The occurrence of actinlike filaments in association with migrating pigment granules in frog retinal pigment epithelium

Abstract

In the retina of the frog and certain other animals, melanin pigment granules move in response to light so as to shield photoreceptor outer segments. The granules are contained within the cells of the pigment epithelium (PE) which lie as a continuous sheet between the neural retina and the choroid. Moderate illumination of the eye causes the melanin granules to move from a region within a PE cell body into numerous fingerlike extensions of the cell which interdigitate with the receptor outer segments. This migration takes many minutes and is reversed when the light falling on the eye increases in intensity. Several reviews are concerned with the early descriptions of this phenomenon (6,30) and with more recent experiments (1,5,19). The mechanism of the pigment granule motion is undetermined although there are studies concerning PE ultrastructure (8, 23, 31), scanning electron microscopy of the fingerlike extensions of the PE cells (27), the role of the PE in photoreceptor phagocytosis (32), the nature of the pigment granules (19), and the action spectrum of the light which induces the migration (16). This study reports the presence of a system of microfilaments associated with the pigment granules in the fingerlike extensions processes of the PE cells. We demonstrate by heavy meromyosin (HMM) labeling that the filaments are actinlike in character and suggest that these filaments could be responsible for the migration of the melanin pigment granules.

The identification and localization of actin and actin‐like filaments in lactating guinea pig mammary gland alveolar cells

“…Meshworks of filaments in alveolar cells appeared to undergo the same change in appearance. Other researchers have noted a similar appearance of decorated filaments in non-muscle cell sections containing meshworks of filaments that are lying obliquely relative to the plane of section [Le Beux and Willemot, 1978a and b;Furiya, Kumanmoto, Suzuki, Takauji, and Nagai, 1977;Murray and Dubin, 1975;Schloss, Milsted, and Goldman, 1977;Gipsin and Anderson, 19791. Sectioned cardiac muscle cells containing actin filaments never displayed a typical arrowhead pattern when incubated with HMM [Spooner, Ash, Wrenn, Frater, and Wessels, 19731.…”

Actin‐dependent motility of melanosomes from fish retinal pigment epithelial (RPE) cells investigated using in vitro motility assays

“…Since motor activity on RPE melanosomes was shown in the present study to be barbed-end directed, the polarity orientation of F-actin in RPE apical projections is important in determining which direction a barbed-end directed motor could translocate melanosomes through apical projections. Actin filaments in RPE of frog and chick form paracrystalline bundles with barbed ends distal [Murray and Dubin, 1975;Owaribe et al, 1988;reviewed in Burnside and Bost-Usinger, 1998]. It is not certain whether the polarity orientation of actin in fish RPE apical projections is the same.…”

Actinlike filaments in the neurosecretory cells of Helisoma duryi (Gastropoda, Pulmonata)

“…The presence of a similar network in a neurosecretory cell suggests that this concept is also applicable to transport of neurosecretory granules. Actin filaments are also thought to be concerned in the migration of pigment granules in the pigmented epithelium of frog retina (Murray and Dubin 1975) and in cytoplasmic streaming in Characea (Kersey et al 1976). Further data, however, are necessary to demonstrate the manner in which the microfilamentous network and non-contractile components interact, and this is hindered by the lack of a specific test for the localization of myosin (LeBeux and Willemot 1975~).…”