DNA replication licensing in somatic and germ cells.
The DNA replication (or origin) licensing system ensures precise duplication of the genome in each cell cycle and is a powerful regulator of cell proliferation in metazoa. Studies in yeast, Drosophila melanogaster and Xenopus laevis have characterised the molecular machinery that constitutes the licensing system, but it remains to be determined how this important evolutionary conserved pathway is regulated in Homo sapiens. We have investigated regulation of the origin licensing factors Cdc6, Cdt1, Mcm2 and Geminin in human somatic and germ cells. Cdc6 and Cdt1 play an essential role in DNA replication initiation by loading the Mcm2-7 complex, which is required for unwinding the DNA helix, onto chromosomal origins. Geminin is a repressor of origin licensing that blocks Mcm2-7 loading onto origins. Our studies demonstrate that Cdc6, Cdt1 and Mcm2 play a central role in coordinating growth during the proliferation-differentiation switch in somatic self-renewing systems and that Cdc6 expression is rate-limiting for acquisition of replication competence in primary oocytes. In striking contrast, we show that proliferation control during male gametogenesis is not linked to Cdc6 or Mcm2, but appears to be coordinated by the negative regulator Geminin with Cdt1 becoming rate-limiting in late prophase. Our data demonstrate a striking sexual dimorphism in the mechanisms repressing origin licensing and preventing untimely DNA synthesis during meiosis I, implicating a pivotal role for Geminin in maintaining integrity of the male germline genome.
Eward
Kathryn Leigh
KL
Wolfson Institute for Biomedical Research, University College London, The Cruciform Building, Gower Street, London, WC1E 6BT, UK.
Obermann
Ellen C
EC
Shreeram
S
S
Loddo
Marco
M
Fanshawe
Thomas
T
Williams
Craig
C
Jung
Hyo-Il
HI
Prevost
A Toby
AT
Blow
J Julian
JJ
Stoeber
Kai
K
Williams
Gareth H
GH
D017398:Alternative Splicing; D000818:Animals; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D003106:Colon / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004261:DNA Replication; D005260:Female; D005434:Flow Cytometry; D064248:Geminin; D018922:HL-60 Cells; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D019394:Ki-67 Antigen / Q000096:biosynthesis; D008297:Male; D008540:Meiosis; D064111:Minichromosome Maintenance Complex Component 2; D008938:Mitosis; D009687:Nuclear Proteins / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D011418:Prophase; D020133:Reverse Transcriptase Polymerase Chain Reaction; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D013091:Spermatogenesis; D013737:Testis / Q000378:metabolism; D013997:Time Factors; D029867:Xenopus Proteins
C066503:CDC6 protein, S cerevisiae; C467199:CDT1 protein, human; D018797:Cell Cycle Proteins; C577998:GMNN protein, Xenopus; C577995:GMNN protein, human; D064248:Geminin; D019394:Ki-67 Antigen; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins; D029867:Xenopus Proteins; D004247:DNA; C084859:MCM2 protein, human; D064111:Minichromosome Maintenance Complex Component 2