International Mammalian Genome Society

The 14th International Mouse Genome Conference (2000)

B6. PYK2b, a Candidate Gene for Rupture of Lens Cataract in Mice

Hiroshi Hiai1, Yun Wang1, Shinya Toyokuni1, Masayoshi Tachibana2, Yoshibumi Matsushima2
1Dept. of Pathology and Biology of Diseases, Kyoto Univ. Graduate School of Medicine and
Saitama Cancer Center Research Institute

Rupture of lens cataract (RLC) was a hereditary recessive cataract in mice, featuring rupture of lens at about 35 days of age due to degeneration of cortical lens fiber at posterior suture and lens-capsule junction. We mapped the responsible gene at 28 cM on chromosome 14 (Genomics, 1996). Linkage analysis of 404 (RLC x MSM)F1 x RLC mice pin-pointed a chromosomal segment containing rlc locus. The P1 clone covering this segment contained protein tyrosine kinase 2b (PYK2b), detected as 705 bp sequence in the PCR with a primer set in the kinase domain of PYK2b gene.

On the other hand, we prepared an BALB/c isoantiserum to RLC lens extract. In western blot, RLC lens showed a unique 40 kDa peptide not seen in BALB/c or STS mice. Western blot of RLC, BALB/c and STS lens with anti-PYK2b C-terminus peptide antibody showed that these strains shared a 116 kDa full size PYK2b peptide, but RLC lens had a unique additional 40 kDa band. The 40 kDa peptide seen by anti-RLC isoantiserum is same as the PYK2b C-terminus peptide, since the immunoprecipitate by anti-RLC lens revealed the 40 kDa specific band when immunoblotted with anti-PYK2b C-terminus peptide. These observation suggest that RLC lens produces an excessive C-terminus peptide of PYK2b.

PYK2b, also called related adhesion focal tyrosine kinase RAFTK or CAKb, is a protein kinase frequently associated with focal adhesion kinase involved in intracellular signaling in cell adhesion. PYK2b has two splicing variants, one of which is PRNK, a C-terminus peptide lacking kinase domain with MW 40 kDa. Lens fibers form basement membrane complex (BMC) at their junctions in posterior suture or attachment sites to capsule. PYK2b was shown to colocalize with BMC and heavy deposit of its C-terminus peptide was seen exclusively in RLC lens. These observation suggest that PYK2b is a component of BMC and abnormal deposit of its splicing product may cause the rupture of lens at the posterior pole in RLC mice.

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