The goal here is to utilize induced pluripotent stem cells (iPSC) derived from the inner cell mass (ICM) of porcine blastocysts to clone genetically modified pigs by nuclear transfer (NT) procedures. In our laboratory, the ICM-derived iPSC so far generated are LIF-dependent, have short cell cycle intervals and resemble mouse embryonic stem cells (ESC). They can survive multiple passages without senescing and are, therefore, suitable for introduction of multiple genetic changes under extended pharmacological selection. As the cells are pluripotent and "undifferentiated", and possibly carry the epigenetic "memory" of the ICM from which they originated, they may be more easily reprogrammed during cloning than other somatic cell types and provide fewer abnormalities in offspring born. Accordingly, these cells are likely to have considerable potential for manipulating porcine genetics and hence be of value to the livestock industry and to the biomedical research in general.
Aim 1 is to establish additional lines of LIF-dependent ICM-derived porcine (p) iPSC (pICM-iPSC) by upregulating human POU5F1 and KLF4 transgenes assembled on "tet-on" bicistronic lentiviral vectors, which offer the advantage of effective transgene silencing or removal, and characterize the resulting lines in further detail. Lines that grow vigorously and demonstrate full in vitro and in vivo (teratoma) criteria for pluripotency will then be tested for their ability to participate in chimera production. Such chimeras may also be valuable as an alternative to cloning for creating genetically modified swine.
Aim 2 is to determine whether or not the various LIF-and FGF2-dependent piPSC at our disposal are superior donors than somatic cells for nuclear transfer.
This aim will also allow us to test if there is any difference between the piPSC representing different classes of pluripotency (LIF-and FGF-dependent) and between the pICM-iPSC and analogous LIF-dependent piPSC reprogrammed from somatic cells. A sub-aim will be to verify if the offspring born to pICM-iPSC show fewer developmental abnormalities compared to the somatic cells by nuclear transfer.
Aim 3 is to establish parameters for efficient gene targeting and transgenesis in pICM-iPSC. Transfection procedures and the effective concentration ranges of selection agents and targeting vectors used to introduce a knockout of one of the alleles of the gene encoding the receptor for low density lipoproteins (LDLR) by homologous recombination will be evaluated.
Aim 4 is to delete both alleles of LDLR and thereby produce a genetically modified pig with potential interest to both agriculture and medicine by NT. Loss of function of LDLR in humans causes hypercholesterolemia, coronary heart disease, and onset of the so-called metabolic syndrome. Pigs lacking one or both copies will provide an alternative model to the mouse for studying responses to diet and drugs in treatment of these conditions. LDLR deficiency and associated hypercholesterolemia are also postulated to protect against Salmonella infections. As the pig is an important reservoir for Salmonella, the LDLR-/- model will have a dual purpose for both agricultural and biomedical applications.
The purpose of this proposal is to utilize lines of induced pluripotent stem cells (iPSC) derived from the inner cell mass (ICM) of porcine blastocysts to produce genetically modified pigs by nuclear transfer, i.e. cloning, procedures. Accordingly, these cells are likely to have considerable potential for manipulating porcine genetics and hence be of value to both the livestock industry and to the biomedical sciences.
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