Annulate lamellae

Abstract

This chapter discusses the microscopic structure of annulate lamellae. Cytoplasmic annulate lamellae usually present themselves as stacks of cisternae, the edges of which tend to be slightly or markedly dilated. The annulate lamellae bear a close resemblance to the structure of the nuclear envelope. The appearance created is that of segments of nuclear envelope stacked in parallel arrays in the cytoplasm. Such stacks may be scattered in the cytoplasm or lie in the juxtanuclear position. The cytoplasmic annulate lamellae may be formed from fragments of nuclear envelope left behind after mitosis, by delamination from nuclear envelope with the nuclear envelope serving as a mould or template, or from a large evagination of the outer membrane of the nuclear envelope that later becomes infolded to form the cisternae of the annulate lamellae. Intracytoplasmic annulate lamellae have been seen in a large number of vertebrate and invertebrate oocytes, spermatocytes, embryonic cells, and cells of juveniles. The difficulty of isolating annulate lamellae precludes biochemical analysis, and this hampers the ability to probe the function of this organelle.