Worm Breeder's Gazette 12(5): 51 (February 1, 1993)
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.
The decision between the AC and VU fates.
In the somatic gonad of the hermaphrodite, four cells have variable fates: Z1 pW and Z4 aaa can adopt either the anchor cell (AC) or a ventral uterine precursor cell fate (VU3); and Z1 ppa and Z4 aap can adopt one of two ununique ventral uterine cell fates (VU1 or W2 )(Kimble and Hirsh, 1979). Laser ablatlon experiment in the late L2 stage have demonstrated that the fates of the four cells are determined by cell-cell interactions, and have suggested that Z1 .pppand Z4 .aaa form one equivalence group (the AC/VU3 equivalence group) and that Z1 ppa and Z4 .aap form another equivalence group (the VU1 /VU2equivalence (group) (Kimble, 1981).
We have done additional ablation experimentsa and found that Z1 .ppa, Z1 ppp, Z4 .aaaand Z4 .aapappear to be equivalent in the early L2 stage in that they all have the potential to be an AC or a VU: if Z1 .pppand Z4 .aaaare ablabted 1-3 hrs after their birth (L1-L2 molt), either Z1 .ppaor Z4 .aapcan adopt the AC fate (5/7 operated hermaphrodites had an AC). In the early L2 stage, the potential for Z1 .ppaand Z4 .aapto become an AC in the absence ot Z1 .pppand Z4 .aaarapidiy decreases (only 5/16 operated hermaphrodites had an AC). By the Iate L2 stage, this potential is gone (0/9; also see Kimble, 1981) Iin-12 activity is required for Z1 .ppaand Z4 .aapto loss the potential to adopt the AC fate in lin-12 (0)hermaphrodites, Z1 .ppaand Z4 .aapretain this potential until the L2 -L3molt [7/11 opened lin-12 ( n941 )hermaphrodites had an AC].
We conclude that Z1 .ppa, Z1 .ppp, Z4 .aaaand Z4 .aapmust all decide between the AC and VU fates and that this decision involves lin-12 activity A difference among the four cells, however, is that Z1 .ppaand Z4 .aapcommit to a VU fate earlier than their sisters. One possibility is that Z1 .ppaand Z4 .aapaccumulate lin-12 activity faster than their sisters so as to hrm a VU1 /VU2equivalence group with high lin-12 activity while Z1 .pppand Z4 .aaaform a distinct, AC/VU3 equivalence group with lower lin-12 activity. However, another lin-12 independent mechanism must also be operating since in the absence of lin-12 Z1 .ppaand Z4 .aapoften still adopt a VU fate, while Z1 .pppand Z4 .aaanever do (Greenwald et al, 1983).
The role of the AC in vulval morphogenesis
Laser ablation experiments have shown that the AC is required in the early L3 stage for vulval induction, for the formation of a correctly shaped vulval invagination, and for the attachment of the vulva to the uterus to form an opening for egg laying (Kimble, 1981). We have ablated the AC at later times in vulval development to examine Iater requirements for the AC in vulval morphogenesis. We first ablated the AC after the vulval precursor cells had divided once (ie after vulval induction had occurred; Sternberg and Horvitz, 1986). None of the 11 operated hermaphrodites were able to lay eggs normally, consistent with the results of Kimble (1981). In addition, 9 of 11 hermaphrodites developed a protruding vulva. In all operated hermaphrodites examined, vulval invagination was normal, including the formation of a wild-type "Christrnas tree" structure in the L4 stage. We therefore believe that the vulval protrusion is the result of abnormal vulval eversion. The ablaffon of other cells in the somatic gonad, particularly uterine precursor cells, can also cause improper vulval eversion, but at a somewhat lower frequency. These results taken together suggest that the integrity of the somatic gonad is important for normal vulval eversion.
We then ablated the AC in the late L3 stage after all vulval cell divisions were complete and morphogenesis had begun, but before eversion occurred. Surprisingly, all 12 operated hermaphrodites had normal vulval eversion and were able to lay eggs. Thus, the AC is required for vulval eversion and passageway formation at an earlier time than when these events occur. One possibility is that the AC specifies the fates of the uterine and/or vulval precursor cells so that the conect descendants are generated and interact properly in the L4 stage. Alternatively, the AC may lay down an extracellular matrix during the L3 stage that guides later vulval morphogenesis and eversion.
Some ot these experiments have been described in more detail elsewhere (Seydoux et al, 1990 Cell 61 939-951; Seydoux et al, 1993 Dev Biol, in press).
Seydoux et al, 1993 Dev Biol, in press.