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However, 42 H. de Mello Brandão et al. Fig. 3 The fluorescence of bovine fibroblast cells successfully transfected with GFP gene: a MWCNT-COOH with GFP gene; b poly(ethyleneimine) with GFP gene [99] the amount of gene or protein conjugated by MWCNT-CHOO is still limited, resulting in low transfection efficiency (Fig. 3a) when compared to the reagent poly (ethyleneimine) (Fig. 3b). 2 Contribution of CNTs to Conventional Techniques In somatic cells, embryonic-stem cells or in sperm-mediated gene transfer, several methods have been developed for the establishment of an efficient gene delivery system, such as viral vectors [100–102] or nonviral ones, like liposomes [5, 103], physical or chemical methods [104–106].

Both male and female pronuclei are directed to the center of the zygote where they merge, initiating the process of parental gene transcription (paternal and maternal) and cleavage. After the sixteen-cell stage, the embryo is called a morula (Fig. 1a), Fig. 1 a Micrography of bovine morula. b Atomic Force image of bovine Zona Pellucida (supported by Bernardes-Filho R). c Micrography of bovine blastocyst. * Embryoblast and ** blastocoele 34 H. de Mello Brandão et al. and when the blastocoele begins to take form it is given the name of blastocyst.

During the follicular growth, the oocyte meiosis remains at rest (dictyate nucleus), being normally re-established with the extrusion of the first polar corpuscle (the moment of occurrence varies depending on the species) and their ovulation, when the oocyte maturation continues [14–16]. The oocyte maturation and the meiosis are only concluded with the fertilization process, when the oocyte becomes a zygote. In order for the sperm fertilization to occur, it must firstly be able to transpose the ZP (aided by enzymes present in its acrosome) and merge with the plasma membrane of the oocyte.