All Phenotypes Pax8<tm1Pgr> MGI Mouse

lethality at weaning, complete penetrance ( J:129545 )

• homozygotes die around weaning time due to athyroidism

• early T4-substitution (initiated at P2) restores postnatal development and extends survival to adulthood

premature death ( J:47310 )

• homozygotes are born at the expected Mendelian frequency but die shortly after weaning due to a thyroid defect

• application of thyroxine extends survival up to 6 months

postnatal lethality, complete penetrance ( J:116236 )

• most homozygotes die within the first weeks after birth and none survive weaning

• daily injections of T4 (20 ng/g/body weight) extend survival to old age with no overt deficits, even if initiated as late as P14

• however, complete recovery is not restored by immediate postnatal T4 substitution, indicating that some deficits result from prenatal T4 deficiency of the offspring

abnormal outer ear morphology ( J:116236 )

• 22 of 43 athyroid homozygotes show outer ear abnormalities ranging from small pinnae to completely absent pinnae

• notably, outer-ear abnormalities are confined to minor size reductions of the pinnae and ear canals in adult T4-substituted homozygotes

abnormal external auditory canal morphology ( J:116236 )

• 22 of 43 homozygotes show outer ear abnormalities ranging from narrow ear canals to completely closed ear canals

external auditory canal stenosis ( J:116236 )

absent outer ear ( J:116236 )

small ears ( J:116236 )

postnatal growth retardation ( J:47310 , J:116236 )

• homozygotes exhibit growth retardation after one week of birth (J:47310)

• homozygotes display variable but obvious postnatal growth retardation relative to wild-type mice (J:116236)

abnormal adenohypophysis morphology ( J:117324 )

• athyroid male homozygotes display a highly abnormal cellular composition of the anterior pituitary

• early T4-substitution (initiated at P2) restores pituitary hormone mRNA expression and anterior pituitary cellular composition to wild-type values at postpubertal age (>45 days)

decreased lactotroph cell number ( J:117324 )

• almost complete absence of lactotropes

decreased somatotroph cell number ( J:117324 )

• a severely reduced number of somatotropes

increased thyrotroph cell number ( J:117324 )

• hypertrophy and hyperplasia of the thyrotropes

abnormal thyroid gland morphology ( J:47310 )

• at E17 and at birth, mutant thyroids are composed almost completely of calcitonin-producing C-cells

absent thyroid follicular cells ( J:47310 )

• no thyroxine-producing follicular cells are detected

abnormal thyroid gland development ( J:47310 )

• at E11.5, the mutant thyroid diverticulum fails to expand laterally as in wild-type mice, and instead resembles that of E10.5 embryos

• at E12.5, follicular-cell precursors are not formed, as the collar-shaped structure is completely absent

• at E15.5, the only remaining thyroid structure is the ultimobranchial body

abnormal thyroid diverticulum morphology ( J:47310 )

• at E11.5, the mutant thyroid diverticulum fails to expand laterally as in wild-type mice, and instead resembles that of E10.5 embryos

small thyroid gland ( J:47310 )

• homozygotes display a small thyroid gland

• in contrast, no structural defects are observed in the developing kidney or spinal cord

decreased testis weight ( J:117324 )

• postpubertal T4-substituted male homozygotes (age >45 days) display a significantly reduced testis weight, not observed in prepubertal T4-substituted males (age 23-29 days)

testicular atrophy ( J:117324 )

decreased circulating thyroxine level ( J:47310 , J:116236 )

• at 2 weeks of age, homozygotes display significantly reduced serum thyroxine levels relative to wild-type mice (J:47310)

• homozygotes lack detectable serum T4 levels at all postnatal test ages (J:116236)

decreased circulating triiodothyronine level ( J:116236 )

• homozygotes lack detectable serum T3 levels at all postnatal test ages

abnormal kinocilium morphology ( J:116236 )

• at P20-P21, athyroid homozygotes occasionally exhibit rudimentary kinocilia

abnormal outer ear morphology ( J:116236 )

• 22 of 43 athyroid homozygotes show outer ear abnormalities ranging from small pinnae to completely absent pinnae

• notably, outer-ear abnormalities are confined to minor size reductions of the pinnae and ear canals in adult T4-substituted homozygotes

abnormal external auditory canal morphology ( J:116236 )

