Embryonic nuclei

The dynamic picture of a vapor at a pressure near is then somewhat as follows. If P is less than P , then AG for a cluster increases steadily with size, and although in principle all sizes would exist, all but the smallest would be very rare, and their numbers would be subject to random fluctuations. Similarly, there will be fluctuations in the number of embryonic nuclei of size less than rc, in the case of P greater than P . Once a nucleus reaches the critical dimension, however, a favorable fluctuation will cause it to grow indefinitely. The experimental maximum supersaturation pressure is such that a large traffic of nuclei moving past the critical size develops with the result that a fog of liquid droplets is produced. 

King, T., and R. Briggs, Serial transplantation of embryonic nuclei. Cold Spring Harb. Symp. Quant. Biol. 21 271-290, 1956. 

In systems displaying polymorphism, embryonic nuclei with structures resembling each of the mature phases may be present. The appearance of polymorphs is then kinetically controlled by the relative rates of nucleation and crystal growth of the different polymorphs [64]. The presence of impurities may lead to the formation of a particular polymorph by either... 

Barrier to nudeation. Embryonic nuclei with rfree energy by melting hence are not viable. Nudei with r > rcriscai decrease their free energy by growing hence become stable. 

In the absence of any nudeation site, homogeneous nudeation will eventually occur as the atoms cluster together to form embryonic nuclei. There is a critical radius for these... 

Staining with chromosomes of embryonic nuclei with DAPI Protocol 7... 

From Equation 11.9, for an embryonic nucleus of radius r to coexist with its melt, the melt must be undercooled by an amount equal to ATm- Or the critical size for a viable nucleus for a given imdercooling is given by... 

The peak AG at critical is the barrier to nucleation. An embryonic nucleus with r < r mcai can reduce its free energy by dissolving, hence it is not viable. On the other hand, if r > r nticau the embryonic nucleus can reduce its free energy by growing and becomes a stable nucleus. Differentiating Equation 11.11 with respect to r to find yields... 

The very beginning of the first mitotic cell cycle of the mouse embryo seems to be controlled by the mechanisms characteristic for both meiotic and mitotic cell cycles. Active MAP kinase, its substrate p90rsk and the CSF activity itself could influence the cellular processes within the one-cell embryo. Indeed, we have observed that despite the entry into the interphase (as judged by the low activity of MPF) some proteins are actively phosphorylated as during the meiotic M phase (e.g. 35 kDa complex Howlett et al 1986, Szollosi et al 1993), the nuclei and the microtubule interphase network start to form only 1.5 hours after activation (Szollosi et al 1993). This delay in the phenomena characteristic for the interphase could be linked to the mixed meiotic/mitotic character of this early period. This delay probably allows the correct transformation of the sperm nucleus into the male pronucleus. In species like Xenopus or Drosophila the transitional period between the meiotic and the mitotic cell cycle control is probably much shorter since it is proportional to duration of the short first cell cycle of these rapidly cleaving embryos. Mammalian embryos are perhaps the most suitable to study this transition because of the exceptionally long first embryonic cell cycle. 

The entry into the first mitotic M phase at the end of the first embryonic cell cycle requires activation of MPF. In the mouse one-cell embryo this activation is fully autonomous from the nucleus (Ciemerych 1995, Ciemerych et al 1998). It proceeds within the cytoplasts obtained either by enucleation or by bisection of the embryo. Other autonomous phenomena are the cortical activity, or the deformation of the one-cell embryo, directly preceding the entry into first mitosis (Waksmundzka et al 1984) and the cyclic activity of K+ ion channels (Day et al 1998). The role of the cortical activity remains unknown however, the fact that it directly precedes the entry into the first mitotic M phase suggests that it could be linked to the activation... 

Korean scientists report human embryonic stem cell produced using a nucleus from an adult cell... 

Starting in 1993, reports have appeared that in rat striatum and nucleus accum-bens D2-like autoreceptors, when activated, enhanced removal of dopamine from the extracellular space by means of the dopamine transporter (DAT) as studied by voltammetry (Table2). D2 receptor activation also increased [3H]-dopamine uptake in Xenopus oocytes transfected with both the human D2 receptor and the human DAT (Mayfield and Zahniser 2001), as well as the uptake of a fluorescent DAT substrate in human embryonic kidney cells equally transfected with both the human D2 receptor and the human DAT (Bolan et al. 2007). In accord with this autoreceptor-transporter connection, clearence of dopamine from the striatal extracellular space in vivo was reduced in D2 receptor knockout mice (Dickinson et al. 1999). Unfortunately, however, the data in the literature are by no means consistent. No effect of D2 receptor activation on the DAT was observed in another rat striatum study (Prasad and Amara 2001), in synaptosomes from rat and human neocortex (Feuer-stein, unpublished observations), and in PC 12 cells that possess D2 receptors and the DAT (Pothos et al. 1998). In a second study with D2 receptor knockout mice, uptake of dopamine in the striatum was increased rather than decreased (Schmitz et al. 2002). The reason for these discrepancies is not clear. It has been suggested that the clearance measurements by means of voltammetry were not appropriate for assessment of the function of the DAT (Prasad and Amara 2001). 

Human embryonic stem cells (hESCs) were first derived from the inner cell mass (ICM) from the blastocyst stage (-100-200 cells) of embryos generated by in vitro fertilization [35,36]. In humans the blastocyst is an early-stage embryo, approximately 4 to 5 days old. The blastocyst can be formed by means of either in vitro fertilization or somatic cell nuclear transfer, in which the nucleus of a somatic cell is combined with an enucleated oocyte. Methods have been developed to derive hESCs from the late morula stage (30-40 cells) and from arrested embryos (16-24 cells incapable of further development), and more recently from single blastomeres isolated from 8-cell embryos (37). 

OH)2D3-mediated phosphorylation [67]. In the case of PKC, 1,25-(OH)2D3 causes translocation of PKC-/ to the plasma membrane and PKC-a to the nucleus [269-271], Both PKC iso types are calcium-dependent, and l,25-(OH)2D3 does not affect the calcium-independent PKC-f [271], Brown and DeLuca [272] demonstrated that VDR phosphorylation is rapid, occurring within 1 h following treatment of l,25-(OH)2D3 of embryonic chick duodenal organ culture. In addition, phosphorylation occurred before calcium uptake and the 1,25-(OH)2D3-dependent increase in calcium-binding protein mRNA. Proteolytic digestion of the l,25-(OH)2D3-dependent phosphorylation of porcine VDR was mapped and shown to be localized to a 23 Kd fragment of the C-terminal domain [273]. 

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