Worm Breeder's Gazette 11(3): 74

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 Structure of the Developing Vulva in the L4

J.G. White, E. Southgate and D. Kershaw

Figure 1

Reconstruction of the cellular organization of the vulva and uterus 
from electron micrographs is often difficult in the adult due to the 
presence of unfixed eggs in the gonad and the tissue stretching and 
distortion that occurs following vulva eversion at the L4 moult.  We 
have found that late L4 animals are much easier to reconstruct and 
have undertaken a serial section reconstruction of the vulval and 
uterus.
The L4 vulval primordium is made up of a stack of seven, multi-
nuclear toroidal epidermal cells designated A, B1, B2, C, D, E & F (
the figure shows a transverse view of these cells to one side of the 
mid-line of the vulval orifice).  They are attached to each other by 
desmosomes with their interior apical faces making up the lumen of the 
vulva.  Cells B1 and B2 are fused in the adult into a single toroid (
designated B).  The ventral-most cell in the stack (A) is attached by 
desmosomes to the adjacent syncytial epidermal cell (hyp-7) and the 
dorsal-most cell (F) to the uv1 cells of the uterus.  The anterior and 
posterior regions of each toroidal cell contain the nuclei and are 
considerably thicker than the lateral regions.  The lateral regions of 
A, B, & C become particularly thin after vulva eversion and in some 
cases may part.
It seems likely that there are some local specializations between 
the vulval cells: E sends out lateral extensions and is attached to 
the seam cells on either side of the animal; the vm1 vulval muscles 
attach at the junction of C and D; D also seems to form a hinge point 
during vulval eversion, forming the rim to the vulval orifice in the 
adult.
The vm2 vulval muscles are attached distally to seam cells in the 
same region as the lateral attachment of the E vulva cell.  They are 
attached proximally to the junction of the F vulval cell and the uv1 
cells of the uterus.  The vm1 vulval muscles are attached distally to 
hyp-7, in a sub-ventral location between body muscle cells.  They are 
attached proximally to the junction of the C and D vulval cells.  The 
vulval muscles have well-defined myofilaments in the L4, but in 
contrast, the uterine muscles have a very different appearance at this 
stage with a very prominent ER and no obvious myofilaments.
[See Figure 1]

Figure 1