Mapping of the human CP49 gene and identification of an intragenic polymorphic marker to allow genetic linkage analysis in autosomal dominant congenital cataract

Long-lived metabolic enzymes in the crystalline lens identified by pulse-labeling of mice and mass spectrometry

The lenticular fiber cells are comprised of extremely long-lived proteins while still maintaining an active biochemical state. Dysregulation of these activities has been implicated in diseases such as age-related cataracts. However, the lenticular protein dynamics underlying health and disease is unclear. We sought to measure the global protein turnover rates in the eye using nitrogen-15 labeling of mice and mass spectrometry. We measured the ¹⁴N/¹⁵N-peptide ratios of 248 lens proteins, including Crystallin, Aquaporin, Collagen and enzymes that catalyze glycolysis and oxidation/reduction reactions. Direct comparison of lens cortex versus nucleus revealed little or no ¹⁵N-protein contents in most nuclear proteins, while there were a broad range of ¹⁴N/¹⁵N ratios in cortex proteins. Unexpectedly, like Crystallins, many enzymes with relatively high abundance in nucleus were also exceedingly long-lived. The slow replacement of these enzymes in spite of young age of mice suggests their potential roles in age-related metabolic changes in the lens.

Lens intermediate filaments

The ocular lens assembles two separate intermediate filament systems sequentially with differentiation. Canonical 8-11 nm IFs composed of Vimentin are assembled in lens epithelial cells and younger fiber cells, while the fiber cell-specific beaded filaments are switched on as fiber cell elongation initiates. Some of the key features of both filament systems are reviewed.

Knockout of the intermediate filament protein CP49 destabilises the lens fibre cell cytoskeleton and decreases lens optical quality, but does not induce cataract

In this report, the phenotype associated with the first targeted knockout of the lens specific intermediate filament gene CP49 is described. Several surprising observations have been made. The first was that no cataract was observed despite the fact that the beaded filaments of the lens fibre cells had been disrupted. Light scatter and the lens optical properties had, however, deteriorated in the CP49 knockout lenses compared to litter mate controls. These changes were accompanied by dramatic changes in plasma membrane organisation of the fibre cells as revealed by detailed morphological examinations and providing the second surprising result. The CP49 knockout mouse is therefore an important model to study the functional link between lens transparency, the cytoskeleton and plasma membrane organisation.

A novel locus for autosomal dominant, non-syndromic hearing impairment (DFNA18) maps to chromosome 3q22 immediately adjacent to the DM2 locus

Investigating a large German pedigree with non-syndromic hearing impairment of early onset and autosomal dominant mode of inheritance, linkage to known DFNA loci was excluded and in a subsequent genomic scan the phenotype was mapped to a 10-cM interval on chromosome 3q22; a maximum two-point lod score of 3.77 was obtained for the marker D3S1292. The new locus, DFNA18, is excluded from neighbouring deafness loci, DFNB15 and USH3, and it overlaps with the recently described DM2/PROMM locus. As hearing loss has been described as one feature of the PROMM phenotype, the DFNA18 gene might also be responsible for hearing loss in DM2/PROMM.