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Suzanne L. Mansour

Professor of Human Genetics and
Adjunct Professor of Neurobiology and Anatomy

Suzi Mansour

B.A. Harvard University

Ph.D. University of California, Berkeley

Research

References

suzi.mansour@genetics.utah.edu

Suzi Mansour's Lab Page

Suzi Mansour's PubMed Literature Search

Molecular Biology Program

FGFs and Inner Ear Development, Mouse models of hearing loss and restoration

Research

The inner ear, which mediates the sensations of hearing and balance, is derived almost entirely from a small patch of ectodermal cells that are specified for an otic fate early in fetal development. Through a series of tissue interactions that are mediated by secreted signaling molecules, otic cells undertake complex processes of morphogenesis and differentiation to achieve their final functional form. Abnormalities of these processes lead to congenital deafness, which is the most common human sensory disorder. To better understand these disorders, my laboratory employs genetic and molecular approaches to identify and characterize genes that are important for the development and/or function of the mouse inner ear.

Fibroblast growth factor (FGF) signaling plays critical roles in the early development of the ear. Disruption of either Fgf3 or Fgf10 leads to variable defects of mouse inner ear morphogenesis and our studies show that Fgf3 plays a critical role in sustaining dorsal otic gene expression. In addition, we found that Fgf3/Fgf10 double mutants have no ear development at all, showing that these genes are required redundantly for the initial induction of the otic placode, as well as individually in subsequent morphogenetic steps. Fgf3/Fgf8 double mutants have a similar phenotype because Fgf8 is upstream of Fgf10. We are using conditional mutants to dissect the tissue origins of these inductive FGF signals In addition, microarray comparisons of control and FGF-deficient otic placodes revealed transcriptional targets of FGF signaling (Urness et al., 2010). Several interesting candidates for roles in otic induction and subsequent inner ear development are under further investigation.

Ablation of Fgf3 and Fgf10 alleles specifically within the otic epithelium has revealed dosage sensitive roles for these genes in directing both cochlear and vestibular morphogenesis. Our results show that Fgf3 and Fgf10 have unappreciated roles in cochlear development. Together with the Schoenwolf laboratory we are investigating how these FGF signals are coordinated with BMP and SHH signals to regulate the cell behaviors driving otic morphogenesis.

Many forms of sensorineural hearing loss, whether caused by genetic or environmental factors, are characterized by loss of cochlear sensory cells, which do not regenerate in mammals. In contrast, birds and fish regenerate lost sensory cells from residual cochlear supporting cells. Strategies for hearing restoration in mammals are focused on manipulating developmental signals to change cochlear supporting cell identity. We showed that mice with an activating mutation in FGFR3 that models Muenke syndromehave hearing loss associated with an identity switch between two distinct types of supporting cells. We found that supporting cell identity and hearing are restored in these FGFR3 mutants by genetically reducing the level of FGF10, a ligand does not normally activate FGFR3. Accordingly, we found that the mutation changes FGFR3 specificity so that it becomes responsive to FGF10. Most remarkably, we found that the supporting cell fate switch is actually completed the “rescued” animals, but is then gradually reversed. This shows that seemingly fully differentiated cochlear supporting cells can reversibly switch fates in an FGF-dependent manner. Since some immature supporting cells can be induced under certain circumstances to convert to sensory cells, this FGF-dependent plasticity is being investigated so that it be exploited as a component of strategies designed to promote mammalian sensory cell regeneration from supporting cells.

Figure 1

Fig. 1. (A) An E15.5 mouse embryo was cleared and its inner ear filled with latex paint. (B) Section taken through an E18.5 mouse cochlear duct showing expression of Dusp6 (purple).
Cochlear duct section stained with antibodies directed against MYO7A (green) and CD44 (red) reveals sensory hair cells and supporting cells in the mouse inner ear.

References

  1. Ohta S, Wang B, Mansour SL and Schoenwolf GC (2016) BMP regulates regional gene expression in the dorsal otocyst through canonical and non-canonical intracellular pathways. Development 143: 2228-2237.

  2.  Ohta S, Wang B, Mansour SL and Schoenwolf GC (2016) SHH ventralizes the otocyst by maintaining basal PKA activity and regulating GLI3 signaling. Dev. Biol. 420:100-109.

  3.  Quadros RM^, Miura H^, Harms DW, Akatsuka H, Sato T, Aida T, Redder R, Richardson GP, Inagaki Y, Sakai D, Buckley SM, Seshacharyulu P, Batra SK, Behlke MA, Zeiner SA, Jacobi AM, Izu Y, Thoreson WB, Urness LD, Mansour SL* Ohtsuka M* and Gurumurthy CB* (2017) Easi-CRISPR: a robust method for one-step generation of mice carrying conditional and insertion alleles using long ssDNA donors and CRISPR ribonucleoproteins. Genome Biol. 18:92 ^=co-first authors, *=co-corresponding authors

  4. Urness LD, Wang X, Shibata S, Ohyama T and Mansour SL (2015) Fgf10 is required for specification of non-sensory regions of the cochlear epithelium. Dev Biol. 400:59-71
  5. Mansour SL, Li C and Urness LD (2013) Genetic rescue of Muenke syndrome model hearing loss reveals prolonged FGF-dependent plasticity in cochlear supporting cell fates. Genes Dev. 27:2320-2331
  6. Urness LD, Bleyl SB, Wright TJ, Moon AM and Mansour SL (2011) Redundant and dosage sensitive requirements for Fgf3 and Fgf10 in cardiovascular development. Dev. Biol. 356:383-397
  7. Ohta S, Mansour SL and Schoenwolf GC (2010) BMP/SMAD signaling regulates the cell behaviors that drive the initial dorsal-specific regional morphogenesis of the otocyst. Dev Biol. 247:369-381
  8. Urness LD, Paxton C, Wang X, Schoenwolf GC and Mansour SL (2010) FGF signaling regulates otic placode induction and refinement by controlling both ectodermal target genes and hindbrain Wnt8a. Dev. Biol. 340:595-604
  9. Mansour SL, Twigg, SRF, Freeland RM, Wall SA, Li C and Wilkie AOM (2009) Hearing loss in a mouse model of Muenke syndrome. Hum. Mol. Genet. 18:43-50
  10. Hatch EP, Urness LD and Mansour SL (2009) Fgf16IRESCre mice: A tool to inactivate genes expressed in inner ear cristae and spiral prominence epithelium. Dev. Dyn. 238:358-366
  11. Urness LD, Li C, Wang X and Mansour SL (2008) Expression of ERK signaling inhibitors Dusp6, Dusp7 and Dusp9 during mouse ear development. Dev. Dyn. 237:163-169
  12. Hatch E, Noyes CA, Wang X, Wright TJ and Mansour SL (2007) Fgf3 is required for dorsal patterning and morphogenesis of the inner ear epithelium. Development 134:3615-3625
  13. Li C, Scott DA, Hatch E, Tian X and Mansour SL (2007) Dusp6 (Mkp3) is a negative feedback regulator of FGF-stimulated ERK signaling during mouse development. Development 134:167-176
  14. Ladher RK, Wright TJ, Moon AM, Mansour SL and Schoenwolf GC (2005) FGF8 initiates inner ear induction. Genes Dev. 19:603-613
  15. Wright TJ and Mansour SL (2003) Fgf3 and Fgf10 are required for mouse otic placode induction. Development 130:3379-3390

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Last Updated: 8/8/17