Worm Breeder's Gazette 12(4): 35 (October 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.
During C. elegans hermaphrodite development, 131 of the 1090 somatic cells generated undergo programmed cell death. The gene ced-9 appears to play a central role in controlling this process. A gain-of-function mutation that activates ced-9 prevents the cell deaths that occur during normal C. elegans development. Conversely, mutations that inactivate ced-9 cause cells that normally live to undergo programmed cell death. Mutations in ced-3 and ced-4 ,which block essentially all programmed cell deaths, suppress this ced-9 (lf)phenotype, indicating that the loss of ced-9 function results in an inappropriate activation of the pathway for programmed cell death. These observations show that ced-9 activity is both sufficient and necessary to protect cells from programmed cell death. We proposed that the normal function of ced-9 is to protect cells that are scheduled to survive from undergoing programmed cell death (Hengartner, Ellis, and Horvitz, Nature 356, 494-499, 1992).
To understand better how ced-9 prevents programmed cell death, we have cloned ced-9 .RFLP mapping followed by micro-injection of cosmids and various subclones have localized ced-9 rescuing activity to a 6 kb. We have sequenced this rescuing fragment and have isolated cDNAs hybridizing to this region from the Barstead library. Sequencing of these cDNAs revealed that the putative ced-9 transcript contains an 846 bp ORF that could encode a 280 amino acid protein. The ced-9 protein sequence was then used to search protein databases. The protein in the databases that showed the most similarity to ced-9 was the product of the mammalian proto-oncogene bcl-2 :the ced-9 and human bcl-2 proteins show 23% identity over their entire sequence. ced-9 possesses the C-terminal hydrophobic tail thought to be important for bcl-2 localization (S. Korsmeyer; personal communication) or function (Alnemri et al., PNAS 89, 7295-7299,1992). One of the three introns in ced-9 is in the same position as one of the two introns in human bcl-2 .
Interestingly, the proposed function of the bcl-2 oncogene is identical to the function we proposed for ced-9 : bcl-2 is thought to be required to prevent cells from undergoing programmed cell death. For example, overexpression of bcl-2 prevents or delays the programmed death of immune cells following a variety of stimuli, such as removal of growth factors, treatment with glucocorticoids or irradiation with low doses of gamma rays. These similarities in both sequence and function suggest that bcl-2 could be the vertebrate homologue of ced-9 .We are currently testing this hypothesis in several ways. For example, can human bcl-2 prevent programmed cell death in worms? Could ced-9 function in mammals? The fact that human bcl-2 appears to be able to delay cell death in insects (Alnemri et al., op. cit.) makes these ideas not as far-fetched as they may seem.
It is tempting to speculate that not only ced-9 but in fact the whole cell death pathway has been conserved throughout evolution, and that therefore the molecular mechanism underlying programmed cell death might be essentially the same in organisms as diverse as worms and humans.
S. Korsmeyer; personal communication.
Alnemri et al., PNAS 89, 7295-7299,1992.