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

Abstract

Amplification of the genes coding for rRNA occurs 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 B. germanica demonstrate a single large nucleolus instead of many nucleoli. In order to determine whether the genes coding for rRNA are amplified in the oocyte of B. germanica, the relative amount of r[ribosomal]DNA in oocytes is 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 .apprx. 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 1 end of the X chromosome and that oocytes do not contain more than twice the amount of rDNA found in spermatocytes. rDNA is probably not amplified in the uninucleolate oocyte of B. germanica.