Distribution of the Microtubule-Dependent Motors Cytoplasmic Dynein and Kinesin in Rat Testis1

Abstract

To examine the possible role of microtubule-based transport in testicular function, we used immunofluorescent techniques to study the presence and localization of the microtubule mechanoenzymes cytoplasmic dynein (a slow-growing end-directed motor) and kinesin (a fast-growing end-directed motor) within rat testis. Cytoplasmic dynein immunofluorescence was observed in Sertoli cells during all stages of spermatogenesis, with a peak in apical cytoplasm during stages IX-XIV. Cytoplasmic dynein immunofluorescence was also localized within Sertoli cells to steps 9-14 (stages IX-XIV) germ cell-associated ectoplasmic specializations. In germ cells, cytoplasmic dynein immunofluorescence was observed in manchettes of steps 15-17 (stages I-IV) spermatids, and small, hollow circular structures were seen in the cytoplasm of step 17 and step 18 spermatids during stages V and VI. Kinesin immunofluorescence was observed in manchettes of steps 10-18 spermatids (stages X-VI). The stage-dependent apical Sertoli cell cytoplasmic dynein immunofluorescence, in conjunction with the previously reported orientation of Sertoli cell microtubules (slow-growing ends toward the lumen) and peak secretion of androgen-binding protein and transferrin, is consistent with the hypothesis that cytoplasmic dynein is involved in Sertoli cell protein transport and secretion. Further, the localization of cytoplasmic dynein and kinesin to manchettes is consistent with current hypotheses concerning manchette function.

Intracellular Localization of the Microtubule-Associated Motor Proteins Kinesin and Cytoplasmic Dynein in Rat Sertoli Cells.

“…This result was virtually identical to that of Hall et al [17]. In Sertoli cells, microtubules are aligned parallel to the long axis of the cells with their minus-end pointed toward the lumen.…”

“…Cytoplasmic dynein and kinesin transport organelles toward the minus and plus ends of microtubules, respectively. In rat testes, the distribution of these motor proteins has been observed [17], and cytoplasmic dynein was detected in Sertoli cells throughout all stages, while kinesin was localized only in spermatogenic cells [17]. However, the exact intracellular localization of microtubule-associated proteins in the cells still remains unclear.…”

A complex containing α6β1-integrin and phosphorylated focal adhesion kinase between Sertoli cells and elongated spermatids during spermatid release from the seminiferous epithelium

“…Microtubules, apart from providing structural support, play an important role in the translocation of elongated spermatids from deep within Sertoli cell crypts up to the tubule lumen at the onset of spermiation (Amlani & Vogl 1988, Russell et al 1989, see Vogl et al 1993. Microtubules are attached via motor proteins (kinesin and dynein) to the endoplasmic reticulum side of the ES in Sertoli cells (Hall et al 1992, Miller et al 1999. Immunohistochemical localisation of a-tubulin also suggests that microtubules may be present during spermiation (Wenz & Hess 1998), however, whether microtubules are present at the time of spermatid release or are involved in spermatid retention during spermiation failure is unclear.…”

Association of Kinesin Light Chain with Outer Dense Fibers in a Microtubule-independent Fashion

“…Verhey et al (11) hypothesized that cargo binding triggers a conformational change resulting in microtubule binding of the activated kinesin. As described in the Introduction, several kinesins and KRPs have been detected in sperm, including kinesin associated with the manchette, a transient microtubule structure (50); KRPs (21,22); kinesin II, a KIF3-based motor molecule (27); and KAP3 (51). It is important to note that kinesin II, which was found in the midpiece, consists of two different KIF3 motor proteins linked to the dynactin component Glued (52,53) and lacks conventional KLC.…”