The invention provides isolated nucleic acid molecules, designated PGC-1b and PGC-1c nucleic acid molecules, which encode novel isoforms of PGC-1 family members. The invention also provides antisense nucleic acid molecules, recombinant expression vectors containing PGC-1 nucleic acid molecules, host cells into which the expression vectors have been introduced, and nonhuman transgenic animals in which a PGC-1 gene has been introduced or disrupted. The invention still further provides isolated PGC-1 proteins, fusion proteins, antigenic peptides and anti-PGC-1 antibodies. Diagnostic methods utilizing compositions of the invention are also provided.