Fibroblast growth factor 4 and its novel splice isoform have opposing effects on the maintenance of human embryonic stem cell self-renewal.
Human embryonic stem cells (HESCs) are unique in their capacity to self-renew while remaining pluripotent. This undifferentiated state must be actively maintained by secreted factors. To identify autocrine factors that may support HESC growth, we have taken a global genetic approach. Microarray analysis identified fibroblast growth factor 4 (FGF4) as a prime candidate for autocrine signaling. Furthermore, the addition of recombinant FGF4 to HESCs supports their proliferation. We show that FGF4 is produced by multiple undifferentiated HESC lines, along with a novel fibroblast growth factor 4 splice isoform (FGF4si) that codes for the amino-terminal half of FGF4. Strikingly, although FGF4 supports the undifferentiated growth of HESCs, FGF4si effectively counters its effect. Furthermore, we show that FGF4si is an antagonist of FGF4, shutting down FGF4-induced Erk1/2 phosphorylation. Expression analysis shows that both isoforms are expressed in HESCs and early differentiated cells. However, whereas FGF4 ceases to be expressed in mature differentiated cells, FGF4si continues to be expressed after cell differentiation. Targeted knockdown of FGF4 using small interfering RNA increased differentiation of HESCs, demonstrating the importance of endogenous FGF4 signaling in maintaining their pluripotency. Taken together, these results suggest a growth-promoting role for FGF4 in HESCs and a putative feedback inhibition mechanism by a novel FGF4 splice isoform that may serve to promote differentiation at later stages of development.
Mayshar
Yoav
Y
Department of Genetics, The Life Sciences Institute, The Hebrew University, Jerusalem 91904, Israel.
Rom
Eran
E
Chumakov
Irina
I
Kronman
Achia
A
Yayon
Avner
A
Benvenisty
Nissim
N
D017398:Alternative Splicing / Q000235:genetics*; D000818:Animals; D019898:Autocrine Communication / Q000187:drug effects; D002452:Cell Count; D002454:Cell Differentiation / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D053595:Embryonic Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D051519:Fibroblast Growth Factor 4 / Q000235:genetics* / Q000494:pharmacology; D006801:Humans; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D039904:Pluripotent Stem Cells / Q000166:cytology / Q000187:drug effects; D020033:Protein Isoforms / Q000235:genetics / Q000494:pharmacology
D051519:Fibroblast Growth Factor 4; D020033:Protein Isoforms; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3