Functional interaction between an insulator and a Pc-dependent silencer by the example of the Mcp boundary of the <Emphasis Type="Italic">Drosophila melanogaster Abd-B</Emphasis> gene

Insulators are cis-regulatory elements that prevent improper gene activation and heterochromatin spreading. As shown previously, the boundary element, Mcp, from the regulatory region of the Drosophila melanogaster Abd-B gene, contains insulator. Here, we studied the boundary function of the Mcp insulator and showed that this function is provided by two modules. One is responsible for long-distance interactions and the capability of blocking enhancers. The other is essential for blocking Pc-dependent repression. It was observed for the first time that an insulator increased the repressor activity of a neighbor silencer.     

Prevention of pregnancy in cats using aglepristone on days 5 and 6 after mating

The aim of this study was to test for the efficacy of aglepristone treatment for prevention of early pregnancy in the cat. Eleven cats (Gr. 1) were treated with 10 mg/kg aglepristone on days 5 and 6 after mating, 17 cats (Gr. 2) were used as untreated controls. Blood samples for progesterone (P4) determination were collected from 6 cats of Gr. 1 and 9 cats of Gr. 2, respectively. Ultrasound examination on day 25 revealed no pregnancy in any of the treated cats. In both groups, P4 concentrations increased from day 5 (before treatment) to day 20 (P < 0.01). In Gr. 1, the interval between aglepristone treatment and the subsequent estrus ranged from 5-299 d [18.5 (5.2) d]. Mean interestrus interval was 205 ± 72 d in Gr. 2. Mean duration of subsequent estrus was not different to duration of estrus before treatment in Gr. 1 and in Gr. 2, respectively. Mean time between treatment and next pregnancy was 56.4 (4.7) d, ranging from 5-325 d. Pregnancy rates after the next estrus following treatment were 64 and 82% after the first and second estrus, respectively. No major treatment-related side effects were observed. In conclusion, treatment was found to be highly effective for prevention of early pregnancy.     

Complex alterations of the ribosomal gene spacers in mutant sc 8 of Drosophila melanogaster

Extreme changes in the proportions of the rDNA intergenic spacers (IGSs) have previously been demonstrated by us in the X-chromosomal rDNA array of the Drosophila melanogaster mutant sc ⁸ , where nearly all IGSs were found to be reduced in size. We have cloned different structural variants of the Xsc ⁸ ribosomal units and mapped their spacers by restriction endonuclease analysis. Most of the IGSs exhibited complex rearrangements within the subrepeated region at their 5′ terminus. The sequence data revealed the presence of an additional 100 bp subrepeat. In addition, extended deletions/substitutions down to the 18S gene were also found. Examination of the Ysc ⁸ IGS polymorphism indicates that some of the X-chromosomal IGS variants are probably the result of X-Y interchanges. The rarity of alternative recombination products implies that the overabundant deleted spacers in sc ⁸ are generated by nonreciprocal recombination. Our results demonstrate nonrandom distribution of deletional breakpoints within the “1900” region in sc ⁸ and show that the deletions do not truncate the internal IGS subregions at either breakpoint but eliminate them as discrete blocks. Received: 15 April 1997; in revised form: 8 August 1997 / Accepted: 22 August 1997     

Broken chromosomal ends can be elongated by conversion in Drosophila melanogaster

The fate of the termini of X chromosomes broken in the regulatory region of the yellow gene was followed in heterozygotes with X chromosomes carrying a point mutation inactivating the yellow gene. Each generation had a loss of about 70 terminal base pairs from the broken chromosome. However, gene conversion restoring the correct sequence at the chromosomal terminus took place with a frequency of about 1×10^–2 per generation. The average length of the conversion track was 2.7 kb. No recombination events occurred. In addition, we found that the normal functioning of the yellow body and wing enhancers located at the tip of the chromosome required about 4 kb of additional upstream sequence. Received: 8 October 1998; in revised form: 18 January 1999 / Accepted: 18 January 1999     

Ploidy levels in Beta vulgaris (red beet) plant organs and in vitro systems

The ploidy levels of the cells in different organs (leaves, petioles and roots) of red beet (Beta vulgaris L.) plants of different ages, as well as of different in vitro systems (transformed hairy roots, calli derived from leaves and rhizogenic calli), were investigated using flow cytometry. Two callus lines with red and yellow phenotypes, derived by mechanical separation of the morphologically heterogeneous rhizogenic callus, were also examined. All investigated samples experienced several cycles of endoreduplication. The older organs exhibited higher levels of polysomaty than the young ones. The highest degree of endoreduplication was found in old petiole tissue and the lowest in the red callus line (cycle values of 1.81 and 0.55, respectively). Interestingly, the callus derived from leaves did not exhibit a 2Cx peak, but was tetraploid, probably due to genetic instability, which may have been caused by prolonged cultivation under in vitro conditions. Red and yellow calli showed significantly lower polysomaty (cycle values of 0.55 and 0.59, respectively) than the primary rhizogenic callus (cycle value of 1.09). The DNA profiles of the two phenotypes differed, possibly reflecting differences in their metabolism.