Effects of telomere length in Drosophila melanogaster on life span, fecundity, and fertility

Abstract

Chromosome length in Drosophila is maintained by targeted transposition of three non-long terminal repeat retrotransposons, HeT-A, TART, and TAHRE, to the chromosome ends. The length and composition of these retrotransposon arrays can vary significantly between chromosome tips and between fly stocks, but the significance and consequences of these length differences are not understood. A dominant genetic factor, Tel, has been described, which causes a severalfold elongation of the retrotransposon arrays at all telomeres. We used this strain to assess possible affects of extended telomeres on the organism. While we found no effect on life span of the adults, we could demonstrate a correlation between long telomeres and reduced fertility and fecundity in individual females, which is also reflected in abnormal oocyte development.

Figure 1

(A) Schematic map of three telomeric retrotransposons and jockey with the positions of fragments that were specifically amplified in qPCR to determine genomic copy numbers of each element. (B) Relative copy numbers (expressed as Ct values from qPCR) of telomeric retrotransposons and jockey in the GIII and Oregon R strains with respect to the copy number of the ribosomal protein gene S17 (RpS17).

Figure 2

(A–C) Fluorescence in situ hybridizations (FISH) with a HeT-A probe to the bridged telomere-telomere association in polytene salivary chromosomes of GIII flies. (D) Immunofluorescence staining of a Tel polytene chromosome squash with anti-PROD antibody, showing association of the PROD protein with the telomeres and the bridges that connect the frequent telomere associations in this strain.

Figure 3

Survival curves of GIII, Oregon R, Canton S and y w flies at 25°C.

Figure 4

(A) Fecundity and fertility of forty GIII single pair matings; (B) Fecundity and fertility of twenty Oregon R single pair matings; (C) Average of fecundity and fertility of GIII and Oregon R pairs.

Figure 5

(A) Comparison of telomere length (black dots) (expressed as ratio of genomic copy number of HeT-A to that of the RpS17 gene) to fecundity and fertility in the G0 generation of 15 selected single GIII females crossed to Oregon R males. The designation of individual founder females (lines) is shown on the X-axis and the data are arranged according to increasing telomere length. (B) Correlation of telomere length with fertility in 15 different GIII females. Their numerical designations are the same as in (A) and are shown in the legend.

Figure 6

(A) Average fecundity and fertility of fifteen single pair matings between Oregon R pairs (first pair of columns), between GIII females and Oregon R males (second pair of columns) and between GIII males and Oregon R females (third pair of columns), indicating that longer telomeres affect the male as well as the female germ line. (B) Average fecundity and fertility of ten single females (as percent of Oregon R pairs) of GIII, prod/CyO and Su(var)205⁰²/CyO single females crossed individually to Oregon R males. Error bars show STD.

Figure 7

Correlation of telomere length (black dots, as ratio of genomic copy number of HeT-A to that of ribosomal protein gene S17) to fecundity and fertility in the G3 generation of selected single GIII females crossed to Oregon R males. In the numbering of individuals on the X-axis, the first number designates the original founder female (line), the second number the individual F3 female analyzed from this line. Females are arranged according to increasing telomere length.

Figure 8

DAPI-stained ovaries dissected from Oregon R as control (A), and from selected females in generation 3 of the original GIII founder female 61 (B, C). Female 61-4 with short HTT arrays and high fecundity and fertility (see Fig. 7) contained normal appearing ovaries (B), while female 61-7 with long HTT arrays and very low fecundity and fertility (Fig. 7) had abnormal ovaries (C) characterized by degeneration of nurse cell nuclei with their DNA irregularly condensed. Ovaries of Su(var)205⁰²/Cy females with long telomeres (D) and prod/Cy females (E), which do not have extended telomeres, revealed similar developmental abnormalities as GIII females with long telomeres (C). Arrows in C–E point to abnormal oocysts, which mostly arrested in stage 9–10. DAPI-stained normal oocysts of Oregon R, stage 9–10, are shown in (F). Abnormal oocysts of the GIII female 61-7 with long HTT arrays (G), of Su(var)205⁰²/Cy females with long telomeres (H) and of prod/Cy females (I) reveal a very similar degeneration phenotype of nurse cell nuclei. Nurse cell nuclei of Oregon R females (J) are contrasted with nurse cell nuclei of GIII females at progressive stages of DNA condensation and aggregation at the nuclear periphery (K–M).