Spermiogenesis in the Korean Squirrel, Tamias sibiricus

Spermiogenesis in the Korean squirrel, Tamias sibiricus, was investigated by transmission electron microscopy. Spermiogenesis was divided into Golgi, cap, acrosome, maturation and spermiation phases based on the characteristics of acrosomal changes and nuclear shape. Beside, the Golgi, cap and acrosomal steps were subdivided into three phases of early, middle and late phase respectively, the maturation step was divided into two phases of early and late phase, and spermiation step has only one phase. Thus, the spermiognesis of T. sibiricus was divided into a total of twelve phases. In Golgi phase (steps 1-3), a well developed Golgi complex was located close to the vesicles, the acrosomal vesicle fixd to a recess of nuclear membrane at step 3. During cap phase (steps 4-6), the acrosomal vesicle spred over the nuclear surface to cover a third of the nucleus, and the acrosomal granule was not yet flattened. At acrosomal phase (steps 7-9), the nucleus and acrosome were elongated but nucleoplasm was not condensed. During maturation phase (steps 10-11), the nucleoplasm was more condensed, and the mitochondria completely arranged the center of axoneme. The spatulate-sperm head was completely formed at spermiation phase (step 12).