Accessory nuclei in insect oogenesis: in search of the function of enigmatic organelles

Abstract

This review compiles present knowledge of the structure and molecular composition of the enigmatic cytoplasmic organelles called accessory nuclei. Most typically, they are found in the perinuclear cytoplasm in oocytes of insects and several other invertebrates. Accessory nuclei originate by budding of the oocyte nucleus (germinal vesicle) and are surrounded by an enelope identical to the nuclear envelope. They contain one or several dense inclusions called pseudonucleoli immersed in a translucent ground substance or matrix. Comparative analysis of the morphology, molecular composition and the ultimate fate of accessory nuclei and their inclusions revealed that there are two basic types of these organelles in insect oocytes. In mallophagans, accessory nuclei are associated with the oocyte nucleus throughout entire oogenesis and at least some of them are connected to the germinal vesicle by slender stems. Each accessory nucleus contains a single, dense, RNA-positive inclusion which is likely to correspond to a nucleolus. In hymenopterans, accessory nuclei initially surround the germinal vesicle but during oogenesis they separate from it and migrate toward the peripheral ooplasm. Within the accessory nucleus matrix usually two distinct inclusions develop. One of these is perfectly spherical, contains coilin and small nuclear ribonucleoproteins and is homologous to the Cajal body. In the light of recent discoveries, we discuss the role accessory nuclei play in insect oogenesis and early embryogenesis.

Assembly of RNP granules in stressed and aging oocytes requires nucleoporins and is coordinated with nuclear membrane blebbing

“…The nuclear membrane blebs in arrested and stressed oocytes described here are somewhat reminiscent of the accessory nuclei (AN) described in hymenopteran insects (Jaglarz et al, 2008). Accessory nuclei bud from the oocyte nucleus and are surrounded by membrane identical to the nuclear envelope including the presence of nuclear pores.…”

Previtellogenic and vitellogenic oocytes in ovarian follicles of cultured siberian sturgeon Acipenser baerii (Chondrostei, Acipenseriformes)

“…The Cajal bodies, recently renamed histone locus bodies, are engaged in the formation of spliceosomal snRNAs in X. laevis (Gall et al, ; Kambach et al, ; Handwerger and Gall, ; Nizami and Gall, ; Machyna et al, ). Nuclear bodies that contain snRNPs are also present in nuclei and in accessory nuclei in oocytes of insects (Jaglarz, ; Stepanova et al, ; Jaglarz et al, ; Bogolyubov et al, ).…”

An ultrastructural study of the ovary cord organization and oogenesis in Erpobdella johanssoni (Annelida, Clitellata: Hirudinida)

“…Although the karyosome is regarded as a structure of low transcriptional activity, the GV may still be a dynamic organelle. Numerous studies have shown that GVs in organisms with a meroistic mode of oogenesis may possess such structures as extra-DNA bodies (extrachromosomal DNA bodies), multiple nucleoli, different kinds of nuclear domains (referred to loosely as nuclear bodies) of a different molecular composition and function, moreover GVs may be engaged in the formation of peculiar organelles that are termed accessory nuclei (for references, see Bogolyubov and Parfenov, 2008;Jaglarz et al, 2008). In the present study, we have found that in E. johanssoni meiotic chromosomes condense into the karyosome during early previtellogenesis.…”