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Fig. 1. Mutants in dilute lethal have severely disrupted electroretinographic responses. (A) Waveforms of electroretinograms from a dilute mouse (Myo5a^d/Myo5a^d) on the left and a dilute lethal mutant (Myo5a^d-l/Myo5a^d-l) on the right, at the maximum light intensity. The a-wave is the first negative (downward) deflection and the b-wave is the later positive deflection, with oscillatory potentials caused by retinal interneuron activity superimposed. The dilute lethal waveforms show reduced amplitudes of response and an anomalous shape caused by disproportionate reduction of the b-wave. Scale bar for both waveforms shown on left. (B) Response amplitudes ± standard error plotted as a funct ion of light intensity: (left) a-waves; (right) b-waves. There is a significant difference between dilute and dilute lethal amplitudes for a-waves from 4.2 log units of attenuation (4.2-3.6, P<0.01; 3.3-0, P<0.001) and from 7.2 log units of attenuation for the b-waves (7.2-4.8, P<0.005; 4.2-0, P<0.001; see inset). At maximum flash intensity, a-wave amplitudes are reduced by 38% and b-wave amplitudes by 51% in Myo5a^d-l/Myo5a^d-l (n=12) compared with Myo5a^d/Myo5a^{d or d-l} (n=12; includes six Myo5a^d/Myo5a^d and six Myo5a^d/Myo5^d-l; there was no significant difference between these two genotypes for any electroretinographic parameter analysed, P>0.25 for all). All mice were between postnatal days 19 and 25 (both groups averaged 21 days of age), ages when the Myo5a^d-l/Myo5a^d-l are clearly afflicted with the neurological phenotype. (C) Light microscopy of retinas from a Myo5a^d/Myo5a^d dilute control (left) and a Myo5a^d-l/Myo5a^d-l dilute lethal mutant (right), at 20 days of age. No obvious differences were seen in outer segment length or any other feature of gross structure. Scale bar, 10 µm.

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