Ultrastructure of sertoli‐cell penetrating processes found in germ cells of the golden‐mantled ground squirrel (Spermophilus lateralis)

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Abstract
We have studied the ultrastructure of Sertoli‐cell processes that extend into developing germ cells of the ground squirrel (Spermophilus lateralis). In other mammals it is speculated that these processes anchor germ cells to the seminiferous epithelium and transfer materials between Sertoli and germ cells. In the ground squirrel, Sertoli‐cell projections first appear in round spermatids and consist of regions containing numerous mitochondria and intermediate filaments together with areas composed mainly of a fine filamentous matrix. Also present are what may be desmosomelike junctions with adjacent germ cells. During spermatogenesis, numerous changes in the penetrating processes and their internal composition occur. Especially significant are those occurring during the movement of residual cytoplasm basaly over spermatid heads: some Sertoli‐cell processes contain microtubules, mitochondria and vesicular elements, but also present are regions that lack organelles and appear simply as thin lamellae of cytoplasm that line cavernous invaginations of the germ cell. Coated vesicles and pits are present in processes and adjacent germ‐cell regions at all stages of spermatogenesis. Our observations are consistent with the suggestions that Sertoli‐cell processes have an attachment function and that they also may facilitate the movement of residual cytoplasm into the epithelium. Further, they indicate that these structures might be involved with receptor‐mediated edocytosis.