Worm Breeder's Gazette 12(2): 88 (January 1, 1992)
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.
Previous work has shown that induction plays a role in gut specification in C. elegans: Isolating the EMS cell early in the four cell stage prevents gut from differentiating, and gut differentiation can be rescued by recombining EMS with P2 ,but not by recombining EMS with ABa and/or ABp (1). The time when induction specifies gut was defined by determining how early EMS must be isolated in order to block gut differentiation.
In order to determine at what point the induction is no longer occurring, an EMS cell was isolated early in the four cell stage (more than ten minutes before it cleaved - gut will not have been specified by this time). After waiting some time, EMS (or its daughter cells) was recombined with P2 (or its daughter cells). If the induction was still occurring at this time, P2 would still be able to rescue gut differentiation in EMS. If, however, the induction was no longer occurring, P2 would have no rescuing effect. By varying the length of time that EMS is isolated from P2 ,the time at which the induction ends can be determined. Preliminary results may have revealed something about the mechanics of gut induction. In the figure shown below, the first bar represents a summary of the isolation experiments (when EMS is isolated more than ten minutes before it cleaves, gut doesn't differentiate; note that the EMS cell cycle takes 15-20 minutes in culture.) Each of the 10 bars below represents one case where an EMS was isolated early in the four cell stage, was left in isolation for some time, and then was placed back in contact with P2 .These cases define the time at which the induction ends as a few minutes before EMS cleaves (2). In addition, there is no overlap in the timing of positive and negative cases, suggesting that this time is fairly reproducible from one embryo to another. That P2 must contact EMS before EMS cleaves suggests that the induction may effect a cleavage stage specific event, such as the segregation of particular EMS contents into E or MS. Experiments are being done now to determine whether this time represents the time that P2 no longer induces or the time that EMS is no longer competent to respond to the induction.
[See Figure 1]
2. This result was surprising, as previous work on timing of inductions (as defined in vertebrates) shows that inductions take a long time (hours, generally) and the times they begin and end are not clearly defined in the embryo (Jacobson, A.G., Science 152:25-341966.)