spatio-temporal connectivity of cell interactions may thus occur but nonetheless result in the same global pattern of cell fates. To understand the molecular nature of the 2 signals from the anchor cell and their relation with the pathways known in C. elegans, we have started a genetic and molecular analysis of 2-step vulva induction in Oscheius n. sp. CEW1. So far, we have isolated in a random F2 screen several vulva mutations and 35 marker mutations (a spectrum similar to C. elegans). The first characterized vulva mutation (sy447) affects the first induction only: the outermost cells adopt the outer vulval fate instead of a non-vulval fate. We are also developing molecular tools in this species, such as a cDNA library and transformation, and cloning homologs of molecules involved in vulva induction in C. elegans, such as LIN-3 and Ras.