Worm Breeder's Gazette 11(4): 112

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.

Absent Reversal of Cleavage Polarity in a Free-Living Nematode

Frauke Skiba and Einhard Schierenberg

Figure 1

As reported in WBG 11(1) we have started a comparative analysis of 
embryogenesis in a number of free-living soil nematodes.  Besides 
other aspects we tested whether our strains all express the typical 
reversal of cleavage polarity in the germline cell P2.  While after 
the division of P0 and P1 the new germline cell comes to lie posterior 
of its somatic sister, it is the other way round after cleavage of P2 
and P3 (see scheme below; for details, see Schierenberg,1987, Dev.  
Biol.  122,452).
In the course of our studies we found two species in which this 
reversal of polarity does not take place.
One of these is Cephalobus spec. which belongs to the order 
Rhabditida as do all of our studied strains including C.  elegans (
only species of this order appear to survive under our standard 
laboratory conditions).  Cephalobus is slowest of all our strains.  
Its early development is 14x slower than C.  elegans (at 16 C).  
However, development accelerates with increasing temperature but never 
comes close to C.  elegans.  The maximal temperature at which we get 
well reproducing Cephalobus is 35 C (C.  elegans 26 C).
The fact that in Cephalobus the whole series of unequal germline 
cleavages is completed at the 6-cell stage (C.  elegans: 24-cells) has 
been shown in the above mentioned WBG.  Because of this altered 
division sequence but also because of the missing cleavage reversal in 
the germline (see scheme below) an unusual spatial pattern of cells is 
generated.  By compensating migrations a pattern similar to C.  
elegans is reached prior to gastrulation.
With the antibody L-416 against germline-specific P granules 
courtesy of Susan Strome) in Cephalobus nuclei in all somatic cells 
can be marked, while in the germline only the perinuclear region 
appears to react positively.
From the data we have collected we assume that Cephalobus represents 
a more primitive (original?) species than C.  elegans.Below a scheme (
drawn from a photo series) is given demonstrating the missing polarity 
reversal.  For better visualization some cells have been removed from 
the anterior pole of both embryos.
[See Figure 1]

Figure 1