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Initial assesment of PDE6b
This article is not listed in the Developmental Biology stub list. However, it has been largely involved in my research project, it's relevant to this course since its function and expression pattern during the development stage is crucial for understanding the molecular pathway in phtototransduction. Also, this article is a stub so it still has a lot more to improve. References: ,
 * 1) The article didn't clearly articulate the definition of the Pde6b
 * 2) lack of illustrative figures
 * 3) Poor arrangements of the information, partially because of the lack of the information

Preliminary outline of PDE6B
Summary of PDE6b (Brief instruction)

Structure of PDE6

Mutation of PDE6b （the involvement of disease and the pathway)

=Summary= PDE6b is the beta subunit of rod photoreceptor cGMP phosphodiesterase 6(PDE6) coded by PDE6b gene which is important in visual phototransduction. The existence of this beta subunit is essential for the PDE6 to function normally. Mutation of this subunit is responsible for various kinds of retinal degeneration such as Retinitis Pigmentosa.

=Structure= PDE6 is a protein complex located on the photoreceptor outer segment which plays an important role in phototransduction cascade. There are two types of photoreceptor: Cone and Rod. Cone PDE6 complex and rod PDE6B complex have different structures. PDE6b together with PDE6a and two identical inhibitory subunits PDE6r form rod PDE6b holoenzyme while cone PDE6b complex only consists of two identical PDE6a catalytic subunits. PDE6B--one of the catalytic units in rod PDE6, is composed of three domains.TWo N-terminal GAF domains and one C-terminal catalytic domain.The non-catalytic GAF domains are responsible for cGMP binding. The C-terminal interacts with membrane by isoprenylation and carboxylmethylation.

=Mutation= Mutation of PDE6b leads to the dysfunction of PDE, which results in failure of hydrolysis of cGMP. The rd1 mouse is an well-characterized animal model of retinitis pigmentosa caused by the mutation of PDE6b gene. There is a insertion of Murine leukemia provirus near the first exon combined with a point mutation which introduces a stop codon in exon 7. In addition to the rd1 mouse, a missense mutation (R560C) in exon 13 of the Pde6b gene, is the character of another animal model of recessive retinal degeneration.

rd1 mouse
This phenotype is characterized by the early onset retinal degeneration (starting at postnatal day 10) caused by PDE6b mutation. The phenotype was first discovered on rodless mice during World War II by Keeler. After that, studies have shown that other than loss of rod, there is severe impairment of outer segments and inner segments. Finally, the cone undergoes degeneration, which causes the mutants to completely go blind.