Enhancement of extra chromosomal recombination in somatic cells by affecting the ratio of homologous recombination (HR) to non-homologous end joining (NHEJ)

Advancements in somatic cell gene targeting have been slow due to the finite lifespan of somatic cells and the overall inefficiency of homologous recombination. The rate of homologous recombination is determined by mechanisms of DNA repair, and by the balance between homologous recombination (HR) and non-homologous end joining (NHEJ). A plasmid-to-plasmid, extra chromosomal recombination system was used to study the effects of the manipulation of molecules involved in NHEJ (Mre11, Ku70/80, and p53) on HR/NHEJ ratios. In addition, the effect of telomerase expression, cell synchrony, and DNA nuclear delivery was examined. While a mutant Mre11 and an anti-Ku aptamer did not significantly affect the rate of NHEJ or HR, transient expression of a p53 mutant increased overall HR/NHEJ by 2.5 fold. However, expression of the mutant p53 resulted in increased aneuploidy of the cultured cells. Additionally, we found no relationship between telomerase expression and changes in HR/NHEJ. In contrast, cell synchrony by thymidine incorporation did not induce chromosomal abnormalities, and increased the ratio of HR/NHEJ 5-fold by reducing the overall rate of NHEJ. Overall our results show that attempts at reducing NHEJ by use of Mre11 or anti-Ku aptamers were unsuccessful. Cell synchrony via thymidine incorporation, however, does increase the ratio of HR/NHEJ and this indicates that this approach may be of use to facilitate targeting in somatic cells by reducing the numbers of colonies that need to be analyzed before a HR is identified.

A highly efficient method for porcine cloning by nuclear transfer using in vitro-matured oocytes

To date, the efficiency of pig cloning by nuclear transfer of somatic cell nuclei has been extremely low, with less than 1% of transferred embryos surviving to term. Even the utilization of complex procedures such as two rounds of nuclear transfer has not resulted in greater overall efficiencies. As a result, the applicability of the technology for the generation of transgenic and cloned animals has not moved forward rapidly. We report here a simple nuclear transfer protocol, utilizing commercially available in vitro-matured oocytes, that results in greater than 5% overall cloning efficiency. Of five recipients receiving nuclear transfer embryos produced with a fetal fibroblast cell line as nuclear donor, all five established pregnancies by day 28 (100%), and 4/5 (80%) went to term. Efficiencies for each transfer were 7% (9 piglets/128 doublets transferred), 5% (5/100), 12% (7/59), and 6.6% (7/106). The overall efficiency in all recipients was 5.5% and in pregnant recipients 7.7%, with a total of 28 cloned piglets produced. With the average fusion rate being 58%, the percentage of fused doublets producing a live piglet approached 12%. The method described here can be undertaken by a single micromanipulator at a reasonable cost, and should facilitate the broad utilization of porcine cloning technology in transgenic and nontransgenic applications.

Expression of connexin 43 mRNA and protein in developing follicles of prepubertal porcine ovaries

A major form of cell-cell communication is mediated by gap junctions, aggregations of intercellular channels composed of connexins (Cxs), which are responsible for exchange of low molecular weight (<1200 Da) cytosolic materials. These channels are a growing family of related proteins. This study was designed to determine the ontogeny of connexin 43 (Cx43) during early stages of follicular development in prepubertal porcine ovaries. A partial-length (412 base) cDNA clone was obtained from mature porcine ovaries and determined to have 98% identity with published porcine Cx43. Northern blot analysis demonstrated a 4.3-kb mRNA in total RNA isolated from prepubertal and adult porcine ovaries. In-situ hybridization revealed that Cx43 mRNA was detectable in granulosa cells of primary follicles but undetectable in dormant primordial follicles. The intensity of the signal increased with follicular growth and was greatest in the large antral follicles. Immunohistochemical evaluation indicated that Cx43 protein expression correlated with the presence of Cx43 mRNA. These results indicate that substantial amounts of Cx43 are first expressed in granulosa cells following activation of follicular development and that this expression increases throughout follicular growth and maturation. These findings suggest an association between the enhancement of intercellular gap-junctional communication and onset of follicular growth.

Protein kinase C isoform expression and activity alter paclitaxel resistance in vitro

OBJECTIVE

The aim of this study was to assess the relationship of protein kinase C (PKC) isoform expression and functional activity to the development of multidrug resistance in gynecologic malignancies.

METHODS

Paclitaxel-resistant subclones (T30 and T30-Res) of the Mes-sa human uterine sarcoma cell line were selected through exposure to paclitaxel in vitro. Indices of relative drug resistance were determined by the MTT (3-[4,5-dimethyl-2-thiazolyl]-2, 5-diphenyl-2H-tetrazolium bromide) assay. Differences in the expression pattern of PKC isoforms were assessed by Western blot of cell lysates. Finally, the influence of PKC activity (i.e., translocation to the plasma membrane, confirmed by Western blot of plasma membrane bound protein) on resistance to paclitaxel was examined with the MTT assay in cells preincubated with PMA.

RESULTS

The indices of relative paclitaxel resistance of Mes-sa, Mes-sa-T30, and Mes-sa-T30-Res were 1-, 5-, and 11-fold, respectively. Five (alpha, gamma, iota, lambda, and mu) of the 11 known PKC isoforms were detected in all cell lysates. Only PKC-alpha and PKC-gamma expression increased with increasing indices of paclitaxel resistance. Interestingly, PMA induction of PKC activity reversed resistance to paclitaxel in all cell lines by 2- to 3-fold, and this reversal of drug resistance was associated with a time-dependent translocation of PKC-alpha and PKC-gamma to the plasma membrane compartment.

CONCLUSIONS

Increased expression of only the PKC-alpha and PKC-gamma isoforms correlates with increasing levels of paclitaxel resistance in Mes-sa cells in this in vitro experimental model. However, increased functional activity of these and other PKC isoforms leads to reversal in paclitaxel resistance. Therefore, PKC activating mechanisms normally present in primary tumor cells may be compromised in drug-resistant clones.

Hormonal profiles of callipyge and normal sheep

Five sheep expressing the callipyge gene, which causes muscle hypertrophy, were compared with five normal sheep to determine whether endocrine differences existed between genotypes. Blood samples were taken at 15-min intervals for 6 h to measure serum concentrations of growth hormone and insulin. Thyroxine and IGF-I levels were determined in single samples. No differences were found in mean serum growth hormone concentrations, growth hormone pulse amplitude, or pulse frequency (P > .3). Insulin concentrations were not different between genotypes before or after feeding (4.5 +/- 1.3 ng/mL callipyge vs 4.9 +/- 1.7 ng/mL normal, P > .4). The IGF-I concentrations did not differ (273.8 +/- 17.6 ng/mL callipyge vs 261.4 +/- 12.3 ng/mL normal). Serum thyroxine concentrations also were not different (5.9 +/- 2.3 microg/mL for callipyge vs 5.1 +/- 2.1 microg/mL normal, P > .3). In a separate experiment, five ewe lambs with and five without the callipyge gene were stressed to determine whether the adrenocortical response to stress differed between genotypes. Blood samples were taken at 15-min intervals for 2 h before, during, and after restraint stress. Restraint increased serum cortisol concentrations in both groups (P < .001), but genotypes did not differ at any time (P > .3). These results suggest that differences in muscling are not due to differences in systemic hormone secretion. The results of the second experiment indicate that callipyge and normal sheep have similar adrenocortical responses to stress.