Reference: Bitil. Bull. 175: 397-402. (December. 1988) Biochemical Characteristics of the Pigmentation of Mesopelagic Fish Lenses MARGARET MCFALL-NGAI 1 *. LIN DING 1 . JAMES CHILDRESS 2 , AND JOSEPH HORWITZ 1 [ Jules Stein Eye Institute, University of California, Los Angeles, California 90024, and 2 Department of Biological Sciences, University of California. Santa Barbara, California 93106 Abstract. We analyzed the biochemical, anatomical, and spectrophotometric characteristics of lens pigmenta-tion in representatives of two mesopelagic fish families, the Opisthoproctidae and the Scopelarchidae. In small and large specimens of the opisthoproctid Macropinna microstonw and in the larval scopelarchid Benthalbella infans, the lens pigment was present in all layers of the lens as a freely diffusable chromophore. In contrast, the lenses in the adult specimens of the scopelarchid Ben-thalhella dent at a. which have lenses averaging 6.7 mm in diameter, had a 2.4 mm-diameter pigmentless core. In this species, the chromophore was bound to one of the major structural proteins of the lens, gamma crystallin. Because the lens grows by the layering of new cells over older ones, such a pattern in B. dentata suggests that the lens pigment is not present in larvae of this species. The chromophores of all specimens were characterized by a single broad peak in the shorter-wavelength blue, near-UV portion of the spectrum. Introduction Pigmentation in the tissues of vertebrate and inverte-brate visual systems is a common phenomenon, express-ing itself most often in the cornea, lens, and retinal-asso-ciated cells (Muntz, 1972; Heinermann, 1984). In the lens, pigmentation occurs: ( 1) in many diurnally active animals (Walls and Judd. 1933; Cooper and Robson 1 969a; Muntz, 1 974). including both terrestrial and shal-low water aquatic species; (2) as an age-related yellowing Received 8 August 1988; accepted 26 September 1988. * Address all correspondence to M. McFall-Ngai. Department of Bi-ological Sciences. University of Southern California. Los Angeles. Cali-fornia 90089-0371. of the lens, which occurs in vertebrate species of long life-span, independent of habitat (Cooper and Robson. 1969b;Zigman. 1971; Villermet and Weale. 1972); and (3) as a rare occurrence among animals in the mesope-lagic zones of the ocean (from about 100-1000 m depth) (see for review, Heinermann. 1984). The three types of lens pigmentation differ in their bio-chemical characteristics, their ontogenic pattern in the animal, and perhaps also in their function. In diurnally active animals, the lens pigment is present at all stages in the animal's life history as a soluble component of the lens cells; i.e., it is freely diffusible through the numerous gap junctions between adjacent cells in the lens. Lenticu-lar coloration in these species is thought to increase vi-sual acuity by reducing chromatic aberration produced by the shorter wavelengths. In age-related pigmentation of the lens, while young lenses may be nearly colorless, yellowing intensifies with age. The older central portion of the lens is yellower than the younger, more peripheral lens layers (Mellerio. 1987). This age-associated yellow-ing of the lens probably results from accummulated, UV-induced modifications of the lens structural proteins, or crystallins, and may have no adaptive value (Zigman, 1971). The chromophores that occur in the lenses of di-urnal animals and in the aging lens have simple spectra with absorbances in the short-wavelength blue and near-UV region of the spectrum. A recent study of the spec-troscopy, ontogeny, and biochemistry of lens pigmenta-tion in deep-sea hatchetfishes (Family Sternoptychidae) revealed a completely different pattern of pigmentation from those patterns reported for the more common types of lens pigmentation (McFall-Ngai el a/.. 1986). Lens pigmentation in the deep-sea hatchetfish has an abrupt, age-dependent onset. It begins when the fish is about 38 mm SL (maximum SL about = 90 mm), and is restricted 397



Biochemical Characteristics of the Pigmentation of Mesopelagic Fish Lenses

Margaret Mcfall-Ngai, Lin Ding, James Childress and Joseph Horwitz
Biol Bull 175: 397-402 (1988)

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