Homozygotes are fully viable and fertile.Eyes develop normally up to 7 to 10 days after birth. At this stage the outer segment of the rod cell has begun to form, and in wild type mice it elongates rapidly during the 10th to 15th days. In Pde6b^rd1/Pde6b^rd1 mice the nascent outer segments and the rod cells degenerate rapidly so that by 15 days there is only a thin layer of rod cells left, and they have disappeared completely by 35 days (J:5250, J:5708). The inner nuclear layer and the retinal ganglion cells appear normal butmay show slight quantitative reduction (J:5812, J:5292).

Although the eyes of Pde6b^rd1 homozygotes are devoid of normal rods, the mice have some visual capacity (J:5980). About 3% of cones among the visual cells degenerate at a much slower rate than do rods, so that a few cones are still present at 18 months (J:5988). The surviving cones are postulated (J:25157) as the light receptors required for the persistence of circadian responses to dawn and dusk in Pde6b^rd1 homozygotes past the sstage when rods have disappeared (J:29236).

In fusion chimeras between wild type and Pde6b^rd1 homozygous embryos, the Pde6b^rd1 mutant acts in the photoreceptor cells rather than in the pigment epithelium of the retina (J:5708). Action within photoreceptor cells is also implied by the long term survival of wild type rod cells transplanted into Pde6b^rd1 homozygote retinas (J:20769). At a stage before degeneration can be seen, a deficiency of cGMP-PDE, andan excess of cGMP, appears in rod photoreceptor cells (J:5332).

The rate of retinal degeneration in mutants doubly homozygous for two retinal degeneration mutations (Pde6b^rd1 and Rds^Rd2) is intermediate between those of the two homozygotes (J:12044). The double homozygote shows an intermediate level of mRNAs for the ß subunit of cGMP-PDE and for several other phototransduction related proteins, suggesting an interaction between Pde6b^rd1 and Rds^Rd2 (J:2579).

Genbank ID for mutant sequence: M75166

The flexed-tail mutation appeared in a stock maintained by Dr. H.R. Hunt at Michigan State College (J:12951). Homozygotes are small at birth and have a transitory hypochromic, microcytic anemia characterized by a large number of siderocytes containing non-heme iron granules. Most homozygotes also have flexed tail and a belly spot, but these arenot constant manifestations of the mutant. Because of the anemia there is probably greater postnatal mortality among f/f than among normal mice (J:14979).

The anemia begins on the 12th day of embryonic life when the liver first starts to produce blood cells (J:14979). It is most intense at 15 days of gestation and still severe at birth, but by 2 weeks of age has disappeared. Although adults have normal blood values, their response to hemopoietic stress is defective (J:5439, J:27511).

The results of numerous studies have led to the conclusion that the prenatal deficiency in number of erythrocytes and the defective response of adult erythropoietic cells are due to a delay in maturation of already committed erythroid stem cells, and that earlieruncommitted precursors are unaffected by f (J:5439, J:5654, J:5582).

An additional effect of f in homozygotes is defective heme synthesis, which occurs in fetal reticulocytes but not in adult reticulocytes nor in erythroblasts at earlier stages of maturation. In fetal reticulocytes there is normal uptake of iron but poor incorporation into hemoglobin (J:5439), probably as a result of reduced activity of delta-aminolevulinate synthetase and dehydratase (J:5591).

Fetal erythrocytes of f/f mice have more alpha than beta globin chains. In both f/f and wild type fetal erythrocytes there is more alpha- than beta-chain mRNA; probably some regulatory mechanism bringing about equal alpha- and beta-chain synthesis exists in wild type mice but is defective in f/f (J:5827, J:30711).

The tail abnormalities are first noticeable on the 14th day of gestation as abnormal differentiation of the intervertebral discs (J:13090). The possibility that abnormal heme synthesis could cause the tail and pigment defects in f/f mice has been discussed (J:5591).

It was suggested that flexed-tail might be a mutation in the mouse homolog Fancc of the gene defective in human Fanconi anemia, complementation group C, but no mutation in the Fancc gene or abnormalitiesin Fancc mRNA have been detected in f/f mutants (J:13598). Also, flexed-tail mice are not susceptible to increases in chromosomal aberrations induced by mitomycin C, a characteristic of Fancc mutant mice (J:35839).

Allele arose on a genetically undefined stock in 1927 and was subsequently transferred onto several genetic backgrounds to create the congenic and recombinant inbred lines Je/Le-f/f, FL1/ReJ, WB/ReJ-f/f and C57BL/6J-f/f. The phenotypes listed above might be associated with any of thesestrains; in most cases it was not specified.

Cryorecovery to establish a Dedicated Supply for greater quantities of mice.
One to two pairs will be recovered to establish a Dedicated Supply of mice. Price by quotation. For more information on Dedicated Supply, please contact JAX^® Services: Tel: 1-800-422-6423 or 1-207-288-5845; Email: jaxservices@jax.org.
Genomic DNA is available for this strain from the Mouse DNA Resource.