328
Xenopus
FIGURE 23.1 Schematic of the different methods used for nuclear reprogramming. (Clockwise from top left) Somatic cell nuclear
transfer/egg-NT: Nucleus of a somatic cell is isolated and transferred to an enucleated egg; the formed zygote then can develop into a
cloned organism. Transcription factor-mediated reprogramming: Cultured cells are induced to pluripotency by overexpression of indicated transcription factors. Cell fusion: Somatic cells are fused with embryonic stem cells. The embryonic components of the ES cell
induce reprogramming of the differentiated cell. Extract treatment: Somatic cell nuclei are introduced to Xenopus egg extracts, which
induce their reprogramming. Oocyte-NT: Multiple somatic cell nuclei are transplanted into the germinal vesicle (nucleus) of an oocyte.
Oocyte factors reprogram the nuclei.
too long before NT was proven possible on mammalian
systems, another prominent study published for the f rst
time the establishment of progressively growing cultures
of pluripotent embryonic cells derived from mice ( Evans
and Kaufman, 1981 ). Another breakthrough followed
almost two decades later, with the establishment of human
embryonic stem cell lines ( Thomson et al., 1998 ). These
studies opened up the possibility of isolating embryonic
cells from cloned embryos for clinical applications. In
conjunction with one another, both these techniques can
have far-reaching effects on therapeutical cloning and
human disease modeling.
23.3.2. USE OF ALTERNATIVE METHODS FOR
NUCLEAR REPROGRAMMING
As the popularity of the initial SCNT results grew, other
techniques for reprogramming cells to pluripotency emerged
( Figure 23.1 ). Reprogramming by cell fusion, for example,
functions through the fusion of plasma membranes of an
ES-cell with a differentiated cell type ( Figure 23.1 ; Blau et al.,
1983 ). In the resulting fused cell, the differentiated nucleus
is exposed to embryonic components of the ES cell, leading
to expression of stem cell-specifc genes, and is thus reprogrammed. The beginning of the 21st century witnessed another
Xenopus
FIGURE 23.1 Schematic of the different methods used for nuclear reprogramming. (Clockwise from top left) Somatic cell nuclear
transfer/egg-NT: Nucleus of a somatic cell is isolated and transferred to an enucleated egg; the formed zygote then can develop into a
cloned organism. Transcription factor-mediated reprogramming: Cultured cells are induced to pluripotency by overexpression of indicated transcription factors. Cell fusion: Somatic cells are fused with embryonic stem cells. The embryonic components of the ES cell
induce reprogramming of the differentiated cell. Extract treatment: Somatic cell nuclei are introduced to Xenopus egg extracts, which
induce their reprogramming. Oocyte-NT: Multiple somatic cell nuclei are transplanted into the germinal vesicle (nucleus) of an oocyte.
Oocyte factors reprogram the nuclei.
too long before NT was proven possible on mammalian
systems, another prominent study published for the f rst
time the establishment of progressively growing cultures
of pluripotent embryonic cells derived from mice ( Evans
and Kaufman, 1981 ). Another breakthrough followed
almost two decades later, with the establishment of human
embryonic stem cell lines ( Thomson et al., 1998 ). These
studies opened up the possibility of isolating embryonic
cells from cloned embryos for clinical applications. In
conjunction with one another, both these techniques can
have far-reaching effects on therapeutical cloning and
human disease modeling.
23.3.2. USE OF ALTERNATIVE METHODS FOR
NUCLEAR REPROGRAMMING
As the popularity of the initial SCNT results grew, other
techniques for reprogramming cells to pluripotency emerged
( Figure 23.1 ). Reprogramming by cell fusion, for example,
functions through the fusion of plasma membranes of an
ES-cell with a differentiated cell type ( Figure 23.1 ; Blau et al.,
1983 ). In the resulting fused cell, the differentiated nucleus
is exposed to embryonic components of the ES cell, leading
to expression of stem cell-specifc genes, and is thus reprogrammed. The beginning of the 21st century witnessed another