Spermatozoa membrane

Fertilization is the fusion of the sperm and ovum. The sperm head binds to the plasma membrane of the egg (oolemma), and the entire spermatozoon enters the cytoplasm of the ovum. Only capacitated spermatozoa with intact acrosomes can enter and pass through the cumulus oophorus. The acrosome is a membrane-bound, cap-like structure covering the anterior portion of the sperm nucleus. The acrosomal reaction is the release of materials that lyse the glycoprotein coat (zona pellucida) surrounding the ovum. This is necessary for fertilization to take place. Before undergoing the acrosomal reaction, sperm go through a type of hypermotility called hyperactivation. The... 

Microtubules occur in a single row below the plasma membrane of spermatozoa, although their distribution varies in different species (171). In H. diminuta and the Cyclophyllidea (Fig. 7.2), in general, they completely encircle the spermatozoon (171,212,835), often exhibiting helical periodicity. In Phyllobothrium gracile (Fig. 1.2(b)) the cortical microtubules may be confined to two demi-circles, lateral or external to the axonemes (561,564). The significance of these different distributions of microtubules in relation to potential sperm activity is not known. 

An example of the use of a highly specialised cell type to study targeted toxic effects on the cellular metabolism is the recently developed boar spermatozoon motility inhibition test (Andersson et al., 1998). The motility of a spermatozoon depends on the integrity of mitochondrial functions, and thus the action of toxins affecting the energy metabolism is very rapidly detected as reduction of motility. Other end points that can be measured are plasma membrane integrity, astrodome function, and total cellular ATP and NAD reduction. This test has been particularly useful in the detection of certain types of bacterial toxins from various enviromnental and food sources. 

The cytoplasmic droplet in bull and ram serum is spherical with a diameter of approximately 3 /x. When viewed by phase contrast microscopy, it has a dark granulated region electron microscopy reveals that this region consists of vesicles and membranous or tubular structures. The concentration of acid phosphatase in droplets is 4.3 /xg nitrophenol liberated per hour per 10 particles, much higher than the activity, 0.2 /xg nitrophenol liberated per hour per 10 spermatozoa. Ribonuclease, acid protease, y3-glueuronidase showed similar ratios. Dott and Dingle (D14) submitted additional information which indicated that in the bull and, to a lesser extent in the ram, the lysosomal enzymes cease to be associated with the spermatozoon during its maturation. 

The spermatozoon of Lingula anatina has a head (about 1.5 pm long), a midpiece (about 0.5 pm long) and a tail with a tapered end. In the head, a fairly large pear-shaped acrosome is present, in which an electron-dense structure (EDS) encloses the main part of the acrosome just inside the acrosomal outer membrane. The EDS has fine striations. 

Colwin, L.H. and Colwin, A.L. (1961) Changes in the spermatozoon during fertilization in Hydroides hexagonus (Annelida). 1. Passage of the acrosomal region through the vitelline membrane./o r a/ of Biophysical and Biochemical Cytology, 10,231-254. 

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