Development of the endoplasmic reticulum during human spermatogenesis.

Human primary spermatocytes show a special development of the endoplasmic reticulum (ER). During the leptotene-zygotene stages a cisterna of ER surrounds a third or half of the nucleus closely associated with the nuclear envelope and connected with it. In the following stages of the first meiotic prophase, stacks of these cisternae appear closely related to the nucleus and show connections with other cytoplasmic cisternae which are free in the cytoplasm. In the secondary spermatocytes and spermatids, the number of ER cisternae joined to the nucleus decreases; in contrast, the number of free ER cisternae increases. Another peculiar differentiation of the ER, such as the annulate lamellae (AL), appears in the late stages of the first meiotic prophase in relation with the nuclear envelope. AL are conspicuous in secondary spermatocytes and spermatids. In spermatids, AL appear either joined to the nucleus or free in the cytoplasm, in close proximity to the Golgi complex. Finally, AL and other membranes of the ER are released in the cytoplasmic droplets of the maturing spermatids.