Worm Breeder's Gazette 13(2): 91 (February 1, 1994)
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.
We are interested in understanding how ectodermal cell fates are specified. lin-26 is a gene that we think is necessary to specify the fates of hypodermal and neural support cells (Labouesse, Hartwieg, Sookhareea and Horvitz, to be submitted). Last year at the C. elegans meeting, we presented a brief description of the LIN-26 protein expression pattern during embryogenesis. In short, using antibodies against the LIN-26 protein we determined lin-26 to be expressed in all hypodermal cells, all support cells associated with sensory organs, in the somatic gonad precursors and in the germline (Labouesse et al., to be submitted). Depending on the type of cell, we observed the LIN-26 protein to be first expressed at different periods of the lineage history of each cell.
l) The LlN-26 protein was first detected in the germline of gravid adults and the protein, and was next detected in the germline lineage of embryos (Pl, P2 , P3 , P4 and Z2 /Z3),suggesting a maternal expression of the gene.
2) In cell lineages that generate the body hypodermis, we believe that expression was initiated two cell divisions prior to the generation of these cells at 240 minute of development; this was based upon number of cells stained after the 80-cell stage and position relative to the germline founder cells.
3) In cell lineages that generate the rectal cells and tail hypodermal cells, we first detected lin-26 expression in the immediate precursors of these cells, thus one cell division prior to the generation of these cells; this was based upon direct identification of the precursors by comparison with published fate maps.
4) In cell lineages that generate the excretory cell, excretory duct cell, excretory socket cell, head hypodermal cells and neural support cells, we detected expression in the corresponding cells immediately after their generation (possibly for some immediately prior to the division of the precursor).
5) Expression in the cells that generate the somatic gonad (Z1 and Z4 ),expression was initiated three hours after the cells had been generated and two hours after they had reached their final positions.
For a somewhat unrelated purpose, we wished to work out in situ hybridization conditions. We thought that it would be helpful to use as a probe a gene for which the expression pattern is known, and thus chose lin-26 as a test gene. Knowing the LIN-26 protein expression pattern, the lin-26 RNA expression pattern still proved to be interesting. We used a slightly modified version of the in situ hybridization protocol devised by Seydoux and Fire (C. elegans 1993 Meeting abstract p. 403; thanks Geraldine for the protocol). Still preliminary analysis of embryos stained with a lin-26 antisense probe labeled with digoxygenin indicates that the spatial expression pattern of the lin-26 RNA and the LIN-26 protein are essentially identical in all lineages examined (germline, hypodermis and support cells), although there might be minor differences. In particular at early stages of zygotic expression (body hypodermis lineages), we did not detect the lin-26 in more cells than the LIN-26 protein. If confirmed it would mean that descendants of the AB blastomere acquire their fate quite early. However, there is a major temporal difference. The lin-26 RNA was expressed more strongly in precursors than in differentiated cells, and could in fact hardly be detected after the cells that differentiate had been generated. For instance the abundance of the lin-26 RNA was generally very low in cells of the body hypodermis after the lima bean-stage of development. By contrast, the abundance of the LIN-26 protein was lower in precursors than in differentiated cells, and it remained very abundant in differentiated cells. It might be not surprising that the RNA is unstable or not expressed once cell proliferation is over.