Transcriptome analysis of two bovine muscles during ontogenesis.

Macro-arrays, on which 1339 human skeletal muscle cDNA clone inserts had been spotted as PCR products, were used to make large-scale measurement of gene expression in bovine muscles during ontogenesis. Ten complex cDNA targets derived from two mixed muscle samples, Rectus abdominis (rather red oxidative muscle, RA) and Semitendinosus (rather white glycolytic muscle, ST), were taken from foetuses at 4 different stages (110, 180, 210, and 260 days post-conception) and from 15-month-old young bulls to generate differential expression patterns. Each sample analysed was prepared from a pool of RNA extracted from muscle tissues sampled from at least 6 different animals. Approximately 200 expression signals were validated and taken into account to provide a first "bovine" muscle gene repertoire. Despite the relatively small number of probes and the heterologous approach, this made it possible to identify up to 7 genes differentially expressed between RA and ST, depending on age. From 110 days post-conception to 15 months of age, differences in the expression levels of 110 genes were detected in the four comparisons between two consecutive ages. By comparing 260 days post-conception foetal muscles and adult muscles, up to 87 genes were overexpressed, whereas only 7 genes were shown to be down-regulated. Among these genes, 33% have unknown biological functions. Taken together, the results reported here underline the importance of the last three months of gestation in muscle myogenesis, and highlight new genes involved in this process.