Genomic stability and physiological assessments of live offspring sired by a bull clone, Starbuck II.

It appears that overt phenotypic abnormalities observed in some domestic animal clones are not transmitted to their progeny. The current study monitored Holstein heifers sired by a bull clone, Starbuck II, from weaning to puberty. Genomic stability was assessed by telomere length status and chromosomal analysis. Growth parameters, blood profiles, physical exams and reproductive parameters were assessed for 12 months (and compared to age-matched control heifers). Progeny sired by the clone bull did not differ (P>0.05) in weight, length and height compared to controls. However, progeny had lower heart rates (HR) (P=0.009), respiratory rates (RR) (P=0.007) and body temperature (P=0.03). Hematological profiles were within normal ranges and did not differ (P>0.05) between both groups. External and internal genitalia were normal and both groups reached puberty at expected ages. Progeny had two or three ovarian follicular waves per estrous cycle and serum progesterone concentrations were similar (P=0.99) to controls. Telomere lengths of sperm and blood cells from Starbuck II were not different (P>0.05) than those of non-cloned cattle; telomere lengths of progeny were not different (P>0.05) from age-matched controls. In addition, progeny had normal karyotypes in peripheral blood leukocytes compared to controls (89.1% versus 86.3% diploid, respectively). In summary, heifers sired by a bull clone had normal chromosomal stability, growth, physical, hematological and reproductive parameters, compared to normal heifers. Furthermore, they had moderate stress responses to routine handling and restraint.

The impact of chromosomal alteration on embryo development.

Chromosome alterations, such as those affecting telomere erosion, predictably occur with each cell division, others, which involve changes to the expression and replication of the X-chromosome occur at particular stages of development, while those that involve loss or gain of chromosomes occur in a random and so far unpredictable manner. The production of embryos in vitro and by somatic cell nuclear transfer (SCNT) has been associated with altered expression of marker genes on the X-chromosome and an increased incidence of chromosomally abnormal cells during early development. In the case of SCNT embryos chromosome abnormalities may be associated with the nuclear donor cell. Telomere rebuilding subsequent to SCNT appears to vary according to species and type of donor cell used. It is speculated that the rate of telomere erosion and incidence of chromosome abnormalities affects developmental potential of early embryos and may be potential predictors of developmental outcome.