DNA content of haploid and diploid nuclei in a male XO type bug

Abstract

Summary. The DNA content of sperm, spermatide, and brain cell nuclei was determined by Feulgen microspectrophotometry in Dysdercus intermedius. Both in haploid and diploid cells 2 classes of DNA content were found. The differences are due to a large X chromosome in this male XO type bug. The absolute amounts of DNA represented by the X chromosome and the complete genome were calculated.Sex determination of the XO type was discovered in a bu~g in 1890 by Henking 2 and later described in several insects ~. In Lepidoptera the female is the ZO type; in Orthoptera, Hemiptera and Heteroptera the male is the XO typed heterogametic sex 4. It is assumed that such karyotypes evolved from XY ancestors by translocation or Robertsonian fusion of the Y chromosome 5. In Drosophila the small heterochromatic Y chromosome carries only a few genes concerned with male fertility 6. The transcriptional activity is restricted to spermatogenesis 7'8. On the other hand, many genes are located in the large X chromosome including loci for sex determination and oogenesis 9. The X chromosome contributes 18% of the haploid genome DNA in Drosophi- cus intermedius, and calculated the X chromosome value in this male XO type insect.Material and methods. Sperm, spermatides, and brain cells were isolated from adult bugs of the laboratory strain. The cells were lysed in 0.5% Triton X 100 solution to which 200 mg/1 spermidine phosphate (Sigma, Miinchen) had been added to stabilize the nuclear membranes. The nuclear preparations were air-dried on chromalum-coated slides and postfixed in ethanol/acetic acid 3 : 1 for 30 min. Hydrolysis was performed in 5 N HC1 for 40 min at 21 + 1 ~ The Feulgen reaction and microspectrophotometric DNA determination at 560 nm wavelength using a Zeiss UMSP II 9 12were done as routine techniques . For each type of nucleus two or more bugs were used; 2 slides were made from each bug. Each nucleus was measured 3-4 times and the average extinction was calculated. The data were processed on a Zeiss Kontron IBAS I system.