Changes in cyclin dependent kinase expression and activity accompanying lens fiber cell differentiation.
Previous studies from this laboratory have shown that differentiating lens fiber cells contain two active cyclin dependent kinases (Cdks), Cdk1 and Cdk5. The present study was undertaken to explore the expression and regulation of six additional members of the Cdk family (Cdk2, Cdk3, Cdk4, Cdk6, Cdk7 and Cdk8) during lens differentiation. Differentiating lens fiber cells were separated from lens epithelial cells by microdissection of developing rat lenses [embryonic day 16 (E16) to postnatal day 8 (P8)] and Cdk expression was assessed by RT-PCR and immunoblotting. Two Cdks (Cdk3 and Cdk6) were not expressed in lens fiber cells or epithelial cells during this developmental period. In the lens epithelium, we detected proteins and mRNAs corresponding to all other Cdks examined (Cdk2, Cdk4, Cdk7, Cdk8) throughout this developmental period. Epithelial cells showed significant Cdk2 activity, which decreased with developmental age, but no significant activity was detected for Cdk4, Cdk7, or Cdk8. Fiber cells contained all four Cdk proteins and the corresponding Cdk mRNAs except for Cdk2 mRNA. None of the Cdks examined showed significant kinase activity in fiber cells. Immunoprecipitates of Cdk2 and Cdk4 from fiber cells contained p57(kip2), supporting the view that this Cdk inhibitor blocks the activity of these Cdks in lens fibers. In contrast, p57(kip2)did not co-immunoprecipitate with Cdk5 from lens fibers. These findings suggest that the differential affinity of p57(kip2)for members of the Cdk family may provide a mechanism for specific regulation of individual Cdks during fiber cell differentiation.
Gao
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CY
Laboratory of Molecular and Developmental Biology, NEI/NIH, Bethesda, MD, 20892-2730, USA.
Rampalli
A M
AM
Cai
H C
HC
He
H Y
HY
Zelenka
P S
PS
D000818:Animals; D042846:CDC2-CDC28 Kinases; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases / Q000235:genetics* / Q000378:metabolism; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D004627:Embryonic Induction; D004847:Epithelial Cells / Q000378:metabolism; D015870:Gene Expression; D015151:Immunoblotting; D007908:Lens, Crystalline / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000095043:Cyclin-Dependent Kinase-Activating Kinase
D017931:DNA Primers; D011518:Proto-Oncogene Proteins; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495892:Cdk2 protein, rat; C495903:Cdk4 protein, rat; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; D000095043:Cyclin-Dependent Kinase-Activating Kinase