Mice homozygous for the mocha spontaneous mutation (Ap3d1mh) have increased perinatal mortality. They are recognizable at birth by the absence of visible pigment in the eyes, which darken to deep red in adults. The hairs have considerably smaller and fewer melanin granules than normal. Behavior is abnormal, characterized by hyperactivity, tilted heads, and in some the inability to swim. All homozygotes show degenerative changes in the organ of Corti, stria vascularis, and spiral ganglion, and most show abnormalities of the otoliths in the saccule and utricle. This degeneration can be lessened by the administration of supplemental manganese or, to a lesser degree, zinc to the dam during pregnancy. Evoked auditory brainstem responses appear normal in young homozygotes, but decrease with age coincident with the cochlear degeneration with no response detected after six months of age. At three months of age, mice homozygous for the Ap3d1mh allele have significantly increased auditory evoked potentials after the first of two paired tones. Ap3d1mh-2J homozygotes also show an increased response to thefirst tone but this has not been proven with statistical significance. Homozygotes also show prolonged bleeding times due to a platelet storage pool deficiency (SPD) associated with reduced granulation of the platelets. Consistent with this defective vesicle transport, homozygotes also have decreased levels of renal lysosomal enzymes in the urine. Mocha is thus a mouse mutation that, like pa (pallid) and mu (muted), offers a model for human Hermansky-Pudlak syndrome, combining pigment and otolith abnormalities with platelet SPD. Electrocorticograms from awake Ap3d1mh homozygotes show a constant, high voltage, bilaterally synchronous theta wave pattern that is diminished by chloral-hydrate anesthetization. Heterozygotes also have occasional brief bursts of lower voltage theta waves. Ap3d1mh-2J homozygotes do not display hypersynchronized electrocorticograms but have spike-wave and tonic clonic seizures. Ap3d1mh homozygotes may be fertile but are poor breeders. (Lane and Deol, 1974; Rolfson and Erway, 1984; Noebels and Sidman, 1989; Miller et al., 1999; Peden et al., 2002; Kantheti et al., 1998 and 2003.)
This strain is also segregating for the grizzled (gr) spontaneous mutation. gr is a recessive mutation that occasionally causes tail kinks and consistently causes dilution of the yellow pigment but not the black pigment of the hair. The coat color has been described as similar to chinchilla (Tyrc-ch/Tyrc-ch) but with the black pigment remaining undiluted. On the agouti JIGR/Dn background the gr/gr coat color is grayish agouti. On a non-agouti background the hair in the ears and around the genitalia is white. The gr mutation causes 40-50% mortality prior to phenotypic classification and this affects males more than females. This mortality is both postnatal and prenatal from approximately 10 days onward. Pregnant dams expected to carry some homozygotes have been found to carry some dead embryos some of which had craneofacial abnormalities including shortened snout and swollen optic and occipital regions. At birth homozygotes weigh an average of one quarter less than their wildtype siblings. Although they increase in weight as suckling pups, as adults they still weigh 5-25% less than their wildtype siblings. (Falconer, 1950; Bloom and Falconer, 1966.)
This strain is homozygous for the rd1 allele of Pde6b resulting in early onset retinal degeneration in all pups. (Lane and Deol, 1974; Qiao et al., 2003.)
