Worm Breeder's Gazette 14(3): 25 (June 1, 1996)

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.

Cephalobus spec. shows a different pattern of gut induction and differentiation

Oliver Wiegner, Einhard Schierenberg

Zoological Institute, University of Cologne, 50923 Cologne, Germany Gut induction is a well known example for cellular interaction in the early C. elegans embryo (Schierenberg, 1987; Goldstein, 1992). Contact between the germline cell P2 and the gut precursor cell EMS in the early 4-cell stage is necessary to specify the gut fate. As a consequence of the interaction, EMS divides into an anterior MS cell and a posterior E cell and the gut primordium is formed by the progeny of the latter. To understand more about the evolution of cell specification- mechanisms we decided to investigate gut differentiation in other soil nematodes. We chose Cephalobus spec. an apparently more primitive representative of rhabditid nematodes. Its embryogenesis differs considerably from that of C. elegans (Skiba and Schierenberg, 1992). These differences go along with a modified pattern of cell communication visualized by microinjected tracer dyes (Bossinger and Schierenberg,1996).

As shown recently (Bossinger et al., 1996), the developing gut in 
both species accumulates fluorescently labelled transferrin as a
marker for receptor-mediated endocytosis. We used this endocytotic 
property to assay gut differentiation in Cephalobus because it lacks
autofluorescence and birefringence of the gut granules as found in 
C. elegans and the antibody 1CB4 recognizes gut cells only in 
advanced embryos.
Although development of Cephalobus takes more than 5 times longer 
compared to C. elegans, gut differentiation becomes visible at a much 
earlier developmental stage. Cephalobus shows endocytosis of 
transferrin already from the 2E-cell stage (<50 cells) onwards, C. 
elegans only in the late 8E-cell stage (>300 cells). In order to test 
whether in Cephalobus gut differentiation depends on an induction by 
P2 as in C. elegans, we removed the germline cell directly after its 
birth through a laser-induced hole in the eggshell.
As expected, embryos developed into non-hatching monsters with 
several hundred cells expressing signs of cell differentiation like 
muscle twitching.
Surprisingly, gut differentiation was never affected: all P2- 
deprived embryos developed a gut primordium with strong endocytotic 
activity. Thus, gut differentiation in Cephalobus seems to be 
independent of interactions with germline cells. 
In contrast, removal of the AB cell in the 3-cell embryo (which 
corresponds to the early 4-cell stage in C. elegans, because P1 
divides before AB) interferes with gut differentiation. 
In most cases the AB blastomere was removed only partially, always 
including the nucleus together with varying amounts (40-100%) of 
cytoplasm. 2/3 (27 out of 40) embryos failed to develop gut 
However, 1/3 (13 out of 40) formed gut visualized by the accumulation 
of transferrin. These data suggest that in Cephalobus the AB cell 
may be responsible for gut induction.
By varying time and amount of cytoplasmic extrusions we are presently 
trying to better understand the observed variation. An intriguing 
hypothesis is that the establishment of intercellular communication 
via cytoplasmic bridges in the 3-cell stage (Bossinger and
Schierenberg,1996) might be required for gut induction in Cephalobus.
Bossinger, O.; Schierenberg, E. (1996). Develop., Genes, Evolut.
(formerly Roux's Arch. Dev. Biol.), in press.
Bossinger, O.; Wiegner, O.; Schierenberg, E. (1996). Roux's Arch. 
Dev. Biol., in press.
Goldstein, B. (1992). Science 357: 255-257.
Schierenberg, E. (1987). Dev. Biol. 122: 452-463.
Skiba, F; Schierenberg, E. (1992). Dev. Biol. 151: 597-610.