Cip/Kip cyclin-dependent protein kinase inhibitors and the road to polyploidy

Cell Division

Table 1 Polyploidy and expression of p57 and p21 in mice

Tissue	p57	p21	Polyploid	Mechanism
Placenta[18]	+	+	+	Endoreduplication
trophoblast stem cell→giant cell
Bone Marrow[4]	-	+	+	Endomitosis
megakaryoblast→megakaryocyte
Liver[3]	+	+	+	Acytokinetic Mitosis
hepatocyte development
Skeletal Muscle[13]	+	+	+	Cell Fusion
myoblast→myotube
Bone[15]	?	+	+	Cell Fusion
monocytes→osteoclasts
Placenta[8, 14]	?	+	+	Cell Fusion
Syncytiotrophoblasts
Heart Muscle[5, 6, 19]	+	+	+*	?
cardiomyocytes→myotube
Skin[9]	+	+	+*	?
basal epithelial cell→keratinocyte
Kidney[10]	+	-	+*	?
primitive podocyte→mature podo
Eye[7, 11]	+	?	?
lens epithelial cell→fiber cell
Bone[12]	+	+	?
osteoblast→bone
Cartilage[16, 17]	+	?	?
Chondrocytes→fiber cell

→ Indicates expression of p57 and p21 up-regulated during normal cell differentiation.
* Polyploidy results from injury (e.g. heart attack) or infection.

ISSN: 1747-1028