THE DEVELOPMENT OF PIGMENT GRANULES IN THE EYES OF WILD TYPE AND MUTANT DROSOPHILA MELANOGASTER

Abstract

The eye pigment system in Drosophila melanogaster has been studied with the electron microscope. Details in the development of pigment granules in wild type flies and in three eye color mutants are described. Four different types of pigment granules have been found. Type I granules, which carry ommochrome pigment and occur in both primary and secondary pigment cells of ommatidia, are believed to develop as vesicular secretions by way of the Golgi apparatus. :The formation of Type II granules, which are restricted to the secondary pigment cells and contain drosopterin pigments, involves accumulation of 60-to 80-A fibers producing an clliptical granule. Type III granules appear to be empty vesicles, except for small marginal arcas of dense material; they are thought to be abnormal entities containing ommochromc pigment. Type IV granules are characteristic of colorless mutants regardless of genotypc, and during the course of development they often contain glycogen, ribosomes, and show acid phosphatase activity; for these reasons and because of their bizarre and variable morphology, they are considered to be autophagic vacuoles. The 300-A particles commonly found in pigment cells arc identified as glycogen on the basis of their morphology and their sensitivity to salivary digestion.

Assembly of the cnidarian camera-type eye from vertebrate-like components

“…Vertebrate eyes use melanin as their exclusive dark pigment. However, among invertebrates, pterins constitute the eye pigment in the polychaete Platynereis dumerilii (4), pterins and ommochromes are accumulated in eyes of Drosophila (5), and melanin is found rarely such as in the inverse cup-like eyes of the planarian, Dugesia (6).…”

Eye pigments of the blood-sucking insect, Triatoma infestans klug (Hemiptera, Reduviidae)

“…Kynurenine has been detected microspectrofluorimetrically in the Malpighian tubules of T. infestans (Mello & Vidal, 1985). With the development of the insect optical system, the precursors of eye pigments discharged from the insect's hemolymph are captured by the developing eyes and transformed and deposited in pigment granules (Shoup, 1966;Colombo et al, 1973;Wigglesworth, 1984). Xanthommatin and other ommochromes are synthesized only in the eyes and in epidermal cells (Colombo et al, 1973).…”

Modification of gene suppression in Drosophila melanogaster by sex chromosomes: II. Variegation in eyes of wm4 males

“…For each fly investigated, an image of the eye was projected onto a separate sheet of graph paper at a magnification such that the total area of the eye corresponded to about 800 subdivisions. The colourless regions found in wm4/O flies were outlined; since the eye contains about 800 ommatidia (Shoup, 1966), the number of subdivisions within an outlined region was an approximation of the number of ommatidia it contained.…”

“…Such partially pigmented ommatidia would not have been readily detected in the present work but if there were a tendency for pigmentation to be absent from secondary pigment cells rather than randomly from both types, it might be responsible for the brownish colour we observed in wm4/O males, where the inversion affects many more ommatidia than in either Wm4/ YY or m4/ Y flies. Ommochrome is already visible in the eyes of a two-day-old pupa whereas drosopterin synthesis does not start until the third day of pupation (Shoup, 1966); an alternative interpretation for the brownish colour is that the white locus becomes inhibited after the formation of the brown but before the synthesis of the red pigment. The latter speculation makes certain predictions as to the timing of the control of pigment formation which should be testable.…”

“…Two main types of pigment are normally present: a red pigment believed to be made up of three closely related compounds, the drosopterins (Ziegler and Harmsen, 1969) and a brown pigment, which is an ommochrome belonging to the ommatin class (Dickinson and Sullivan, 1975). According to Shoup (1966), the granules bearing the ommochromes are present in primary and secondary pigment cells whereas the drosopterin-bearing granules are restricted to the secondary pigment cells. In a histological study of eye-pigmentation, Nolte (1950) observed that the pigment granules in wm4 males with the standard sexchromosome constitution are morphologically the same as those in the wild type but can be absent in some of the normally pigmented cells within a given ommatidium.…”