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.
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]