Mediator complex subunit Med12 regulates cardiac jelly development and AV valve formation in zebrafish

Segert, J., Schneider, I., Berger, I.M., Rottbauer, W., Just, S.
Progress in Biophysics and Molecular Biology   138: 20-31 (Journal)
Registered Authors
Berger, Ina, Just, Steffen, Rottbauer, Wolfgang, Schneider, Isabelle, Segert, Julia
Cardiac jelly, Has2, Heart valve development, Med12, Tbx2b, Zebrafish
MeSH Terms
  • Animals
  • Endocardium/metabolism
  • Gene Expression Regulation, Developmental
  • Heart/growth & development*
  • Heart Valves/growth & development*
  • Hyaluronan Synthases/metabolism
  • Mediator Complex/deficiency
  • Mediator Complex/genetics
  • Mediator Complex/metabolism*
  • Mutation
  • Zebrafish/growth & development*
  • Zebrafish/metabolism*
  • Zebrafish Proteins/deficiency
  • Zebrafish Proteins/genetics
  • Zebrafish Proteins/metabolism*
30036562 Full text @ Prog. Biophys. Mol. Biol.
The molecular mechanism essential for the formation of heart valves involves complex interactions of signaling molecules and transcription factors. The Mediator Complex (MC) functions as multi-subunit machinery to orchestrate gene transcription, especially for tissue-specific fine-tuning of transcriptional processes during development, also in the heart. Here, we analyzed the role of the MC subunit Med12 during atrioventricular canal (AVC) development and endocardial cushion formation, using the Med12-deficient zebrafish mutant trapped (tpd). Whereas primary heart formation was only slightly affected in tpd, we identified defects in AVC development and cardiac jelly formation. We found that although misexpression of bmp4 and versican in tpd hearts can be restored by overexpression of a modified version of the Sox9b transcription factor (harboring VP16 transactivation domain) that functions independent of its co-activator Med12, endocardial cushion development in tpd was not reconstituted. Interestingly, expression of tbx2b and its target hyaluronan synthase 2 (has2) - the synthase of hyaluronan (HA) in the heart - was absent in both uninjected and Sox9b-VP16 overexpressing tpd hearts. HA is a major ECM component of the cardiac jelly and required for endocardial cushion formation. Furthermore, we found secreted phosphoprotein 1 (spp1), an endocardial marker of activated AV endocardial cells, completely absent in tpd hearts, suggesting that crucial steps of the transformation of AV endocardial cells into endocardial cushions is blocked. We demonstrate that Med12 controls cardiac jelly formation Sox9-independently by regulating tbx2b and has2 expression and therefore the production of the glycosaminoglycan HA at the AVC to guarantee proper endocardial cushion development.
Genes / Markers
Show all Figures
Mutations / Transgenics
Human Disease / Model
Sequence Targeting Reagents
Engineered Foreign Genes