Fructose metabolism in the adult mouse optic nerve, a central white matter tract.

Our recent report that fructose supported the metabolism of some, but not all axons, in the adult mouse optic nerve prompted us to investigate in detail fructose metabolism in this tissue, a typical central white matter tract, as these data imply efficient fructose metabolism in the central nervous system (CNS). In artificial cerebrospinal fluid containing 10 mmol/L glucose or 20 mmol/L fructose, the stimulus-evoked compound action potential (CAP) recorded from the optic nerve consisted of three stable peaks. Replacing 10 mmol/L glucose with 10 mmol/L fructose, however, caused delayed loss of the 1st CAP peak (the 2nd and 3rd CAP peaks were unaffected). Glycogen-derived metabolic substrate(s) temporarily sustained the 1st CAP peak in 10 mmol/L fructose, as depletion of tissue glycogen by a prior period of aglycaemia or high-frequency CAP discharge rendered fructose incapable of supporting the 1st CAP peak. Enzyme assays showed the presence of both hexokinase and fructokinase (both of which can phosphorylate fructose) in the optic nerve. In contrast, only hexokinase was expressed in cerebral cortex. Hexokinase in optic nerve had low affinity and low capacity with fructose as substrate, whereas fructokinase displayed high affinity and high capacity for fructose. These findings suggest an explanation for the curious fact that the fast conducting axons comprising the 1st peak of the CAP are not supported in 10 mmol/L fructose medium; these axons probably do not express fructokinase, a requirement for efficient fructose metabolism.

Proteomic analysis of early reprogramming events in murine somatic cells incubated with Xenopus laevis oocyte extracts demonstrates network associations with induced pluripotency markers.

The reprogramming of somatic cells into a pluripotent/embryonic-like state holds great potential for regenerative medicine, bypassing ethical issues associated with embryonic stem cells (ESCs). Numerous methods, including somatic cell nuclear transfer (SCNT), fusion to pluripotent cells, the use of cell extracts, and expression of transcription factors, have been used to reprogram cells into ES-like cells [termed induced pluripotent stem cells (iPSCs)]. This study investigated early events in the nuclei of permeabilized murine somatic cells incubated in cytoplasmic extract prepared from Xenopus laevis germinal vesicle-stage oocytes by identifying proteins that showed significant quantitative changes using proteomic techniques. A total of 69 protein spots from two-dimensional electrophoresis were identified as being significantly altered in expression after treatment, and 38 proteins were identified by tandem mass spectrometry. Network analysis was used to highlight pathway connections and interactions between these identified proteins, which were found to be involved in many functions--primarily nuclear structure and dynamics, transcription, and translation. The pluripotency markers Klf4, c-Myc, Nanog, and POU5F1 were highlighted by the interaction network analysis, as well as other compounds/proteins known to be repressed in pluripotent cells [e.g., protein kinase C (PRKC)] or enhanced during differentiation of ESCs (e.g., retinoic acid). The network analysis also indicated additional proteins and pathways potentially involved in early reprogramming events.

Reprogramming of ovine somatic cells with Xenopus laevis oocyte extract prior to SCNT improves live birth rate.

The birth of live animals following somatic cell nuclear transfer (SCNT) has demonstrated that oocytes can reprogram the genome of differentiated cells. However, in all species the frequency of development of healthy offspring is low; for example, in sheep, approximately only 5% of blastocysts transferred develop to term, and less than 3% develop to adulthood. Such low efficiencies, coupled with the occurrence of developmental abnormalities, have been attributed to incomplete or incorrect reprogramming. Cytoplasmic extracts from both mammalian and amphibian oocytes can alter the epigenetic state of mammalian somatic nuclei and reprogram gene expression to more resemble that of pluripotent cells. Therefore, it may be possible to increase the frequency or success of normal development by pretreating somatic cells to be used as nuclear donors prior to SCNT. In the present study, permeabilized ovine fetal fibroblasts were pretreated with a cytoplasmic extract produced from germinal vesicle (GV) stage Xenopus laevis oocytes. No increase in the frequency of development to blastocyst stage or pregnancy rate was observed; however, live birth and survival rates were significantly improved. Development to term of blastocysts transferred increased from 3.1% in the control group, to 14.7% in the treated group (a 4.7-fold increase), and even though the subsequent survival of lambs produced from treated cells was reduced by 60%, the percentage of lambs surviving to adulthood of blastocysts transferred (5.9%) increased 1.9-fold compared to controls. This study is the first to report the birth of live offspring and an increase in cloning efficiency, after crossspecies pre-reprogramming using Xenopus GV stage oocyte extract.