This would most closely approximate the situation in human heterozygous individuals with P216L-based dominantly inherited retinitis pigmentosa. The photoreceptor outer segment phenotype reflected this range of expression. Figure 1 illustrates This point for the outer segments of animals at 6-7 months of age. Surprisingly, the central feature of the phenotype was shortening of the outer segments rather than major disorganization of the discs. Outer segment discs were normally aligned except for the occasional absence or separation of the lamellar portions of cohorts of discs within the outer segment stack.
Outer segments appear normal in terms of their order and length.
Levels of transgenic mRNA expression also correlated inversely with photoreceptor cell survival. This phenotype is the result of haploinsufficiency or semidominance of the gene. In terms of total outer segment volume in younger heterozygotes one to two months of age, this represents about half of the volume occupied by wild type outer segments. A. Non-transgenic retina showing characteristic oversized, curled outer segment discs. The outer segments are more dysmorphic than their nontransgenic counterparts.