• 22 of 43 homozygotes show outer ear abnormalities ranging from narrow ear canals to completely closed ear canals

external auditory canal stenosis ( J:116236 )

absent outer ear ( J:116236 )

small ears ( J:116236 )

abnormal auditory bulla morphology ( J:116236 )

• 20 of 31 athyroid homozygotes display abnormal middle ears with poorly calcified cartilaginous bulla, sometimes filled with a jelly-like substance

delayed inner ear development ( J:116236 )

• all athyroid homozygotes exhibit a ~7-day delay in inner ear development relative to wild-type mice

• at P12, the organ of Corti is still immature, Kolliker's organ is still present, the pillar cells have not elongated, and the tunnel of Corti remains closed

• at P16, the organ of Corti has developed, the pillars have elongated and the tunnel of Corti, as well as the inner sulcus have opened; however, the minor tectorial structures and marginal pillar cells are still present

• by P21, the tunnel of Corti and inner sulcus have enlarged, the spaces of Nuel around OHCs have formed but the tectorial membrane is still abnormally thick

• at P13, the mutant inner ear is still in the stage of Kolliker's organ without a tunnel of Corti

abnormal organ of Corti morphology ( J:119450 )

• at 2 weeks after birth, athyroid homozygotes display an immature organ of Corti at the light microscopy level

• in contrast, early TH-substituted homozygotes exhibit a mature organ of Corti at P15

abnormal cochlear hair cell morphology ( J:116236 )

• at P20-P21, athyroid homozygotes exhibit immature IHCs and OHCs over the entire apical surface, with numerous microvilli

abnormal cochlear hair cell stereociliary bundle morphology ( J:116236 )

• at P20-P21, athyroid homozygotes exhibit numerous, enlarged stereocilia over the apical surface of immature IHCs and OHCs

• at this ages, mutant supporting cells also display significantly more stereocilia on their apical surface than normal

• late T4-substituted homozygotes (P8 or later) exhibit disarray of stereovilli from both inner and outer cochlear hair cells

• the extent of structural disorder increases the later T4 substitution is initiated

abnormal outer hair cell stereociliary bundle morphology ( J:116236 )

• at P21, the apical ends of mutant OHC stereocilia are still covered by a contiguous membrane (""granular layer""), which is normally completely absent in wild-type mice at P20

abnormal cochlear IHC efferent innervation pattern ( J:119450 )

• at P15, athyroid homozygotes exhibit prolonged efferent innervation of IHCs by olivocochlear fibers, in contrast to the developmental decline of efferent IHC innervation noted in wild-type mice

abnormal inner hair cell synaptic ribbon morphology ( J:119450 )

• at P14-P15, athyroid IHCs display an immature afferent synaptic organization, with higher numbers of ribbons and immature synaptic contacts (showing several ribbons) relative to mature wild-type IHCs where fewer and confined single ribbon synapses are observed

• early TH-substitution restores normal maturation of ribbon synapse morphology and function in IHCs of P14-P15 athyroid homozygotes

cochlear outer hair cell degeneration ( J:116236 )

• late T4-substituted homozygotes (P8 or later) exhibit OHC loss, predominantly in the basal part of the cochlea

abnormal pillar cell morphology ( J:116236 )

• at P21, homozygotes display abnormal persistence of marginal pillar cells, normally lost at P20 in wild-type mice

enlarged tectorial membrane ( J:116236 )

• at >P12, the mutant tectorial membrane is permanently thicker than normal with cavities in the center; minor tectorial structures persist through at least P16

• at P13, mutant tectorial membranes show an apical to basal decrease in thickness that is less evident in wild-type mice

• the tectorial membrane remains abnormally thick even when T4 substitution is initiated at P8 or later

abnormal middle ear morphology ( J:116236 )

• 20 of 31 athyroid homozygotes display abnormal middle ears with poorly calcified cartilaginous bulla, sometimes filled with a jelly-like substance

• notably, middle-ear abnormalities persist in 51 of 77 ears from T4-substituted homozygotes

abnormal stapedial artery morphology ( J:116236 )

• 20 of 31 homozygotes display a malformed or absent stapedial artery

absent stapedial artery ( J:116236 )

• 20 of 31 homozygotes display a malformed or absent stapedial artery

absent round window ( J:116236 )

• in 20 of 31 homozygotes, the round window of the cochlea is often smaller or completely absent

decreased round window size ( J:116236 )

• in 20 of 31 homozygotes, the round window of the cochlea is often smaller or completely absent

abnormal middle ear ossicle morphology ( J:116236 )

