Seam cells lie along the apical midline of the hypodermis, at the extreme left and right sides between nose and tail (See SeamFIG1, FIG2 and FIG3. Note that in SeamFIG2 GFP marker is actually excluded from the seam cells).
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During postembryonic development, they can act as stem cells to produce neurons of lumbar ganglia (PLN, PVW and PVN), tail spike neurons ( PHC) and phasmidial support cells (Phso1, Phso2), and sensory bristles along the sides (PDE, PDEsh and PDEso from V5 lineage; ADEso from H2 lineage) and in the male tail (anterior male rays). The seam cells are responsible for production of the cuticular alae in L1 stage, dauer larvae, and adults (See SeamFIG4 and SeamFIG5). There is no alae production in L2, L3 and L4.
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Interestingly, individual seam cells that yield sensory bristles do not form alae, so that the alae are interrupted over the length of one seam cell at the rays and at supernumerary bristles in some mutants (Maloof et al, 1999; Zhao and Emmons, 1995).
Each seam cell varies greatly in cross-section along its length, in order to accomodate the cell body, but is smoothly tapered in shape overall. Thus, at the cell body the seam may completely interrupt lateral hypodermis, while at its peripheral points, the seam is so thin that the lateral hypodermis runs behind it, enfolding it completely (See HypFIG6). The seam cells are linked to the hypodermis by very small adherens junctions (aj) along the full length at their apical borders, and by small gap junctions on their lateral membranes.
The apical face of each seam cell faces the cuticle and remains in contact with the cuticle along the full length of the cell. The seam is usually in exact register with the alae in the cuticle.
(For embryonic development
of the seam cells see Embryonic
development of the hypodermis)
At hatching, there are two rows of 10 seam cells on each side of the animal
which are embedded in hyp7 and are in close contact with the ventral epithelial
(P) cells (See
HypFIG5). About 5 hrs after hatching, and at the beginning of each larval
stage the seam cells H1, H2, V1-6 and T undergo cell division whereas the most
anterior cell, H0, does not divide. As a general rule the posterior daughter
of each seam cell division becomes a seam cell while the anterior daughters
become detached in their apical surfaces and fuse to hyp 7 syncytium. (Hedgecock
and White, 1985; Podbilewicz
and White, 1994; Shemer
and Podbilewicz, 2000). At the same time, each newly born seam cell
elongates and reaches its neighbor on both sides to make another row. This pattern
of division, hyp 7 fusion, and cell elongation repeats itself in each of the
larval stages until mid-L4. As a result of these divisions, a total of 98 syncytial
hypodermal nuclei and 30 new seam cells are generated. At mid-L4, 15 newly born
seam cells in each row elongate longitudinally and fuse with each other and H0 to form two continuous
lateral syncytia of seam cells (with 16 nuclei each) mostly embedded in the hyp 7 syncytium (See SeamFIG1).
This fusion event represents the last of the postembryonic somatic cell fusions
in C. elegans (
Podbilewicz and White, 1994)
1. Left side seam cells
Adult (L side ) seam cells (these cells fuse at L4 to make one row of
syncytium):
H1L.aa
H1L.appp
H2L.pppp
V1L.pappp
V1L.ppppp
V2L.pappp
V2L.ppppp
V3L.pappp
V3L.ppppp
V4L.pappp
V4L.ppppp
V5L.ppppp
(terminally differentiated as seam only in hermaphrodite; blast cell in male)
V6L.pappp
(terminally differentiated as seam only in hermaphrodite; blast cell in male)
V6L.ppppp
(terminally differentiated as seam only in hermaphrodite; blast cell in male)
TL.appa
(terminally differentiated as seam only in hermaphrodite; blast cell in male)
Additional (L side) seam cells in adult male:
V5L.pppapp
fuses with the main seam syncytium
V5L.pppppp
set cells (male tail seam; does not fuse with main seam and does not make alae)
V6L.papapp
set cells (male tail seam; does not fuse with main seam and does not make alae)
V6L.papppp
set cells (male tail seam; does not fuse with main seam and does not make alae)
V6L.pppapp
set cells (male tail seam; does not fuse with main seam and does not make alae)
V6L.pppppp
set cells (male tail seam; does not fuse with main seam and does not make alae)
Embryonic (L side) seam cells (do not form a syncytium):
H0L
H1L
(postembryonic blast cell)
H2L
(postembryonic blast cell)
V1L
(postembryonic blast cell)
V2L
(postembryonic blast cell)
V3L
(postembryonic blast cell)
V4L
(postembryonic blast cell)
V5L
(postembryonic blast cell)
V6L
(postembryonic blast cell)
TL
(postembryonic blast cell; functions as phasmid socket in L1)
2. Right side seam cells
Adult (R side ) seam cells (these cells fuse at L4 to make one row of
syncytium):
H1R.aa
H1R.appp
H2R.pppp
V1R.pappp
V1R.ppppp
V2R.pappp
V2R.ppppp
V3R.pappp
V3R.ppppp
V4R.pappp
V4R.ppppp
V5R.ppppp
(terminally differentiated as seam only in hermaphrodite; blast cell in male)
V6R.pappp
(terminally differentiated as seam only in hermaphrodite; blast cell in male)
V6R.ppppp
(terminally differentiated as seam only in hermaphrodite; blast cell in male)
TR.appa
(terminally differentiated as seam only in hermaphrodite; blast cell in male)
Additional (R side) seam cells in adult male:
V5R.pppapp
fuses with the main seam syncytium
V5R.pppppp
set cells (male tail seam; does not fuse with main seam and does not make alae)
V6R.papapp
set cells (male tail seam; does not fuse with main seam and does not make alae)
V6R.papppp
set cells (male tail seam; does not fuse with main seam and does not make alae)
V6R.pppapp
set cells (male tail seam; does not fuse with main seam and does not make alae)
V6R.pppppp
set cells (male tail seam; does not fuse with main seam and does not make alae)
Embryonic (R side) seam cells (do not form a syncytium):
H0R
H1R
(postembryonic blast cell)
H2R
(postembryonic blast cell)
V1R
(postembryonic blast cell)
V2R
(postembryonic blast cell)
V3R
(postembryonic blast cell)
V4R
(postembryonic blast cell)
V5R
(postembryonic blast cell)
V6R
(postembryonic blast cell)
TR
(postembryonic blast cell; functions as phasmid socket in L1)
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