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Gene Review

egr2  -  early growth response 2 (Krox-20 homolog)

Xenopus laevis

Synonyms: Krox-20, XKr20, XKrox-20, egr2-A, krox20
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High impact information on egr2-A

  • In these, four position-specific neural markers (engrailed-2, Krox-20, XlHbox 1, and XlHbox 6) were expressed in the ectoderm in the same A-P order as in the embryo [1].
  • Mauthner cell multiplications in the posterior hindbrain, and (both anteriorly and posteriorly) expanded Krox-20 expression domains indicated (partial) transformation of a large part of the hindbrain into (at least partial) rhombomere 3, 4 and/or 5 identity [2].
  • The response of later gastrula (stage 11-12) ectoderm to bFGF changes so that Krox 20 and En-2 are induced by bFGF alone, while induction of more posterior tissue marked by Hox B9 is eliminated [3].
  • In contrast to t-R4, platelet derived growth factor (PDGF)-dependent FGFR-1 activation in neuralized ectodermal cells expressing a chimeric PDGFR-FGFR-1 receptor results in the expression of Krox20 and Hoxb9 [4].
  • Krox-20, originally identified as a member of "immediate-early" genes, plays a crucial role in the formation of two specific segments in the hindbrain during early development of the vertebrate nervous system [5].

Biological context of egr2-A


Anatomical context of egr2-A

  • Krox-20 has been implicated in the segmental patterning of the hindbrain in the mouse by its expression prior to segment formation in alternating domains, which later correspond to r3 and r5 [6].
  • We speculate that this may reflect a distinct route of neural crest migration due to anatomical differences between these systems, rather than a difference in the site of origin of Krox-20-expressing crest [6].

Other interactions of egr2-A

  • Expression in embryos of a dominant interfering form of xGCNF reduces the expression of endogenous En-2 and Krox-20 [7].

Analytical, diagnostic and therapeutic context of egr2-A


  1. Planar induction of anteroposterior pattern in the developing central nervous system of Xenopus laevis. Doniach, T., Phillips, C.R., Gerhart, J.C. Science (1992) [Pubmed]
  2. Inhibition of retinoic acid receptor-mediated signalling alters positional identity in the developing hindbrain. van der Wees, J., Schilthuis, J.G., Koster, C.H., Diesveld-Schipper, H., Folkers, G.E., van der Saag, P.T., Dawson, M.I., Shudo, K., van der Burg, B., Durston, A.J. Development (1998) [Pubmed]
  3. Fibroblast growth factor is a direct neural inducer, which combined with noggin generates anterior-posterior neural pattern. Lamb, T.M., Harland, R.M. Development (1995) [Pubmed]
  4. Signaling specificities of fibroblast growth factor receptors in early Xenopus embryo. Umbhauer, M., Penzo-Méndez, A., Clavilier, L., Boucaut, J., Riou, J. J. Cell. Sci. (2000) [Pubmed]
  5. Functional role of a novel ternary complex comprising SRF and CREB in expression of Krox-20 in early embryos of Xenopus laevis. Watanabe, T., Hongo, I., Kidokoro, Y., Okamoto, H. Dev. Biol. (2005) [Pubmed]
  6. The structure and expression of the Xenopus Krox-20 gene: conserved and divergent patterns of expression in rhombomeres and neural crest. Bradley, L.C., Snape, A., Bhatt, S., Wilkinson, D.G. Mech. Dev. (1993) [Pubmed]
  7. A role for xGCNF in midbrain-hindbrain patterning in Xenopus laevis. Song, K., Takemaru, K.I., Moon, R.T. Dev. Biol. (1999) [Pubmed]
  8. Ventral ectoderm of Xenopus forms neural tissue, including hindbrain, in response to activin. Bolce, M.E., Hemmati-Brivanlou, A., Kushner, P.D., Harland, R.M. Development (1992) [Pubmed]
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