|Smith, Timothy - Tim|
Submitted to: Animal Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2003
Publication Date: 12/20/2003
Citation: POTTS, J.K., ECHTERNKAMP, S.E., SMITH, T.P., REECY, J.M. 2003. CHARACTERIZATION OF GENE EXPRESSION IN DOUBLE-MUSCLED AND NORMAL-MUSCLED BOVINE EMBRYOS. ANIMAL GENETICS. v. 34(6). p. 438-444. Interpretive Summary: Myostatin is a negative regulator of skeletal muscle growth during fetal development. Conversely, inactivation of the myostatin gene by various mutations in its DNA coding sequence increases the proliferation of muscle fiber numbers, producing the double-muscling syndrome in cattle. Phenotypic traits of double-muscled cattle include a 30% increase in skeletal muscle mass, an equal reduction in carcass fat, increased carcass retail product yield and increased feed efficiency. However, some negative consequences of double-muscling (e.g., increased incidence of dystocia, decreased female fertility, and lower stress tolerance) have discouraged its adoption into commercial beef production systems. The objective of this research was to elucidate molecular mechanisms and pathways through which myostatin functions by identifying genes that are differentially expressed between double-muscled and normal-muscled bovine embryos shortly after expression of the myostatin gene at approximately day 28 of gestation. This information would enable utilization of the positive characteristics of double-muscled cattle while modifying or reducing some of the adverse characteristics of double muscling. Suppressive subtractive hybridization analysis identified 19 genes that were potentially different in level of expression between double-muscled and normal-muscled embryos at 31 to 33 days of gestation, genes that have biological functions which may be directly involved in the regulation of skeletal muscle development by myostatin. Furthermore, several of the identified genes map to chromosomal regions containing quantitative trait loci known to be linked to variation in the myostatin gene.
Technical Abstract: Myostatin, a member of the transforming growth factor-beta superfamily, is a negative regulator of skeletal muscle growth. Cattle with mutations that inactivate myostatin exhibit a remarkable increase in mass of skeletal muscle, called double muscling, that is accompanied by an equally remarkable decrease in carcass fat. Although a mouse myostatin knockout model produces mice with a 200% increase in skeletal muscle mass, molecular mechanisms whereby myostatin regulates skeletal muscle and fat mass are not fully understood. Suppressive subtractive hybridization was used to identify genes that were differentially expressed between double-muscled and normal-muscled bovine embryos shortly after first expression of myostatin. Embryos were collected at 31 to 33 days of gestation, which are 2 to 4 days after high-level expression of myostatin in the developing bovine embryo. Genetic variation at other loci was minimized by using embryonic samples from related Belgian Blue X Hereford cross dams and by breeding to a single Belgian Blue X MARC III sire. The suppressive subtraction hybridization analysis identified 30 DNA clones that were potentially differentially expressed between the two populations of embryos, of which 19 genes were confirmed by macroarray analysis. Several of these genes have biological functions that indicate they are directly involved in myostatin's regulation of skeletal muscle development. Furthermore, several of these genes map to quantitative trait loci known to interact with variation in the myostatin gene.