Abstract
Electron microscope studies were made on various tunicate oocytes at different stages of growth and development. Both the inner and outer lamellae of the perforated nuclear envelope demonstrate considerable blebbing activity. The blebs of the inner lamella detach into the nucleoplasm where they undergo a special type of fusion process resulting in the formation of numerous, usually single, differentiated annulate lamellae of various lengths. The blebbing of the outer layer of the nuclear envelope contributes to the vesicular and granular endoplasmic reticulum characteristically present in the ooplasm and perhaps to the differentiation of cytoplasmic annulate lamellae as well. Cytoplasmic stacks of annulate lamellae frequently have ribosomes associated with them. In addition, granular accumulations are sometimes observed around or between the annuli. The morphological evidence suggests that, at least in many cases, the annuli in the annulate lamellae are patent.
Highlights
The term annulate lamellae was first used by Swift (1956) to describe groups of parallel lamellae which are often, but not always, arranged in stacks in the cytoplasm (Kessel, 1963 b)
A question of considerable interest that has arisen since the discovery of pores in the nuclear cnvelope is whether or not these areas represent actual physical contact between the nucleoplasm and cytoplasm or whether this contact is mediated by thc presencc of a thin membranc or diaphragm
While many of the elcctron micrographs of the nuclear envelope of tunicate oocytes show a structure across thc pore which could be interpreted as a diaphragm, the variations in structure noted lend themselves more to an alternative explanation: namely, that the membranous structure often seen crossing the pore is not a diaphragm, but rather a portion of the nuclear membrane surrounding the pore which has been included in the plane in back or in front of the section and which by projection appears to lie across the pore
Summary
The term annulate lamellae was first used by Swift (1956) to describe groups of parallel lamellae which are often, but not always, arranged in stacks in the cytoplasm (Kessel, 1963 b). The lamellae have been observed in somatic cells (Swift, 1956; Ross, 1962; Harrison, 1962) as well as in tumor or cancer cells of various kinds (Schulz, 1957; Wessel and Bernhard, 1957; Binggeli, 1959) Far, it appears that annulate lamellae are most prominent or best developed in the cytoplasm of young cells actively engaged in growth and differentiation. The annulate lamellae possess certain structural characteristics of both the nuclear envelope and the granular endoplasmic reticulum They so closely resemble the nuclear envelope in structure that it appears in some ceils as if pieces of the nuclear envelope were placed in stacked, parallel array in the cytoplasm (Kessel, 1963 b, 1964 b). This report dealing with various tunicate oocytes records the presence of intranuclear annulate lamellae, provides information regarding the mechanisms whereby such intranuclear membrane structures arise, and describes the system of cytoplasmic annulate lamellae present
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