SPERMEIOGENESIS / SPERMETOLEOSIS

It is the gradual differentiation of a stationary rounded and undifferentiated spermatid into an active and motile sperm.

The spermatids formed as a result of maturation divisions are typical undifferentiated animal cells containing mitochondira, golgi body and centriole but with a haploid set of chromosomes.

In spermeiogenesis following changes take place -

(i) Formation of acrosome

1. The acrosome of spermatozoan is derived from golgi complex of the spermatid.
2. In a spermatid the golgi compelx is in the form of a spherical body, comprising of numerous vesicles or small vacuoles in the centre surronded by several rows of concentrically arranged cisternae.
3. As the differentaition proceeds, the arrangement of cisternae becomes irregular and one or two vacuoles enlarge to replace the vesicles.
4. Inside each large vacuole appears a small dense body, the proacrosomal granule.
5. The vacuole with its acrosomal granule enlarges in size, migrates towards the anterior pole and gets attached to the tip of elongated nucleus forming a sort of cap.
6. The proacrosomal granule enlarges further and forms the acrosomal granule.
7. It forms core of the acrosome. The vacuole loses its liquid content spreads over the acrosomal granule and half of the nucleus forming of spermatozoan.
8. The remainder of golgi body undergoes a gradual regression and is discardd as golgi rest together with the cytoplasm of spermatid.

Formation of Acrosome

(ii) Formation of Perforatorium

A rounded small pit present below the nucleus, in this part G actin and Ca++  ions are present. This spaces is called perforatorium space.

(iii) Nuclear changes

1. The nucleus shrinks by losing water from the nuclear sap and the chromosome closely packed.
2. The step is essential, since it reduces the weight of spermatozoon and enhances its motility.
3. Even RNA and other accessory materials are also removed leaving only the hereditary material.

(iv) Tail

1. The axial filament of the tail of spermatozoan is formed the centriole of spermatid.
2. The distal centriole gives rise to the axial filament of the flagellum and acts as a basal granule.
3. The proximal centriole enters the ovum along with sperm nucleus and mitotic spindle formation for the first division of the zygote nucleus.

(v) Formation of mitochondrial spiral and middle piece

1. The proximal part of axial filament and distal centriole in the middle piece of spermatozoan.
2. Gradually, these mitochondria lose their individuality and partly fuse together forming two densely packed bodies one on either side of axial filament.
3. The mitochondrial sheath provides energy and strength to the sperm when it swims or moves towards the ovum.
4. During the process of spermeiogenesis all the mitochondria of the spermatid fuse to form a nebenkern or Jensen's sheath.
5. The nebenkern provide required energy to the sperm.
6. The nebenkern along with little cytoplasm form a spiral sheath around the anterior end of the axial filament which is called as manchette.

(vi) Changes in the cytoplasm

1. During the acrosome formation cytoplasm move to backside and maximum part store in the middle piece of sperm.
2. Tail formation occurs and mitochondria's are arranged in middle piece and cytoplam arranged as manchette.

(vii) Sperm sheath

Sperm sheath is form of mucopolysaccharide. It is also called glycocalyx. This sheath probably function as antigen.