Embryological variation during nematode development

Abstract

Early cell lineages and arrangement of blastomeres in C. elegans are similar to the pattern found in Ascaris and other studied nematodes leading to the assumption that embryonic development shows little variation within the phylum Nematoda. However, analysis of a larger variety of species from various branches of the phylogenetic tree demonstrate that prominent variations in crucial steps of early embryogenesis exist among representatives of this taxon. So far, most of these variations have only been studied on a descriptive level and thus essentially nothing is known about their molecular or genetic basis. Nevertheless, it is obvious that the limited morphological diversity of the freshly hatched juvenile and the uniformity of the basic body plan contrast with the many modifications in the way a worm is generated from the egg cell. This chapter focuses on the initial phase between egg activation and gastrulation and deals with the following aspects: reproduction and diploidy, polarity, cleavage and germ line, cell lineages; cell cycles and maternal contribution, cell-cell communication and cell specification, gastrulation.

Morphological evolution and embryonic developmental diversity in metazoa

“…There is some variation in the orientation of the early cleavage events among nematodes, but given that these differences occur mainly between only distantly related nematode clades, one can postulate that early nematode development is rather conserved (Schierenberg, 2006) when compared with that of arthropods or vertebrates. For example, among all the nematodes studied, only one species displays gastrulation occurring through the introgression of a large number of cells (Schierenberg, 2005), as is normally the case in echinoids, another type A developer.…”

Development and Cell Polarity of the C. elegans Intestine

“…In brief, these events include the correct specification and asymmetric division of the intestinal founder cell EMS (Bossinger and Schierenberg, 1996;Goldstein, 1992;Han, 1997;Kormish et al, 2010;Schierenberg, 1987;see Fig.2 for further details), the ingression of the intestinal precusor cell Ea and Ep during gastrulation ( Fig.5B-C ;Chisholm, 2006;Putzke and Rothman, 2003;Rohrschneider and Nance, 2009;Sawyer et al, 2009;Schierenberg, 2005;Schierenberg, 2006), the cytoplasmic polarization of intestinal primordial cells ( Fig.5D; Achilleos et al, 2010;Bossinger et al, 2001;Leung et al, 1999;Totong et al, 2007), the formation of apical adherens junction and the generation of the future lumen within the primordium (Fig.5E'-E''; Leung et al, 1999), the intercalation of specific sets of cells (Hoffmann et al, 2010;Leung et al, 1999), the invariant 'twist' in the anterior of the intestinal primordium (Hermann et al, 2000), and finally the differentiation of the late embryonic, larval and adult intestine that has been proposed to be under the control of the GATA-factor ELT-2 (McGhee et al, 2009;McGhee et al, 2007;Pauli et al, 2006).…”

The embryonic cell lineage of the nematode Halicephalobus gingivalis (Nematoda: Cephalobina: Panagrolaimoidea)

“…• C using a 4D microscope (Schnabel et al, 1997;Houthoofd et al, 2003). Every 30 s, 25 focal planes were recorded through the embryo and stored on a laser videodisk.…”

“…The lineage and 3D displays of each recording were reconstructed using the Simi Biocell software equipped with an automatic collision manager (version 3.5, 4.0, Simi, Unterschleissheim, Germany) (Schnabel et al, 1997). This collision manager automatically detects whether other nuclei are present close to a newly fixed nucleus and greatly reduces the error rate.…”

“…Most of this research focuses on specific phases or areas of development, such as early development (reviewed in Schierenberg, 2006) or development of the gonad, vulva and male tail (reviewed in Sommer, 2005). Until recently, no detailed, complete description of the embryonic development of any nematode other than C. elegans has been available (Sulston et al, 1983).…”