Biology Reference
In-Depth Information
diversity in the patterns of cell division within nematode embryos. Studies of vulval
cell lineages in several species have been critical to our understanding of evolution of
developmental mechanisms. As transgenic tools are now being developed in other
nematode species, their use in automated analysis is likely to increase; the embry-
onic cell lineage of C. briggsae has already been followed using automated histone-
GFP lineage tracing (
Zhao et al., 2008
).
III. Resources
The descriptions of cell lineages from the late 1970s remain the definitive
descriptions of the cellular anatomy (
Table II
). In learning the anatomy an important
initial goal is to compare one
'
s own drawings with the diagrams in the following
papers. In particular, the description by
Sulston et al. (1983)
remains the best
resource for learning embryonic anatomy; an ''embryo'' section of WormAtlas is
currently under construction.
WormAtlas (
www.wormatlas.org
)andtheC. elegans Atlas book (
Hall and Altun,
2008
) are invaluable for understanding adult anatomy and for correlating cellular
anatomy with electron micrographs. The web site contains a small section on cell
identification. A good online guide to cell identification is in Wormbook (
Yochem,
2006
), with plentiful Nomarski DIC images of ''landmark'' cells. This is an important
addition to the original lineage papers. However, in our experience the only way to
successfully learn cell identification is to sit at the microscope and draw what one sees.
IV. Nomenclature and Conventions
The nomenclature for cells was set out by
Sulston and Horvitz (1977)
and
systematized by
Sulston et al. (1983)
. Every cell in C. elegans can be named
according to its ancestry, for example, ABpla. Terminally differentiated cells also
have ''functional'' names that are either semiarbitrary (e.g., ASEL) or descriptive of
terminal fate (hyp 7). For example, the cell ABalppppppaa is the neuron ASEL.
Embryonic cells are named beginning with one of the five early embryonic
''founder cells'': AB, E, MS, C, D. The cells P
0
through P
4
denote the zygote and
the precursors of the germ line, and should not be confused with the postembryonic
blast cells P1-P12. Cells that go on to divide in postembryonic stages are renamed
with a blast cell name (e.g., ABplapapaaa=QL), and their progeny named according
to similar rules.
The suffixes in lineage names refer to the approximate orientation of the cell
division relative to the overall axes of the embryo or larva: anterior/posterior, dorsal/
ventral, left/right. Almost all cell divisions in C. elegans have a clear anterior-
posterior orientation; indeed only
8 embryonic cell divisions are predominantly
in the transverse (left-right) axis. Cells are named according to the relative position
of the daughters at the time of division, even if the daughters subsequently change
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