Practice question

Delta-crystallin, first lens-specific protein to accumulate in chick and reptile lens, functions as major soluble structural protein contributing to high refractive index and transparency. Encoded by duplicated argininosuccinate lyase gene co-opted for lens function, it packs densely in fiber cell cytoplasm without organelles, minimizing light scatter. L-Maf and Pax6-Sox2 complex transactivate its promoter. Unlike enzymes, its role in lens is largely structural, filling fiber cells with uniform, water-soluble, stable oligomers that maintain transparency and correct focusing, not in retinal formation, signaling inhibition or inducing differentiation indirectly.