Sperm selection

Figure 5-49 A DNA sequencing gel obtained using a segment of DNA from salmon sperm selected by suitable oligonucleotide primers, amplified by PCR, and sequenced with a 35S label in the primer. Four samples were used, one with each of the four dideoxy chain terminators (A, G, C, T, A, C, G, T from left to right). After electrophoresis the shorter fragments are at the lower end of the gel. The sequence of the strand complementary to the template strand whose sequence is being determined is read from the bottom of the gel. Here it starts CTATGATAC. Reproduced by permission of Amersham Pharmacia Biotech, Limited.

Sperm selection also provides females with the option of checking on potential liars, males which might have misrepresented themselves in courtship by producing hydroxydanaidal at exaggerated levels relative to their PA content. Unless such males also are able to produce exaggerated-sized spermatophores, they are likely to be found out when they are put to the test in sperm selection. 

Sperm chemotaxis is an example of a phenomenon in which the very same process serves different purposes in different species. In marine species, most if not all of the cells within a sperm population appear to be chemotactically responsive. The role of chemotaxis there is apparently to recruit as many sperm cells (spermatozoa) as possible to the egg. In humans, rabbits, and, perhaps, in mammals in general, the role of chemotaxis seemingly also involves sperm selection only a fraction of the sperm population, consisting of ripe spermatozoa that have the capacity to fertilize the egg, is chemotactically responsive and apparently recruited to the egg [28, 29, 52]. 

In view of the notion that chemotaxis is required for the selection of capacitated spermatozoa, faulty precontact sperm-egg communication may be one of the causes of male infertility, female infertility, or both. It is reasonable that, in the future, chemotaxis may be exploited as a diagnostic tool for sperm quality and male infertility and may be used as a biological sperm-selection procedure before in vitro fertilization, especially before intracytoplasmic single sperm insertion or for intrauterine insemination. Moreover, the chemotactic activity of a follicular fluid may be an effective way to monitor the possible effects of different ovulation induction protocols on the maturational status of oocytes aspirated for in vitro fertilization [2]. On the other hand, interference vwth sperm chemotaxis may represent an exciting new approach to contraception. 

Europe, the USA and Japan are under way. In these studies, semen analysis methodology and subject selection criteria have been standardised to address whether there are region-specific differences in semen quality. These data can then be used as a reference point for any studies on future decline in sperm counts. More importantly, it still remains to be demonstrated whether the reported decrease in semen quality is sufficient to compromise fertility. 

An alternative efficient approach to disperse CNTs relies on the use of synthetic peptides. Peptides were designed to coat and solubilise the CNTs by exploiting a noncovalent interaction between the hydrophobic face of amphiphilic helical peptides and the graphitic surface of CNTs (Dieckmann et al., 2003 Zoibas et al., 2004 Dalton et al., 2004 Arnold et al., 2005). Peptides showed also selective affinity for CNTs and therefore may provide them with specifically labelled chemical handles (Wang et al., 2003). Other biomolecules, such as Gum Arabic (GA) (Bandyopadhyaya et al., 2002), salmon sperm DNA, chondroitin sulphate sodium salt and chitosan (Zhang et al., 2004 Moulton et al., 2005), were selected as surfactants to disperse CNTs (Scheme 2.1). 

The ways in which the selective pressures associated with sperm competition manifest themselves are being found to be more varied than originally thought. The work reported here highlights three ways in which the situation is more complex. 

Palmer DK, O Day K, Margolis RL (1990) The centromere specific histone CENP-A is selectively retained in discrete foci in mattunaUan sperm nuclei. Chromosoma 100 32—36 Pandey NB, Marzluff WF (1987) The stem-loop structure at the 3 end of histone mRNA is necessary and sufficient for regulation of histone mRNA stabiUty. Mol Cell Biol 7 4557 559 Pehrson J, Fuji RN (1998) Evolutionary conservation of histone macroH2A subtypes and domains. Nucl Acids Res 26 2837-2842... 

The key objective of our efforts has been to develop a vaginal formulation that optimizes spermicidal and antiviral activity while enhancing spreading and true bioadhesiveness. Utilization of strict design principles for an excipient delivery vehicle, which included substantivity to vaginal mucosa, saline compatibility, compatibility with a wide range of spermicidal and antiviral compounds, low irritation potential, sperm impedance, system stability, and efficacy after stressed storage conditions, resulted in the development of DCE s [11,12,13]. Based on the results from in vitro studies, the DCE vehicle was selected for clinical development. 

Much of the behaviour of humans and society as a whole is designed to provide an opportunity for a sperm and an ovum to meet in the uterus. However, sexual reproduction is not the only means of reproduction asexual reproduction occurs frequently in the animal kingdom and in many tissues in order to increase the number of cells during growth or to maintain the number due to cell death. The question arises, therefore, why sexual reproduction has arisen at all since it is very expensive in the use of resources for example, in the process of selecting a suitable mate, and in the requirement for males, whose only function in some species is fertilisation of the females, yet they use resources that could be used by the females and by the offspring. Perhaps because of this, a few species of vertebrates (e.g. some lizards) have retained the option for asexual reproduction. This process is known as parthenogenesis. Mammals, however, have lost this option. This... 

Tanphaichitr, N., Sobhon, P., Taluppeth, N., and Chalermisarachai, P. (1978) Basic nuclear proteins in testicular cells and ejaculated spermatozoa in man. Exp. Cell Res. 117, 347-356. Palmer, D.K., O Day, K., and Margolis, R.L. (1990) The centromere specific histone CENP-A is selectively retained in discrete foci in mammalian sperm nuclei. Chromosoma 100, 32-36. 

ADP-ribosylation has also been implicated as a proteolytic antagonist during embryonic development [231]. Following fertilization in sea urchin, sperm-specific histones are degraded by the sperm-histone-selective (SpH) protease and subsequently replaced by cleavage stage histone variants. During this process, the maternal replacement histones are protected from proteolysis by ADP-ribosylation. 

Prenatal exposure of rats and rabbits to doses of methylacrylonitrile that did not induce toxicity in the adults also did not induce developmental toxicity in the fetus. Methylacrylonitrile was also determined not to be a selective reproductive toxin. In a continuous breeding study in rats, doses that caused decreases in epididymal sperm density of Fi... 

Selection of male breeders Animals with proven sexual maturity, e.g. presence of sperm in ejaculate, proven fertility. 

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