Program of the 2001 International Worm Meeting - Sternberg Lab ...

981
similar to the tim-1 (RNAi) phenotype. We
narrowed down the candidates to csg-5 (t1545)
(chromosome segregation defective), isolated by
Gonczy et al. in a maternal-effect embryonic
lethal screen for genes involved in cell division
(4). We sequenced t1545 and found a single
base transition, resulting in a Gly924Asp
mutation in a region moderately conserved
among timeless proteins. A long-range PCR
product containing the tim-1 coding region plus
3.3 kb 5’- and 1.3 kb 3’-flanking sequence fully
rescued the embryonic lethality of t1545. These
results indicate that tim-1 is csg-5.
Recently, the identification of a second
Drosophila timeless gene (dTIM2) was reported
(2,3). dTIM2 is more closely related to TIM-1
and the single mammalian TIM protein than it is
to dTIM. Interestingly, timeless knock-out mice
die during early embryogenesis around a period
of rapid cell proliferation (3), suggesting that
mouse TIM and TIM-1 may play similar roles in
the cell cycle and have functions distinct from
the functions of the Drosophila clock protein
dTIM.
1. Sehgal A, Price JL, Man B, Young MW.
Science. (1994) 263:1603-6.
2. Benna C, Scannapieco P, Piccin A,
Sandrelli F, Zordan M, Rosato E, Kyriacou
CP, Valle G, Costa R. Curr Biol. (2000)
10:512-3.
3. Gotter AL, Manganaro T, Weaver DR,
Kolakowski LF Jr, Possidente B, Sriram S,
MacLaughlin DT, Reppert SM. Nat
Neurosci. (2000) 3:755-6.
4. Gonczy P, Schnabel H, Kaletta T,
Amores AD, Hyman T, Schnabel R. J Cell
Biol. (1999) 144:927-46.
982. The C.elegans CIP/KIP-type
cyclin-dependent kinase inhibitor
CKI-1 is cell-autonomously required
for postmitotic differentiation as well
as cell cycle arrest.
Masamitsu Fukuyama, Joel H.
Rothman
Department of MCD Biology, University of
California, Santa Barbara, CA 93106
982
Although it has been long observed that some
processes of differentiation, such as changes in
cell shape and cell migration, are generally
incompatible with cell division during animal
development, the cellular biochemistry
underlying such phenomena is still unknown.
In previous worm meetings, we showed that the
cki-1 gene is required to arrest the cell cycle
during C. elegans embryogenesis. CKI-1
belongs to the conserved CIP/KIP
cyclin-dependent kinase inhibitor (CKI) family.
Studies in other systems have demonstrated that
overexpression of CIP/KIP CKIs leads to G1
arrest by inhibiting the activity of various
cyclin/CDK complexes, which positively
regulate the cell cycle.
We also reported previously that expression of
various postmitotic differentiation markers is
diminished in cki-1(RNAi) embryos and adults,
as seen in mice defective for CIP/KIP CKI
function. These findings suggest that CIP/KIP
CKIs might directly promote postmitotic
differentiation as well as cell cycle arrest.
Alternatively, hyperplasia caused by loss of
CIP/KIP CKIs activity may disturb intercellular
signaling processes required for normal
differentiation. Although the former hypothesis
is supported by in vitro studies showing that
overexpression of CIP/KIP CKIs induce
terminal differentiation in some mammalian cell
cultures, this has not been experimentally
demonstrated in vivo.
We have found that elimination of cki-1
function by RNAi can prevent expression of two
postmitotic embryonic gut markers, pho-1::GFP
and Ce-npa-1::GFP (gifts from T. Fukushige, J.
McGhee, and I. Johnstone), concomitant with
gut hyperplasia. As we have also found that
isolated E cells express Ce-npa-1::GFP, these
results strongly suggest that cki-1 is