Dilute

The melanophilin gene (MLPH) has some recessive alleles which cause a diluted version of the original coat colour.

Working mechanism

The protein that is encoded by the MLPH gene plays an important role in the distribution of pigment particles in the cell. It binds the melanosomes (pigment particles) to the actin skeleton in the cell. This skeleton makes sure that the pigment is distributed throughout the cell. The mutations disrupt this and the colour looks diluted. Melanocytes are stretched out through the tissue. If the pigment is concentrated in a single location then it looks like a small dot. On a larger scale this looks like a diluted colour.

Variants

The first mutation that was discovered, termed d¹ is a change in a single nucleotide. It makes it very likely that translation to mRNA is cut off very early, resulting in a very short and non-functional peptide. Homozygous dd dogs have only about 25% of functional MLPH compared to homozygous DD dogs.

A second variant (d²)is a mutation of a single nucleotide but more to the end of the protein. Nevertheless it disrupts the function of the protein in such a way that the phenotype is the same as with d¹d¹ dogs.

The most recent discovery is the d³ variant which is caused by an insertion of a nucleotide. This also causes an early stop to the DNA sequence and thus the MLPH protein is approximately half the original size.

Alleles

D : normal colour (wild type)
d¹ : dilute
d² : dilute
d³ : dilute