Worm Breeder's Gazette 11(1): 65

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Comparative Analysis of Early Embryogenesis in Different Free-Living Nematode Strains

Frauke Skiba and Einhard Schierenberg

Figure 1

We have collected soil from places as near as the institute backyard 
and as far as the mountains of Peru.  From these probes we have 
isolated different nematode strains and have cultured those which 
happened (or got used) to grow on our standard agar plates.  With the 
help of Dr.  Sudhaus, Berlin, we have characterized them 
phenotypically.  They probably represent 16 different species which 
all belong to the order 'Rhabditida'.  By the criteria of outer 
inspection one of them appears to be a 'C.  elegans', but a cross-
fertilization test needs to be done.  The adults of all strains are 
about 1-2 mm long and vary considerably in diameter.  Most of them 
express a life cycle several-fold longer than that of C.  elegans, 
none of them is faster.  About half of them are self-fertilizing 
hermaphrodites.  We have analyzed early cell lineages up to the 50-
cell stage and have compared them to those of C.  elegans.  All 
strains express the typical pattern of nematode cleavage, whereby 
somatic founder cells (AB,HS,E,C,D) are generated in a series of 
unequal germline cleavages.  In detail, however, variations were found 
which essentially concern the timing of cell divisions in the germline.
Those strains which come closest to C.  elegans in speed of 
developmental events also express the same sequence of early cleavages.
In those strains with a slower developmental rhythm, divisions in 
the germline cells P1- P3 take place relative too early.  In general, 
the following correlation was found: The slower embryogenesis proceeds 
in a certain strain, the earlier germline cleavages occur in the 
sequence of dividing blastomeres (see figure below).  In our slowest 
strain (Cephalobus spec.  from Peru) P4 is present already in the 6-
cell stage, compared to the 24-cell stage in C.  elegans.  Altered 
sequence of cleavages leads to early cell patterns different from 
those in C.  elegans.  By the 24-cell stage, however, spatial 
organization of cells has become essentially the same in all strains.  
Our findings are consistent with the view that germline cells have to 
cleave within a certain time limit to preserve (or obtain) their 
specific identity as suggested by the cib-mutants (R.  & H.  Schnabel, 
pers.  communication).  Testing with an antibody against C.  elegans P 
granules, we found that about 50% of the strains showed P granule 
staining.  So far, we have no indication that these results reflect 
phylogenetic relationships.  In no case we detected chromatin 
[See Figure 1]

Figure 1