Worm Breeder's Gazette 15(4): 45 (October 1, 1998)

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.

Chromosome Segregation: A Role for APC Genes in C. elegans

D Chase1, L Wille2, D Ferris1, A Golden1, D Shakes2

1 Developmental and Signal Transduction Group, NCI-FCRDC
2 Dept of Biology, College of William and Mary, Williamsburg, VA

        The Anaphase Promoting Complex (APC) is an E3 ubiquitin ligase
which  functions at various points in the cell cycle to target  specific
proteins  for proteasome proteolysis (1).  The APC is responsible for
the metaphase-anaphase transition as well as exit from mitosis.  Yeast
mutants of APC genes arrest with  unsegregated 2N chromosome content and
a short spindle (2).  
        Our lab has long been interested the genes emb27 and emb30 which
we now know affect both mitotic and meiotic divisions in the germline
(3).  We have decided to study APC in C. elegans since germline APC
knockouts would be predicted to have mitotic defects similar to emb27
and emb30.   Little is known about whether APC functions during either
oocyte or sperm meiosis (particularly meiosis I), but we are very
interested in this question.  
        To study the Anaphase Promoting Complex in  C. elegans, we are
systematically knocking out individual APC proteins using RNAi and
looking for meiotic and mitotic defects.   We want to study not only
various components of the APC, but also upstream regulators and
downstream targets of the APC.  Using the C. elegans Blast server, we
have identified worm homologous of yeast APC genes cdc27, cdc16, cdc23,
apc1, apc2 and apc5.  We have also identified esp1, an indirect
substrate of the APC and mad1, a component of the cell cycle checkpoint
which  regulates the activity of APC.
        Preliminary results from RNAi injections of apc 1 and apc2
suggest that the APC does in fact function during meiosis.  RNAi of 
apc1 results in fertilized oocytes which arrest in meiosis I and never
form polar bodies.  The DNA of the fertilized oocyte arrests with its
maternal chromatin in the  anterior part of the oocyte, while the sperm
DNA stays posterior and tightly condensed.  RNAi gonadal knockouts of
apc2 result in  a weaker, metaphase delay phenotype; embryos within
injected mothers are largely in meiotic or mitotic metaphase. 
Apparently M-phase is prolonged, however, the cells eventually divide.
        Our results to date indicate that C. elegans APC homologues are
required for both oocyte meiosis and embryogenic mitosis.  We intend to
further characterize the effect of APC RNAi not only on oocyte meiotic
but also on sperm meiotic and germline mitotic divisions. 

1.  Cohen-Fix and Koshland (1997) Metaphase to Anaphase transition:
Avoiding a Mid-life Crisis.  Current Opinion in Cell Biology, 9:800-806.
2.  Hartwell and Smith (1985) Altered fidelity in mitotic chromosome
transmission in cell cycle mutants of Saccharomyces cerevisiae. 
Genetics, 110:381-395.
3.  Sadler et al, this issue.