Worm Breeder's Gazette 5(2): 39
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.
Laser ablation of post-embryonic cells in the somatic gonad has revealed some role for cell-cell interaction in determining cell lineages during gonadogenesis: 1) There are three examples in which cells can be influenced to follow a natural alternative fate. In hermaphrodites, the anchor cell can be replaced by its alternative precursor. In males, the linker cell can be replaced by its alternative precursor. And, in hermaphrodites, one of the ventral uterine precursors switches into its alternative pattern of cell division after ablation of its sister ( the unused potential anchor cell) after the regulation of its sister into the anchor cell fate 2) There are two examples in which a cell is influenced to reverse the polarity of its lineage without changing the pattern of divisions or the type of progeny produced. This has been called vectorial regulation. The first example involves ablation of one of the somatic progenitor cells (Z1 or Z4) after which a functional half gonad is made. The lineage alteration needed to make this half gonad reverses the polarity of part of a cell lineage that normally gives rise to only the left (or right) half of the dorsal uterus plus small parts of the left (or right) halves of the anterior and posterior spermathecae. A reversal of polarity in half the lineage generates both left and right sides of the anterior (or posterior) uterus and anterior (or posterior) spermatheca. The second example, seen in the ventral uterus, reverses the polarity of the entire lineage of one precursor which thereby compensates for the ablation of a different ventral uterine precursor. 3) There is one example of induction - the anchor cell is required for the second stage divisions of the ventral hypodermal precursors ( P5.p-P7.p) and for morphogenesis. The first stage divisions of the precursors (P8.p-P8.p) occur not only without the anchor cell, but also without the entire gonad as shown by John White. 4) There is one example in which the lineage change varies somewhat from animal to animal. The cell involved is a precursor to the sheath and spermatheca. The sheath sublineage is usually normal in these experiments, so the remaining comments refer to the spermathecal sublineage. It is possible to isolate one of the sheath-spermatheca precursor cells from the cells it would normally interact with in the somatic primordium before that precursor has been born during L1. For example, if Z4 and Z1.p are killed, the only remaining somatic cell is Z1.a. Z1.aa is a distal tip cell which becomes separated from its sister, Z1. ap, a sheath-spermatheca precursor. In two such experiments, the isolated precursor cell made 12 cells in its spermatheca sublineage. These two lineages, however were very different, one simply making more cells by amplifying the normal pattern and one altering its normal pattern from a stem cell-like pattern to a symmetrical pattern. The latter is reminiscent of a duplication. In two other animals, Z1. p and Z4.a were killed so that the two sheath-spermatheca precursors, Z1.ap and Z4.pa made up the entire somatic primordium. In these animals, both cells amplified their normal spermathecal pattern to make more cells than normal. In one final experiment, Z1.ap reverted to a simple stem cell pattern after ablation of the dorsal uterine precursors Z1.ap and Z4.pa. The ultrastructure of progeny produced by these abnormal spermathecal lineages is always typical of normal spermathecal cells. These results lead to the working hypothesis that the spermathecal lineage is basically a stem cell lineage, and that the division pattern is normally modified by interaction with neighboring cells to give the invariant lineage observed in untreated animals. It has been possible to determine at what point in development a cell must be ablated to effect a specific lineage change for some of the examples listed above: For the ventral uterine and linker examples of regulation, the cell must be killed before the cells become rearranged to form the somatic primordium. (This refers to both replacement and vectorial types of regulation). The somatic primordium is formed at L1 lethargus in males and at L2 lethargus in hermaphrodites. Thus, it seems that the physical rearrangement of the cells coincides with some developmentally critical event which serves to limit the developmental potential of the cells. The induction of the vulva by the anchor cell appears to depend on an interaction that can take place hours before the anchor cell dependent divisions. A vulva is formed in about 10% of the animals in which the anchor cell is killed shortly after the molt to L3, and it is formed in 100% of the animals if the cell is killed about 4hr later, at the same time as the first stage divisions occur. Ablation of the anchor cell between these times generates a high percentage of intermediate induction events. Often only one or a few of the progeny made from the first stage divisions divide further. This partial induction occurs with equal frequency in daughters of P5.p, P6.p, or P7.p so it does not seem to be centered around the anchor cell. In addition, it often occurs in two daughters that are separate and therefore makes two minivulvae, so it seems not to be a cooperative event.