Severe piebaldism and profound hearing loss in mutant pigs
derived from ENU mutagenesis
During N-ethyl-N-nitrosourea (ENU) mutagenesis, we designed a
three-generation breeding scheme to retrieve dominant and recessive
mutations in the F1 offspring(Hai, Cao, et al., 2017). A dominant
mutation was identified in a male pig (G1-016105) with pigmentation
abnormalities. The G1-016105 was mated with a wild-type Bama sow,
resulting in 63 offspring from 10 litters (Fig. 1a). Among them, 27
offspring had the “two-ends” black color, and 36 showed severe
piebaldism similar to G1-016105, including 16 males and 20 females (Fig.
1b). The mutant piglets showed symmetrical pigmentation abnormalities
with white hair and skin on the forehead, cheek, the entire ear, and the
distal part of the tail, which is highly similar to the distribution of
piebaldism in humans (Fig. 1c). Moreover, the iris color of mutant pigs
was normal. The blood cell analysis of peripheral blood did not find any
marked difference in the mutant pigs (Table. S1).
As the hypopigmentation in the skin is primarily associated with hearing
loss in human Waardenburg syndrome (WS)(Saleem, 2019), we conducted an
auditory brainstem response (ABR) test in the mutant and wild-type
littermates at postnatal day 7. Mutant pigs did not produce any
recognizable waveforms up to 100 dB sound pressure level (SPL) stimuli
in the range of 1–32 kHz, whereas wild-type pigs produced ABR
thresholds at 10–30 dB SPL (Fig. 1d, 1e). The ABR test on every
offspring showed a linkage between piebaldism and hearing loss. The
frequency of the two phenotypes was compared with expected Mendelian
ratios using a χ2 test
(χc2=1.0159<χ0.05(1)2), suggesting that the mutant
phenotype is inherited in an autosomal dominant pattern (Table 1).