Transgenic pigs are promising donor organisms for xenotransplantation as they share many anatomical and physiological characteristics with humans. Recently, a step has been moved closer to xenotransplantation by producing genetically modified pigs that has no α-1,3-Gal epitope, the major xenoantigens triggering HAR of pig to primate xenografts. Further genetic modifications such as expression of human complementary regulatory proteins, CD39, endothelial protein C receptor, heme-oxygenase 1, thrombomodulin, tissue factor pathway inhibitoras well as modulators of the HLA-E/β-2-microglobulin, and CTLA-4Ig are due to address for further rejection mechanisms and incompatibilities between porcine and primate blood coagulation systems. Although the pig is the favored species for use as a xenograft donor, a detailed description of the transgenic pig development and surgical technique is lacking which seems mandatory to address for broader understanding of this issue.

Several vertebrate species are able to epimorphically regenerate tissue of appendages or whole appendages such as fingertips, limbs, fins, tails, antlers, and ear tissue via the formation of a blastema of proliferating cells. For structure such as mammalian ear tissue and fingertips and antlers, the origin of the cells for regeneration is uncertain, but in others, such as fish fin regeneration and amphibian limb and tail regeneration, studies revealed that the blastema is formed by the dedifferentiation of mature cells local to the region of injury. Moreover, regeneration requires specification of the identity of new tissues to be made either in lower or higher vertebrates. Whether this process relies only on intrinsic regulative properties of regenerating tissues or whether wound signaling provides input into tissue repatterning is not known. In this review, authors have made efforts to put emphasis on signaling events, importance of polarity during regeneration and put forth how the limitations of regeneration could be overcome in higher vertebrates such as animals and humans.

Embryonic stem (ES) cells are pluripotent cells derived from the inner cell mass cells of blastocyst with the potential to maintain an undifferentiated state indefinitely. Fully characterized ES cell lines express typical stem cell markers, possess high levels of telomerase activity, show normal karyotype and have the potential to differentiate into numerous cell types under in vitro and in vivo conditions. Therefore, ES cells are potentially valuable for the development of cell transplantation therapies for the treatment of various diseases in animals as well as in humans. However, important problems associated with ES cells from in vitro fertilized blastocysts particularly from humans must be resolved before taking up its therapeutic applications. Current techniques for directed differentiation into somatic cell populations remain inefficient and yield heterogeneous cell populations. This review therefore focuses on ES cells with respect to in vitro propagation and differentiation in basic cell and developmental biology for successful use of these cells in therapeutics.