Ultra-differentiation of Sperm Head in Lesser Egyptian Jerboa, Jaculus jaculus (Family: Dipodidae)

In the present study, events of sperm head differentiation in Lesser Egyptian Jerboa, Jaculus jaculus were studied for the first time. Adult males of J. jaculus were collected during their period of sexual activity from sandy regions of Marsa-Matrouh at northwest of Egypt. Tissues of their testes were prepared for ultrathin sections, which examined under a Joel "JEM-1200EXII" operating at 60-70kv. Early and late spermatids were photographed to describe the successive stages of sperm head differentiation. Early spermatids have rounded or oval nuclei with fine chromatin granules and their cytoplasm showed numerous mitochondria, one or more chromatoid bodies and segments of rough endoplasmic reticulum. The first stage of spermatid development usually starts when the Golgi body produces secretory vesicles. These vesicles usually differentiate into an oval dense acrosomal granule, the rest forming a thin layer of acrosomal cap which extends to cover the anterior half of the nucleus and stop on at the nuclear shelf in the equatorial nuclear region. This cap is separated from the nuclear envelope by a narrowed subacrosomal space. Novel and complex structures are observed in the developing acrosome, which is, the crown, anterior, and posterior acrosomal segments, anterior and posterior acrosomal caps, as well as a long dorsal and a short ventral acrosomal caps; posterior subacrosomal spaces and subacrosomal cone at the tip of the elongated nucleus. Cytoskeletal elements are responsible for re-shaping of the nucleus. A light comprehensive strength of cytoskeletal elements usually induces nuclear prolongation and formation of implantation fossa that appears in the ventrodorsal region at the posterior side of the nucleus. Manchette microtubules, solitary microtubules, and microfilaments may generate gentle compressive strength to accelerate nuclear prolongation. Manchette microtubules, which disposed of parallel to one another and to the long axis of the nucleus, could exert the force, required to produce the spermatid nucleus elongation forward and perhaps backward and to protect DNA during nuclear condensation. A translucent space appears to surround the posterior half of the nucleus in order to mitigate the pressure on the nucleus and regulate the elongation with the protection of genetic material during nuclear condensation. Worth mentioning, that the translucent perinuclear space is a unique structure was not described or discussed before.