XXII. BIOCHEMICKÝ ZJAZD - Jesseniova lekárska fakulta

Lectures
OSTERIX OVER-EXPRESSION IN HUMAN EMBRYONIC STEM CELLS AND
ITS EffECT ON CELL DIffERENCIATION
Radim Černý 1 , Elerin Kärner 2 , Christian Unger 3 and Mikael Wendel 2
1
Department of Biochemistry, LFUK Plzeň, 2 Center for Oral Biology and 3 Department
of Medicine, Karolinska Institutet, Stockholm, Sweden
Osterix (Osx) is a recently identified zinc finger-containing transcription factor encoded
by the Sp7 gene, which regulates gene expression in committed osteoblastic precursor
cells, acting downstream of Runx2 (Nakashima et al.: Cell 108, 143, 2002). We have overexpressed
Osx after lentiviral transfer of Osx cDNA recombined with enhanced green
fluorescent protein (EGFP) into the genome of human embryonic stem cells (HESC) line
H9. We obtained two HESC subpopulations expressing two significantly different levels
of Osx. Both subpopulations exhibited spontaneous differentiation and reduced expression
of markers characteristic of the pluripotent phenotype, such as SSEA3, Tra I-60, and
Nanog. The high level of Osx expression, compared to endogenous levels found in primary
human osteoblasts, did not enhance osteogenic differentiation, and did not up-regulate
collagen I expression. Instead, the high Osx levels induced the commitment towards
the hematopoietic-endothelial lineage by up-regulating the expression of CD34 and
Gata I. However, low levels of Osx expression up-regulated collagen I, bone sialoprotein
and osteocalcin production. Conversely, forced high level expression of the homeobox
transcription factor HoxB4, a known regulator for early hematopoiesis, promoted osteogenesis
in HESCs, while low levels of HoxB4 lead to hematopoietic gene expression. We
conclude that for an enhanced osteogenesis originating from in vitro cultured HESCs,
the correct levels of ectopic transcription factors need to be established. Our data also
highlight the notion of close relationship between early blood and bone development.
52 XXII. Biochemistry Congress, Martin