OBJECTIVE To produce a clonal equine myoblast cell line that retains the ability to divide for multiple passages and differentiate into multinucleated myotubes during specific conditions. SAMPLE Cultured primary equine skeletal muscle-derived cells from a healthy Thoroughbred. PROCEDURES Cell cultures were transfected by electroporation with a plasmid (pNIT) that expresses the temperature-sensitive simian vacuolating virus 40 large T antigen (TAg), which can be controlled by a doxycycline-responsive promoter. Cells that stably integrated the TAg were selected and expanded to passage 25. For each passage, differentiation and fusion properties of the cells were determined and immunocytochemical analyses were performed to evaluate expression of TAg and other muscle-specific proteins. Optimum conditions that led to cell differentiation into myotubes were also determined. RESULTS Compared with nontransfected control cells, myogenic, desmin-positive cells expressed the TAg when incubated at 33°C and could be maintained in culture for numerous passages. Reduced expression of TAg was identified in cells incubated at 37°C or when incubated with doxycycline at 33°C. Expression of TAg was not detected when cells were incubated with doxycycline at 37°C, and when serum was withdrawn from the culture medium, those clones differentiated into a pure population of multinucleated myotubes. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that production of an immortalized clonal equine skeletal muscle cell line was possible. A clonal equine skeletal muscle cell line will be a valuable in vitro tool for use in equine physiology and disease research.

Objective: To determine whether a novel optimized plasmid carrying the porcine growth hormone–releasing hormone (GHRH) wild-type cDNA administered at a lower dose was as effective at eliciting physiologic responses as a commercial GHRH plasmid approved for use in Australia. Animals: 134 gilts. Procedures: Estrus was synchronized and gilts were bred. Pregnant gilts were assigned to 2 treatment groups (40 gilts/group) or 1 untreated control group (24 gilts). Gilts in one of the treatment groups received the commercial GHRH plasmid, whereas gilts in the other treatment group received a novel optimized GHRH plasmid; both plasmids were administered IM in the right hind limb, which was followed by electroporation. Sow and litter performance were monitored for the 3 gestations after treatment. Results: A significant increase in insulin-like growth factor-I concentrations, decrease in perinatal mortality rate, increase in the number of pigs born alive, and increase in the weight and number of pigs weaned were detected for both groups receiving the GHRH-expressing plasmids, compared with values for the control group. Additionally, there was a significant decrease in sow attrition in GHRH-treated females, compared with attrition in the control group, during the 3 gestations after treatment. Conclusions and Clinical Relevance: Both of the GHRH plasmids provided significant benefits for sow performance and baby pig survivability for pregnant and lactating sows and their offspring during the 3 gestations after treatment, compared with results for untreated control gilts. Use of a novel optimized plasmid reduced the effective plasmid dose in these large mammals.

Corynebacterium pseudotuberculosis was transformed by electroporation, using pNG2, an erythromycin-resistance plasmid from C diphtheriae. Corynebacterium pseudotuberculosis cultivated in brain-heart infusion broth was washed 3 times with water, and resuspended to a final concentration of about 5 X 10(13) colony-forming units/ml. An electroporator constructed in our laboratory incorporated an electrode with 0.8-mm interelectrode gap, using disposable spectrophotometer cuvettes as containers for electroporation. The pNG2 was prepared in Escherichia coli and 4 to 16 microgram of pNG2 DNA was mixed with 400-microliter amounts of cell suspension in prechilled cuvettes. After incubation on ice for 5 to 10 minutes, the mixture was electroporated at field strengths of up to 18 kV/cm, mixed with 1.5 ml of brain-heart infusion broth, and incubated at 37 C for 2 hours with agitation. Aliquots were then plated on brain-heart infusion blood agar with 15 microgram of erythromycin/ml. Corynebacterium pseudotuberculosis was transformed at a maximal efficiency of approximately 4 X 10(4) transformants/microgram of pNG2 DNA. Most total transformants and most transformants per microgram of pNG2 were generated at a field strength of 18 kV/cm. When the concentration of pNG2 DNA was varied, the average total number of transformants increased through a concentration of 30 microgram/ml, but the efficiency of transformation was highest at the lowest DNA concentration. Transformants contained unmodified pNG2.