Table II.
Axonemes and sperm production in males expressing β2 or variant β-tubulins
| β-tubulin in axonemesa | Axoneme morphologyb | Maximum spermatid cyst length (μ=m)c | Mature motile sperm producedd | Length of motile sperm (μ=m)e | Male Fertilityf |
|---|---|---|---|---|---|
| β2 Wild type | Normal 9+2 | 1952 (15) | Normal amounts (25/25) | 1754 (10) | Fertile (29/29) |
| One copy β2 (50% tubulin pool) | Normal 9+2 | 1656 (18) | Reduced amounts (20/22) | 1551 (13) | Fertile, reduced 37% (27/27) |
| β2ΔC | No axonemes made | 927 (11) | None | Sterile | |
| β1 | Proximal: 9+0; Distal: axonemes absent | 874 (19) | None | Sterile | |
| β2 and β1 | Normal 9+2 | 1917 (5) | Normal amounts (20/20) | 1792 (11) | Fertile, slightly reduced 68% (31/34) |
| β2β1C | Proximal: 9+2 (57%); 9+0 (43%); Distal: axonemes fragmented or absent | 1240 (5) | None | Sterile | |
| β1β2C | Proximal: 9+2 (47%); 9+0 (53%); Distal: axonemes absent | 445 (10) | None | Sterile | |
| β2β1C and β1β2C | 9+2 (95%); 9+0 (5%); Some axonemes defective or fragmented | 1674 (15) | Small amounts (31/125) | 1814 (6) | Sterile to very weakly fertile 5% (4/45) |
Except for males with only one copy of β2, data are for males with two β-tubulin genes and normal tubulin pool size. Males expressing β2 and β1, or β2β1C and β1β2C, had one gene copy of each; both β-tubulins were co-incorporated into testis microtubules, including sperm axonemes (Fig. 2). The transgenic constructs used were all previously characterized and are described in experimental procedures.
Axoneme morphology in males co-expressing β2β1C and β1β2C was determined in this study. Axoneme morphology in other experimental genotypes was described previously (see references for transgenic constructs in experimental procedures). Normal sperm axoneme morphology is 9+2 (Fig. 2). Proximal axoneme morphology indicates morphology in cross sections of intact axonemes as initiated at the basal body. Distal fragmentation or absence of axonemes reflects failure to maintain longitudinal stability [Nielsen et al., 2001; Nielsen and Raff, 2002; Popodi et al., 2008].
Drosophila spermatids develop in syncytial cysts that elongate during spermatogenesis. Cyst elongation requires microtubule function (see text), and membrane recruitment [Ghosh-Roy et al., 2004], which was normal in all genotypes in this study. Average of the maximum cyst length per male is shown; number of males scored in parentheses.
Numbers in parentheses show the number of males that had motile sperm of the total scored. Amounts indicate amount of sperm in seminal vesicles of males that had motile sperm relative to wild type.
Average sperm length is shown for 3–5 sperm per male; number of males shown in parentheses. Sperm length approximates axoneme length (sperm nucleus, 7 μm).
Numbers in parentheses show the number of males with progeny per total number of males tested. Average number of progeny for males that gave progeny is given as a percent of the progeny produced by control wild type males in the same experiment.