Arginine 54 and Tyrosine 118 residues of {alpha}A-crystallin are crucial for lens formation and transparency.
OBJECTIVE
To identify new mouse models for studying roles of alphaAlpha-crystallin in vivo and to investigate why and how different mutations of the alphaAlpha-crystallin gene lead to dominant or recessive cataracts.


METHODS
Using mouse genetic approaches and slit lamp screening, we identified two mouse cataractous mutant lines. Causative genes were mapped by a genome-wide linkage analysis. DNA sequencing verified missense mutations of alphaA-crystallin gene in both mutant lines. Histology, imaging of green fluorescent protein (GFP)-positive lenses, and protein 2-DE gel were used to determine the morphologic and biochemical properties of mutant lenses.


RESULTS
Two new alphaA-crystallin gene mutations were identified, alphaA-R54C (alphaA-Cys) and alphaA-Y118D, which cause recessive whole cataracts and dominant nuclear cataracts, respectively. In homozygous alphaA-Cys mutant mice, lens epithelial and fiber cells lost their characteristic cellular features and developed disrupted subcellular structures, such as actin filaments and mitochondria. The nuclear cataract caused by alphaA-Y118D mutation was associated with increased water-insoluble crystallins (alpha, beta, and gamma classes). These results suggest that the Arg54 residue in the N-terminal region is crucial for alphaA-crystallin to perform its roles in lens epithelial and fiber cells during development, whereas the Y118D mutation in the central alpha-crystallin domain impairs alphaA-crystallin's ability to maintain the solubility of crystallin proteins in the lens.


CONCLUSIONS
This work demonstrates that different regions of alphaA-crystallin mediate distinct functions in vivo. These two mutant mouse lines provide useful animal models for further investigating the multiple roles of alphaA-crystallin in the lens.
Xia
Chun-hong
CH
School of Optometry and Vision Science Program, University of California, Berkeley, Berkeley, California 94720-2020, USA.
Liu
Haiquan
H
Chang
Bo
B
Cheng
Catherine
C
Cheung
Debra
D
Wang
Meng
M
Huang
Qingling
Q
Horwitz
Joseph
J
Gong
Xiaohua
X
D000199:Actins / Q000378:metabolism; D000818:Animals; D001120:Arginine / Q000502:physiology*; D002386:Cataract / Q000235:genetics* / Q000473:pathology; D002874:Chromosome Mapping; D004195:Disease Models, Animal; D015180:Electrophoresis, Gel, Two-Dimensional; D004847:Epithelial Cells / Q000502:physiology; D005260:Female; D005799:Genes, Dominant; D005808:Genes, Recessive; D008040:Genetic Linkage; D049452:Green Fluorescent Proteins; D007908:Lens, Crystalline / Q000502:physiology*; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000473:pathology; D010641:Phenotype; D017354:Point Mutation; D014443:Tyrosine / Q000502:physiology*; D038202:alpha-Crystallin A Chain / Q000235:genetics*
D000199:Actins; D038202:alpha-Crystallin A Chain; D049452:Green Fluorescent Proteins; D014443:Tyrosine; D001120:Arginine