Primary Pigment Cells Research Articles

Histology of the Compound Eye of the Boll Weevil1,2,3

A histological study of the compound eye of the boll weevil, Anthonomus grandis Boheman, with a light microscope showed that each eye is composed of about 500 ommatidia 100–140 µ long, 27 µ in diameter at the lens, and 7 µ in diameter at the basement membrane. A single ommatidium consists of a hexagonal lens, a crystalline cone, 4 Semper cells, 2 primary pigment cells, 6 secondary pigment cells, 6 retinula cells which contribute to the formation of a central rhabdom that extends from the Semper cells to the basement membrane, and 2 basal pigment cells that surround the base of the retinula cells. The 6 axons, 1 from each of the 6 retinula cells, join and penetrate the basement membrane as a bundle. Each bundle of primary nerves converges with other bundles to form larger bundles that enter the optic ganglion.

The ultrastructure of the compound eye of a mosquito Aedes aegypti L

AbstractEach ommatidium in the mosquito compound eye consists of a dioptric apparatus and layer of retinula cells. The dioptric apparatus includes a cuticular cornea, a biconvex lens, and four cone cells. The cone cells have processes which extend into the receptor layer and terminate below the rhabdom as pigment‐filled sacs. Two primary pigment cells and an undetermined number of secondary pigment cells surround the dioptric apparatus. In the receptor layer eight retinula cells are found in each ommatidium. Six are peripherally arranged around a central one, whereas the remaining retinula cell is sandwiched between and somewhat external to two of the peripheral retinula cells. Each of the eight retinula cells possesses a well developed rhabdomere, along with the usual array of other intracellular organelles characteristic of arthropod photoreceptor cells.

Post emergence maturation of the eye of the adult black carpet beetle, Attagenus megatoma (Fab.): An electron microscope study

AbstractThe black carpet beetle, Attagenus megatoma (Fab.), has been reported to exhibit negative phototaxis immediately after emergence. In later adult life, after the period during which most oviposition has occurred, the beetles are found to be photopositive. The compound eyes of one‐day‐old (Post‐emergence) and nine‐day‐old (Post‐ovipositional) female beetles were studied by electron microscopy and a number of strong differences were found between eyes at the two ages. The corneal facets of one‐day eyes had the form of convex‐concave lenses, while those of nine‐day beetles were double‐convex lenses. The primary and secondary pigment cells of young eyes were large and contained much endoplasmic reticulum and little accessory pigment. In the older eyes the pigment cells were reduced and contained much pigment, the proportion of endoplasmic reticulum being greatly reduced by comparison with the one‐day eye. The cross‐sectional area of the rhabdom was greater in the older eye.The possible relationships between age‐related changes in eye morphology and behavioral changes during the same period are discussed.

Phenogenetic studies on visual acuity in Drosophila melanogaster

The dark-red eye colour of wild type Drosophila melanogaster is due to the presence of a brown and a red pigment in the primary and secondary pigment cells surrounding the ommatidia. The mutant gene vermilion blocks the synthesis of brown eye pigment, and the mutant gene brown blocks the synthesis of red eye pigment, so that white-eyed double mutants lack both pigments. Brown mutants which synthesize only the brown pigment shown no appreciable difference in visual acuity from the wild type, whereas there is a marked attenuation of visual acuity in double-mutant vermilion; brown flies. This is attributable to breakdown of optical separation of adjacent ommatidia due to absence of screening pigment, since bypassing the vermilion mutant block, by providing one of the missing intermediates in brown pigment synthesis, leads to almost complete restoration of visual acuity.

The development of pigment granules in the eyes of wild type and mutant Drosophila melanogaster.

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 elliptical granule. Type III granules appear to be empty vesicles, except for small marginal areas of dense material; they are thought to be abnormal entities containing ommochrome pigment. Type IV granules are characteristic of colorless mutants regardless of genotype, 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 are identified as glycogen on the basis of their morphology and their sensitivity to salivary digestion.

The ultra-structure of the developing eye of Drosophila

A description is given of the ultra-structure of the eye of Drosophila melanogaster during its development from the imaginal bud of the late larva till it attains its final form in the adult. Six markedly different types of cells develop out of the apparently uniform epithelium of the imaginal bud; namely, cone cells, retinula cells, primary pigment cells, secondary and basal pigment cells, two [inner and outer] types of hair-nerve cells. In each type of cell there is a characteristic form of cytoplasmic double-membrane structure [endoplasmic reticulum] which reaches its highest development at or just before the time at which the characteristic cell structures are being formed. In most types of cell there are indications of the participation of the nucleus, or nuclear envelope, in cell differentiation, these indications being different in the different cell types. In retinula cells and also in inner hairnerve cells there is evidence suggesting that the outer layer of the nuclear envelope may give rise directly to cytoplasmic double membranes. Several cell organelles are described for the first time, in particular the rhabdomere vesicular spheroids and the cone cell granules. In the formation of the rhabdomeres by the retinula cells, the first stages in the deposition of this structure are carried out by the plasma membrane on the cells. The presence of an eighth retinula is confirmed. The implications of the observations for our general understanding of cell activities during differentiation is briefly discussed; work already in progress with various mutants is expected to reveal new facts of interest in this connexion.

The structure of normal and mutant eyes in the blow-fly (Calliphora erythrocephala) and the development of eye pigment during pupation

1. The structure of the ommatidia of the eye ofCalliphora erythrocephala is very similar to that ofDrosophila. 2. Primary and secondary pigment cells are present, but the basal pigment cells described by Lowne could not be identified, and probably dense groups of granules in the basal expansions of the secondary pigment cells were mistaken for separate cells. 3. At 24° C. the onset of pigment formation in eyes during pupal life is at about 72 hr.; and the sequence is yellow, brown and red, but the late phase deposition of pigment, and the appearance of red granules, does not occur until a few hours before emergence, which at 24° C. is at 240 hr. after puparia formation. 4. The white-eyed mutant ofCalliphora erythrocephala, which is sex-limited and appears only in the female, has eyes normal in structure, and with the full complement of both primary and secondary pigment cells, but there is complete suppression of the formation of all pigment granules.

The effect of cold upon the development of pigment in a white-eyed mutant form of the blow-fly (Calliphora erythrocephala)

1. Pupae and mature larvae of the blow-fly (Calliphora erythrocephala) will continue to develop slowly at a temperature of 4°C. 2. White-eyed mutant females which emerge from pupae subjected to the low temperature have, at emergence, eyes of a deeper yellow colour than mutant females newly emerged from pupae which have developed at 21°C. 3. Some flies of the white-eyed mutant strain emerged after 6 months while still in the refrigerator at 4°C. These mutant females had red pigment granules deposited in the secondary pigment cells and probably also in the primary pigment cells. Red pigment granules are never formed in white-eyed mutant aemales which emerge from pupae kept at 21°C.