Nucleolar organization in oocytes of gryllid crickets: subfamilies Gryllinae and Nemobiinae

Formation and function of accessory nuclei in the oocytes of the bird louse, Eomenacanthus stramineus (Insecta, Mallophaga). I. Ultrastructural and histochemical studies

In the oocytes of Eomenacanthus stramineus accessory nuclei arise by budding from the nuclear envelope. It is suggested that microtubules and the thick layer of the nuclear lamina are involved in this process. Newly formed accessory nuclei contain aggregations of fibrillogranular material. These aggregations are slightly Feulgen positive, RNA negative and stain positively with the Ag-NOR method. During later developmental stages one dense, RNA-positive inclusion appears in each accessory nucleus. These inclusions consist of an Ag-NOR-positive cortical layer and an Ag-NOR-negative core. The function of accessory nuclei in the species investigated is discussed in the light of these results.

Absence of rDNA amplification in the uninucleolate oocyte of the cockroach Blattella germanica (Oorthoptera: Blattidae)

Amplification of the genes coding for ribosomal RNA oocurs in the oocytes of a wide variety of organisms. In oocytes of various species of crickets (Orthoptera: Gryllidae) the amplified DNA is contained in a large extrachromosomal DNA body. Multiple nucleoli form about the periphery of the DNA body during the diplotene stage of meiosis I. In contrast to the general pattern of orthopteran oocytes, oocytes of the cockroach Blattella germanica demonstrate a single large nucleolus instead of many nucleoli. In order to determine whether the genes coding for rRNA are amplified in the oocytes of B. germanica, the relative amount of rDNA in oocytes was compared with the rDNA content of spermatocytes and somatic cells. An extrachromosomal DNA body similar to that present in crickets is not present in B. germanica. A satellite DNA band which contains nucleotide sequences complementary to rRNA accounts for approximately 3-5% of the total DNA in somatic and in male and female gametogenic tissues. Female cells contain approximately twice as much rDNA as do male cells. An XX-XO sex-determining mechanism is operative in B. germanica. In situ hybridization with rRNA indicates that the nucleolar organizer is located on one end of the X chromosome and that oocytes do not contain more than twice the amount of rDNA found in spermato cytes. The data indicate that rDNA is not amplified in the uninucleolate oocyte of B germanica.

Extrachromosomal DNA and RNA-synthesis in oocytes of Creophilus maxillosus (Staphylinidae, Coleoptera, Polyphaga)

It has been found that the transcriptional activity of nuclear extra DNA in Creophilus maxillosus oocytes, as examined by autoradiography, increases parallel with its dispersion during the previtellogenic period of oocyte growth. The RNA, after being synthesized in the greatly enlarged oocyte nucleus, is subsequently transported into the cytoplasm. The oocyte chromosomes form a karyosphere and synthesize the RNA more weakly than other parts of the nucleus, which contain the extra DNA in a highly dispersed condition.

Localization of ribosomal DNA within oocytes of the house cricket, Acheta domesticus (Orthoptera: Gryllidae)

A large DNA-containing body is present in addition to the chromosomes in oocytes of the house cricket Acheta domesticus. Large masses of nucleolar material accumulate at the periphery of the DNA body during the diplotene stage of meiotic prophase I. RNA-DNA hybridization analysis demonstrates that the genes which code for 18S and 28S ribosomal RNA are amplified in the ovary. In situ hybridization indicates that the amplified genes are localized within the DNA body of early prophase cells. As the cells proceed through diplotene the DNA which hybridizes with ribosomal RNA is gradually incorporated into the developing nucleolar mass.