Sperm spermatozoa

The first cell cycle of the mouse embryo differs in many respects from the second and the following cell cycles. It is characterized by a long Gl phase that starts after the penetration of the spermatozoon or artificial activation of the oocyte. During this period the chromatin of the oocyte completes the second meiotic division and forms the female pronucleus. At the same time, in the fertilized egg, the highly condensed chromatin of the sperm nucleus decondenses and sperm-specific proteins, protamines, are replaced by histones. After the initial sperm chromatin... 

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. 

Figure 3. (Upper Panel). Scanning electron micrograph of an H. rufescens spermatozoon. The sperm head, from mitochondrion (M) to tip of the acrosome vesicle (granule AV) is 7 pm. The width of the nucleus (N) is 1 pm. (Lower Panel). Transmission electron micrograph of the acrosomal vesicle showing it attached to the nucleus (NF) by the rod of actin filaments (AF). The darker material labelled 1 shows the location of the 18K protein and 2 shows the location of lysin (from Lewis et al., 1980).

The union of ovum and spermatozoon is not a process in which the sperm penetrates by virtue of its mechanical properties, but one in which a particularly intimate arul specific biochemical reaction plays the chief role. 

Until now, no experimental results support the hypothesis of a carbohydrate-mediated species-speeifie sperm binding for amphibians, similar to that demonstrated for mammalians. Further studies will probably indicate if the pattern of glycan structures found in each amphibian species represent the support for a specifie recognition of the ovule by the spermatozoon. 

Mammalian oocytes are surrounded by several layers of cells embedded in an extracellular matrix. This matrix has been shown to contain protein and hyaluronan [40]. The fertilizing spermatozoon must pass through it to reach the egg. In 1942 McClean and Rowlands demonstrated the possible role of hyaluronidase in dispersing and digesting the layers surrounding the oocyte [41]. Subsequent studies have shown that hyaluronidase is not essential, but is a helpful tool in assisting the passage of the individual sperm toward the oocyte [40],... 

Tesarik, J. 1994. How the spermatozoon awakens the oocyte Lessons from intracytoplasmic sperm injection. Hum. Reprod. 9 977-8. 

Measurement of the intrinsic motility forces of individual spermatozoa is carried out by optical trapping. Individual spermatozoa are optically trapped by means of laser tweezers, and the minimal trapping power required to hold the sperm cell in the optical trap (that is, the power below which the spermatozoon escapes from the trap) is measured ([85] and references cited therein). 

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