BFSP2 is a

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

that encodes the

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...

phakinin ("beaded filament structural protein 2") in humans. More than 99% of the vertebrate

ocular lens An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is named because it is usually the lens that is closest to the eye when someone looks through the device. The ...

consists of

terminally differentiated Cellular differentiation is the process in which a stem cell alters from one type to a differentiated one. Usually, the cell changes to a more specialized type. Differentiation happens multiple times during the development of a multicellular ...

lens fiber cells. Two lens-specific intermediate filament proteins, the protein product of this gene (CP49 or phakinin) and filensin (also known as CP115), are expressed only after fiber cell differentiation has begun. Both proteins are found in a structurally unique

cytoskeletal The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is comp ...

element that is referred to as the beaded filament (BF). Mutations in this gene have been associated with juvenile-onset, progressive

cataract A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry or double vision, halos around light, trouble w ...

s and

Dowling-Meara epidermolysis bullosa simplex Epidermolysis bullosa simplex (EBS) is a disorder resulting from mutations in the genes encoding keratin 5 or keratin 14 Keratin 14 is a member of the type I keratin family of intermediate filament proteins. Keratin 14 was the first type I kerat ...

. The two BFSP proteins are put into a "type VI" of

intermediate filament Intermediate filaments (IFs) are cytoskeleton, cytoskeletal structural components found in the cells of vertebrates, and many invertebrates. Homologues of the IF protein have been noted in an invertebrate, the cephalochordate ''Branchiostoma' ...

(IF) classification. Unlike other IFs that form unbranched links, the two proteins form a network of filaments together with CRYAA.

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Further reading