Ultrastructure of male germ cells in the testes of abalone, Haliotis ovina Gmelin

Abstract

An ultrastructural study of male germ cells in the testes of Haliotis ovina revealed that spermatogenesis could be classified into 13 stages, based on the pattern of chromatin condensation and distribution of organelles, as follows: the spermatogonium; five stages of the primary spermatocyte; the secondary spermatocyte; five stages of the spermatid; and the spermatozoa. Each spermatogonium was round or oval, with a euchromatic nucleus and prominent nucleolus. The primary spermatocytes were divided into five stages: leptotene (LSc); zygotene (ZSc); pachytene (PSc); diplotene (DSc); and metaphase (MSc). The nucleus of the LSc contained scattered small heterochromatin blocks that were increasingly thickened in the ZSc. The PSc was characterised by a bouquet pattern of heterochromatin fibres. The DSc decreased in size, resulting in close clumping of chromatin blocks, whereas in the MSc, long and large blocks of chromosomes were formed and then moved to be aligned along the equatorial region. Secondary spermatocyte showed thick chromatin blocks that appeared reticulate. The spermatid could be divided into five stages (St_1–5). The St₁ was a large round cell and its nucleus contained homogeneous chromatin granules. In St₂, the nuclear chromatin started to condense into patches. The St₃ was smaller with a round nucleus containing dark blocks of heterochromatin. The St₄ became smaller still, with a round opaque nucleus. The St₅ was the smallest round cell, with almost completely condensed chromatin. The spermatozoon had a round to barrel-shaped head that contained completely condensed chromatin covered by a conical acrosome. The posterior border of the nucleus was flanked by five large spherical mitochondria and the tail consisted of axonemal microtubules surrounded by the plasma membrane.