Expression of ERK signaling inhibitors Dusp6, Dusp7, and Dusp9 during mouse ear development

Abstract

The levels of fibroblast growth factor (FGF) signaling play important roles in coordinating development of the mouse inner, middle, and outer ears. Extracellular signal-regulated kinases (ERKs) are among the effectors that transduce the FGF signal to the nucleus and other cellular compartments. Attenuation of ERK activity by dephosphorylation is necessary to modulate the magnitude and duration of the FGF signal. Recently, we showed that inactivation of the ERK phosphatase, dual specificity phosphatase 6 (DUSP6), causes partially penetrant postnatal lethality, hearing loss and skeletal malformations. To determine whether other Dusps may function redundantly with Dusp6 during otic development, we surveyed the expression domains of the three ERK-specific DUSP transcripts, Dusp6, Dusp7, and Dusp9, in the embryonic mouse ear. We show that each is expressed in partially overlapping patterns that correspond to regions of active FGF signaling, suggesting combinatorial roles in negative regulation of this pathway during ear development.

Figure 1. Expression of Dusp6, Dusp7 and Dusp9 transcripts in the otic region of mid-gestation (E9-E11.5) embryos

(A-D₁) Dusp6 expression, (E-G) Dusp7 expression and (H-K₁) Dusp9 expression in whole embryos and sections (indicated by a subscript on the panel letter). Lines through whole embryos indicate the approximate plane of section of the corresponding section. All sections except H₁ and H₂ are in the transverse plane with dorsal up. Sections shown in H₁ and H₂ are oriented in the coronal plane with anterior (A) and posterior (P) indicated. Embryo stage is indicated in the lower right of each whole mount panel. The otic vesicle has been indicated with dashed white circles in panels E, F and G because it is difficult to see due to widespread Dusp7 staining. The blue precipitate inside the ov in C₁ is caused by non-specific filling with probe of the acellular space inside the vesicle during the whole mount hybridization. Abbreviations: 1, branchial arch 1; 2, branchial arch 2, ba1, branchial arch1; ba2, branchial arch 2; bc1, branchial cleft 1, oc, otic cup; om, otic mesenchyme, ov, otic vesicle.

Figure 2. Expression of Dusp6, Dusp7 and Dusp9 transcripts in the otic region of late gestation (E12.5-E18.5) embryos

(A₁-C₄) Transverse sections of left ears hybridized with Dusp6 probe. The approximate planes of section are denoted by white lines through age-matched paint-filled inner ears (A, E12.5; B, E14.5; C, E16.5). Dorsal and lateral orientations for all panels are as indicated in A₁. (D,D₁,E) Sagittal sections of E18.5 heads hybridized with Dusp6 probe. The caret in D denotes expression at the margin of the tympanic recess. D₁ shows a higher magnification view of the organ of Corti (oC), indicated by the boxed region in D, Panel E shows a representative section through the sensory region (crista) at the base of a semicircular canal. An arrow indicates the expression at the margin of the crista. (F,F₁,G,G₁) Dusp7 expression at E14.5 and E18.5. F₁ and G₁ show enlargements of the boxed regions in panels F and G, respectively. A caret indicates the margin of the cochlear duct. (H,H₁,I,I₁) Dusp9 expression at E14.5 and E16.5. H₁ and I₁ show enlargements of the boxed regions in panels H and I, respectively. Dusp6 (J), Dusp7 (K), and Dusp9 (L) expression in transverse sections of the E14.5 outer ear. Abbreviations: cd, cochlear duct; ep, cochlear epithelium; mes, mesenchyme; ed, endolymphatic duct; cc, common crus; usc, utriculosaccular chamber; g, spiral ganglion; psc, posterior semicircular canal; aa, anterior semicircular canal ampulla; la, lateral semicircular canal ampulla; oC, organ of Corti; ihc, inner hair cell; pc, pillar cells; ohc, outer hair cells; hc/cl, Hensen cells/Claudius cells; mal, malleus; mm, manubrium of the malleus; tm, tympanic membrane; om, otic mesenchyme; pin, pinna; eam, external acoustic meatus.