Early embryogenesis of the pinewood nematode Bursaphelenchus xylophilus

Abstract

The early embryogenesis and cell lineage of the pinewood nematode Bursaphelenchus xylophilus was followed from a single-cell zygote to a 46-cell embryo under Nomarski optics, and elongation of the microtubules was studied by immunostaining. As a B. xylophilus oocyte matures, it passes through a passage connecting the oviduct with the quadricolumella, the distal part of the uterus, and reaches the quadricolumella where it stays for a few minutes and is fertilized. After fertilization, the germinal vesicle disappears, an eggshell is formed, and the male and female pronuclei appear. The pronuclei move toward each other and fuse at the center of the egg. Around this time, the microtubule-organizing center appears. The presumptive region of sperm entry into the oocyte becomes the future anterior portion of the embryo. This anterior-posterior axis determination is opposite to that of Caenorhabditis elegans, where the sperm entry site becomes the posterior portion of the embryo. The optimal growth temperatures of these two nematodes also differ in that temperatures of about 30 degrees C afford the fastest growth rate and highest hatching frequency in B. xylophilus. Otherwise, the lineage resembles that of C. elegans with respect to timing, positioning and the axis orientation of each cell division.

Polarity of the ascidian egg cortex and relocalization of cER and mRNAs in the early embryo

“…This suggests that ascidians species separated by millions of years of evolution share the same cellular and molecular mechanisms to establish developmental axes and translocate and segregate determinants acting on posterior blastomeres in similar ways. Such conservation does not seem to have happened in nematodes, which show great flexibility in cellular mechanisms of sperm-directed axis formation and domain localization (P granules) (Goldstein et al, 1998;Hasegawa et al, 2004). Our previous experiments with Halocynthia strongly suggested that there was a link between the cER network established in the oocyte and the CAB, the macroscopic cortical structure mediating unequal posterior cleavages, which acts as a signalling centre for muscle and posterior development (Nishida, 2002a;Nishida, 2002b).We did not, however, investigate whether the cER-mRNA domain that moved posteriorly was retained as part of the isolated posterior cortex.…”

Acto-myosin reorganization and PAR polarity inC. elegans

“…In many polarized embryos, there is a general consensus regarding the signal: the site of fertilization and the sperm-contributed centrosomes establish the initial axis (Astrow et al, 1989; Carre and Sardet, 1984; Dondua et al, 1997;Eckberg, 1981;Fernandez et al, 1998;Freeman, 1978;Hable and Kropf, 2000;Hasegawa et al, 2004;Luetjens and Dorresteijn, 1998;Roegiers et al, 1995;Ubbels et al, 1983). Likewise, in C. elegans embryos, centrosomes are essential for polarity establishment (Cowan and Hyman, 2004b).…”

Chromosome structure and behaviour in Bursaphelenchus xylophilus (Nematoda: Parasitaphelenchidae) germ cells and early embryo

“…Because of the small chromosome size and cell-destructive preparation method for staining (squashing method), it has been very difficult to observe chromosome behaviour and determine the karyotype of this nematode. Bursaphelenchus xylophilus reproduces bisexually (amphimixis), and its early embryogenesis was previously described (Hasegawa et al, 2004). In this paper, we examined the chromosome behaviour in B. xylophilus during gametogenesis and early embryogenesis from fertilisation to the two-cell stage embryo, without squashing, by DAPI staining and confocal laser-scanning microscopy.…”

“…Despite its parasitic nature, B. xylophilus can be easily maintained in the laboratory feeding on plant calli or fungi (Iwahori & Futai, 1990). It has a large brood size with a short generation time (Mamiya, 1975) and is suitable for microscopy because of its simplicity and transparent body and embryo (Hasegawa et al, 2004). Transcriptional and functional analyses of B. xylophilus genes have been initiated by constructing ESTs (Kikuchi et al, 2004(Kikuchi et al, , 2005.…”