The early embryonic development of the satellite organism Pristionchus pacificus: differences and similarities with Caenorhabditis elegans

Abstract

Summary -As a comparative counterpart for the model organism Caenorhabditis elegans, the nematode Pristionchus pacificus was established as a satellite organism to study developmental processes. However, these studies mainly focused on post-embryonic development and little is known about the early embryonic development. Using 4D microscopy we reconstructed the early embryonic cell lineage of 12 individuals of P. pacificus. By analysing several parameters of early development, including the division sequence, the spatial arrangement of blastomeres, the cell cycle patterns of the AB lineage and cell-cell contacts in different cell stages of the embryo, it was shown that the early embryonic development is nearly identical to C. elegans. Known cell-cell contacts necessary for induction of blastomere fates in C. elegans are also present in P. pacificus. Thus, the spatio-temporal conditions that would allow possible homologous inductions are present. However, at least one model for blastomere specification seems not to apply to P. pacificus since the third division in the AB lineage differs from that of C. elegans. Furthermore, naturally occurring variability of early development was demonstrated, which is clearly permitted since there seems to be no influence on further development into an adult worm.Keywords -4D microscopy, cell lineage, development, embryogenesis, Neodiplogastridae.In the last 10 years, the nematode Pristionchus pacificus Sommer, Carta, Kim & Sternberg, 1996 has been established as a satellite organism in evolutionary developmental biology (Eizinger et al., 1999;Sommer, 2000). For an overview of the biology of this nematode see Hong and Sommer (2006). Pristionchus pacificus belongs to the family Neodiplogastridae, a sister taxon of the family Rhabditidae that includes the model organism Caenorhabditis elegans. Comparative studies between P. pacificus and C. elegans have revealed differences in the regulation of developmental processes such as the development and genetic analysis of sex determination (PiresdaSilva & Sommer, 2004), vulva development (Sommer & Sternberg, 1994Sigrist & Sommer, 1999;Sommer, 2005) and gonad formation (Rudel et al., 2005;Sommer, 2005). For instance, cellular and molecular differences in vulva formation include different cellular interactions as well as different genetic interactions required for cell fate specification of vulval cells (see Eizinger et al., 1999;Sommer, 2000Sommer, , 2001Sommer, , 2005. Recently, developmental and molecular studies of P. pacificus have been * Corresponding author, e-mail: Gaetan.Borgonie@ugent.be complemented by genomic data comprising the genetic linkage map (Srinivasan et al., 2002), the physical map (Srinivasan et al., 2003), and whole genome sequencing, which is approaching completion. In addition, the ecology and the specific habitat/ecological niche of P. pacificus have been studied. Herrmann et al. (2006) showed that Pristionchus species are often associated with scarab beetles and the Colorado potato beetle. To interpret these ecol...

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