• 20 of 31 homozygotes display malformations of the middle-ear ossicles

• mutant middle-ear ossicles are always calcified, never cartilaginous

abnormal stapes morphology ( J:116236 )

• 20 of 31 homozygotes show a malformed stapes with an abnormal articulation to the oval window

• the mutant stapes is occasionally immobile, fixed in the oval window

abnormal stapes crus morpholgy ( J:116236 )

• one of the crurae of the stapes is regularly missing or much thinner than normal

abnormal cochlear inner hair cell physiology ( J:119449 , J:119450 )

• in contrast to wild-type IHCs which stop spontaneous spiking activity (i.e. generation of Ca²⁺ action potentials, APs) at P8, athyroid IHCs generate Ca²⁺ APs as late as at P14 (i.e. beyond the onset of hearing); however, no differences in amplitude and frequency of spontaneous Ca²⁺ APs are noted until P7 (J:119449)

• injection of small positive currents prolongs the period of spiking until P12 in wild-type IHCs and until P21 in athyroid IHCs, indicating persistence of induced spiking activity (J:119449)

• in athyroid IHCs, persistence of Ca²⁺ APs until P21 is due to (i) failure of downregulation of the Ca²⁺ current (I_Ca) at P13-P18, and (ii) failure of upregulation of the large-conductance Ca²⁺-activated K⁺ (BK) current due to lack of expression of I_K,f (fast-activating potassium current carried by BK channels) at P12 or later (J:119449)

• specifically, Ca²⁺ currents are elevated 3-fold after P12 while the K⁺ current of athyroid IHCs is only ~43% that of wild-type IHCs at P16, with no differences in peak K⁺ currents noted at early neonatal stages (P2-P4) (J:119449)

• athyroid IHCs perform exocytosis until P21; however, exocytosis efficiency is significantly reduced in the third postnatal week (59% of wild-type), typical for immature, prehearing IHCs (J:119449)

• surprisingly, otoferlin protein (a key component in IHC exocytosis) is present in athyroid mouse IHCs at P12, but not expressed in IHCs of hypothyroid rats at P9 or P18 (J:119449)

• athyroid homozygotes display impaired maturation of presynaptic function in cochlear IHCs (J:119450)

• Ca²⁺ currents of athyroid IHCs are smaller than wild-type currents at P6-P8 but ~2.5-fold larger than those of wild-type IHCs at 2 weeks after birth, indicating delayed Ca²⁺ current upregulation and lack of downregulation up to P15 (J:119450)

• voltage dependence of Ca²⁺ current in athyroid IHCs is normal at P14-P16 but displays a slightly more hyperpolarized peak potential in athyroid IHCs at P6-P8 relative to wild-type IHCs (J:119450)

• early TH-substitution (initiated at birth) restores the Ca²⁺ current amplitudes of athyroid IHCs to wild-type values at P15 (J:119450)

• the efficiency of Ca²⁺ influx in triggering fast exocytosis of the readily releasable vesicle pool is reduced in athyroid IHCs at P14-P16 relative to mature wild-type IHCs (J:119450)

• notably, the efficiency of sustained exocytosis in P14-P16 athyroid IHCs exceeds that of immature wild-type IHCs (J:119450)

• despite substantial Ca²⁺ currents, little exocytosis is observed in athyroid IHCs at P6-P8 for all but very long stimulus durations (J:119450)

• early TH-substitution (initiated at birth) restores normal Ca²⁺ currents and exocytic capacitance changes of athyroid IHCs at P15, consistent with a partial restoration of hearing after TH substitution (J:119450)

• at P14-P16, athyroid IHCs lack large-conductance Ca²⁺-activated K⁺ currents and KCNQ4 currents, with abnormal persistence of Ca²⁺ action potentials (J:119450)

• P14-P16 athyroid IHCs display more depolarized resting potentials and immature passive electrical properties relative to wild-type IHCs (J:119450)

increased or absent threshold for auditory brainstem response ( J:116236 )

• even when T4 substitution is started at P1, ABR thresholds, measured at 6 weeks of age or more, are elevated by ~20 dB, and each day of delay in the start of T4 substitution results in an additional threshold loss of ~4 dB

deafness ( J:116236 )

• at P21, athyroid homozygotes exhibit no auditory brain stem responses (ABR) to sound at 130 dB SPL

• adult hearing can be nearly normalized by early postnatal substitution with thyroxine (T4); however, structural and functional restoration of hearing is incomplete