Early requirement for fgf8 function during hindbrain pattern formation in zebrafish

Abstract

Fibroblast growth factor (FGF) signaling is required for normal development of the vertebrate brain, including the isthmus and caudal regions of the hindbrain. Recent work in zebrafish has identified a requirement for the combination of fgf3 and fgf8 functions in specification of rhombomeres 5 and 6 (r5, r6), when evaluated at mid-and late somitogenesis stages. However, when examined earlier in development, during early somitogenesis stages, FGF8 alone is required to initiate r5 and r6 development. Both a mutation in fgf8 and injection of fgf8-targeted antisense morpholino-modified oligonucleotides result in suppression of genes normally expressed in r5 and r6 by the one-to two-somite stage. This expression recovers by the six-somite stage, and we propose that this recovery is a response to activation of fgf3 and to delayed accumulation of fgf8. These data demonstrate an early, nonredundant requirement for fgf8 function in hindbrain patterning.

Hindbrain patterning requires fine-tuning of early krox20 transcription by Sprouty 4

“…Previous studies have shown that FGF signalling plays an essential role in the control of Krox20 expression in r3 and r5 (Aragon and Pujades, 2009;Marin and Charnay, 2000;Maves et al, 2002;Walshe et al, 2002;Wiellette and Sive, 2003;Wiellette and Sive, 2004). Here we investigated the timing, the level of action and the mechanisms of FGF control.…”

“…The transcription factor MafB, which is encoded in zebrafish by mafba, is necessary for Krox20 expression in r5 (Cordes and Barsh, 1994;Moens et al, 1996;Wiellette and Sive, 2003). MafB expression requires FGF signalling (Aragon and Pujades, 2009;Maves et al, 2002;Walshe et al, 2002;Wiellette and Sive, 2003;Wiellette and Sive, 2004). We investigated the dynamics of mafba expression and found that Spry4 loss-offunction led to the premature onset of mafba in r5/r6: at 95% epiboly, all Spry4 morphants expressed mafba (n28), versus only 12% of control embryos (n33; c 2 -test, P<0.0001; see Fig.…”

“…Among them, Fibroblast growth factor (FGF) signalling is necessary in particular to promote Krox20-mediated r3 and r5 development (Aragon and Pujades, 2009;Marin and Charnay, 2000;Maves et al, 2002;Walshe et al, 2002;Wiellette and Sive, 2003;Wiellette and Sive, 2004). It has been shown in zebrafish and chick embryos that Krox20 expression requires prior FGF signalling (Aragon and Pujades, 2009;Walshe et al, 2002).…”

Expression and functions of FGF ligands during early otic development

“…Using both approaches, a reduction in size of the otic vesicle combined with reduced or loss of expression of otic markers has been observed (Phillips et al, 2001;Leger and Brand, 2002;Maroon et al, 2002;Liu et al, 2003). The size of the otic vesicle in Fgf8 morphants appears slightly smaller than in Fgf3 morphants, possibly due to a non-redundant requirement for FGF8 during hindbrain patterning influencing otic induction (Wiellette and Sive, 2004). The central role of the hindbrain during inner ear induction is also underlined by the fact that only wild-type hindbrain cells rescue Pax2 expression in Fgf8 mutant embryos in cell transplantation experiments (Leger and Brand, 2002).…”

“…Foxi1 has therefore been termed a competence factor for FGF3 and FGF8 that permits the acquirement of otic fate by preplacodal cells, as assessed by Pax8 expression (Nissen et al, 2003;Hans et al, 2004;Solomon et al, 2004;Hans et al, 2007). On the other hand, Pax8 morphants have more profound defects during inner ear induction in a Fgf8 mutant background than in the presence of Fgf3 morpholinos, indicating once again a more dominant role for FGF8 compared to FGF3 (Wiellette and Sive, 2004;Mackereth et al, 2005). A second pair of competence factors for FGF signalling, Dlx3b and Dlx4b, have been shown to be required for the proper initiation of Pax2a expression at a later stage (Hans et al, 2004;Mackereth et al, 2005).…”