PUBLICATION

Fgf-dependent otic induction requires competence provided by Foxi1 and Dlx3b

Authors

Hans, S., Christison, J., Liu, D., and Westerfield, M.

ID

ZDB-PUB-070210-20

Date

2007

Source

BMC Developmental Biology 7(1): 5 (Journal)

Registered Authors

Christison, Joe, Hans, Stefan, Liu, Dong, Westerfield, Monte

Keywords

none

MeSH Terms

Animals
Signal Transduction
Ear, Inner/embryology*
Fibroblast Growth Factors/genetics*
Choristoma/embryology
Embryo, Nonmammalian
In Situ Hybridization
Zebrafish/embryology*
Zebrafish/genetics
Homeodomain Proteins/genetics*
Zebrafish Proteins/genetics*
Gastrula
RNA, Messenger/biosynthesis
Gene Expression Regulation, Developmental*
Forkhead Transcription Factors/genetics*
Microinjections
Animals, Genetically Modified
Fibroblast Growth Factor 3/genetics*

(all 18)

PubMed

17239227 Full text @ BMC Dev. Biol.

Abstract

BACKGROUND: The inner ear arises from a specialized set of cells, the otic placode, that forms at the lateral edge of the neural plate adjacent to the hindbrain. Previous studies indicated that fibroblast growth factors (Fgfs) are required for otic induction; in zebrafish, loss of both Fgf3 and Fgf8 results in total ablation of otic tissue. Furthermore, gain-of-function studies suggested that Fgf signaling is not only necessary but also sufficient for otic induction, although the amount of induced ectopic otic tissue reported after misexpression of fgf3 or fgf8 varies among different studies. We previously suggested that Foxi1 and Dlx3b may provide competence to form the ear because loss of both foxi1 and dlx3b results in ablation of all otic tissue even in the presence of a fully functional Fgf signaling pathway. RESULTS: Using a transgenic line that allows us to misexpress fgf8 under the control of the zebrafish temperature-inducible hsp70 promoter, we readdressed the role of Fgf signaling and otic competence during placode induction. We find that misexpression of fgf8 fails to induce formation of ectopic otic vesicles outside of the endogenous ear field and has different consequences depending upon the developmental stage. Overexpression of fgf8 from 1-cell to midgastrula stages leads to formation of no or small otic vesicles, respectively. Overexpression of fgf8 at these stages never leads to ectopic expression of foxi1 or dlx3b, contrary to previous studies that indicated that foxi1 is activated by Fgf signaling. Consistent with our results we find that pharmacological inhibition of Fgf signaling has no effect on foxi1 or dlx3b expression, but instead, Bmp signaling activates foxi1, directly and dlx3b, indirectly. In contrast to early activation of fgf8, fgf8 overexpression at the end of gastrulation, when otic induction begins, leads to much larger otic vesicles. We further show that application of a low dose of retinoic acid that does not perturb patterning of the anterior neural plate leads to expansion of foxi1 and to a massive Fgf-dependent otic induction. CONCLUSION: These results provide further support for the hypothesis that Foxi1 and Dlx3b provide competence for cells to respond to Fgf and form an otic placode.

Genes / Markers

Figures

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Expression

Gene	Fish	Conditions	Stage	Qualifier	Anatomy	Assay	Figure
cldna	bmp7a^ty68a/ty68a	heat shock	10-13 somites		otic placode	ISH	Fig. 6
cldna	WT	standard conditions	10-13 somites		otic placode	ISH	Fig. 6
dlx3b	bmp7a^ty68a/ty68a	heat shock	Bud		ectoderm	ISH	Fig. 3
dlx3b	WT	chemical treatment: pharmaceutical	Bud	Not Detected	ectoderm	ISH	Fig. 4
dlx3b	WT	chemical treatment: SU5402	Bud		ectoderm	ISH	Fig. 2
dlx3b	WT	standard conditions	Bud		ectoderm	ISH	Fig. 2
dlx3b	WT	standard conditions	Bud		ectoderm	ISH	Fig. 4
dlx3b	WT	standard conditions	Bud		ectoderm	ISH	Fig. 3
dlx3b	WT + MO1-vent + MO1-vox	standard conditions	Bud		ectoderm	ISH	Fig. 3
etv4	bmp7a^ty68a/ty68a	heat shock	1-4 somites		whole organism	ISH	Fig. 5

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Phenotype

Fish	Conditions	Stage	Phenotype	Figure
WT + MO1-dlx3b	standard conditions	Prim-5	otic vesicle decreased size, abnormal	Fig. 7
WT + MO1-dlx3b + MO2-foxi1	standard conditions	Prim-5	otic vesicle aplastic, abnormal	Fig. 7
WT + MO2-foxi1	standard conditions	Prim-5	otic vesicle decreased size, abnormal	Fig. 7
b1193Tg (AB)	heat shock	Prim-5	otic vesicle increased size, abnormal	Fig. 6
b1193Tg (AB)	heat shock	Prim-5	otic vesicle increased size, abnormal	Fig. S3
b1193Tg (AB)	heat shock	Long-pec to Protruding-mouth	otic vesicle size, normal	Fig. S3
b1193Tg + MO1-dlx3b (AB)	heat shock	Prim-5	otic vesicle decreased size, abnormal	Fig. 7
b1193Tg + MO1-dlx3b + MO2-foxi1 (AB)	heat shock	Prim-5	otic vesicle aplastic, abnormal	Fig. 7
b1193Tg + MO2-foxi1 (AB)	heat shock	Prim-5	otic vesicle decreased size, abnormal	Fig. 7

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Mutations / Transgenics

Allele	Construct	Type	Affected Genomic Region
b1193Tg	Tg(hsp70l:fgf8a)	Transgenic Insertion
em1		Indel	foxi1
t24149		Point Mutation	fgf3
ti282a		Point Mutation	fgf8a
ty68a		Point Mutation	bmp7a

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Human Disease / Model

Sequence Targeting Reagents

Target	Reagent	Reagent Type
dlx3b	MO1-dlx3b	MRPHLNO
foxi1	MO2-foxi1	MRPHLNO
vent	MO1-vent	MRPHLNO
vox	MO1-vox	MRPHLNO

Fish

Fish
b1193Tg (AB)
b1193Tg + MO1-dlx3b (AB)
b1193Tg + MO1-dlx3b + MO2-foxi1 (AB)
b1193Tg + MO2-foxi1 (AB)
bmp7a^ty68a/ty68a
fgf3^{t24149/t24149}
fgf3^{t24149/t24149}; fgf8a^{ti282a/ti282a}
fgf8a^{ti282a/ti282a}
foxi1^em1/em1
WT

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Antibodies

Orthology

Engineered Foreign Genes

Mapping

Hans et al., 2007 ZDB-PUB-070210-20 PMID:17239227

Fgf-dependent otic induction requires competence provided by Foxi1 and Dlx3b

Hans et al., 2007

ZDB-PUB-070210-20
PMID:17239227