Expression of insulin‐like growth factor family members in myostatin null mice (1032.3)

Myostatin inhibits while insulin‐like growth factors (IGF) 1 and 2 increase pre‐ and postnatal skeletal muscle growth. However, the contribution of altered IGF expression to the hypermuscular phenotype of myostatin null (MN) animals is unclear. Wild type (WT) and MN mice were euthanized at approximately 14 days of gestation (‐7d), birth (0d), 7 days (7d), weaning (21d), sexual maturity (42d), and mature size (70d). From fetal mice, RNA was extracted from the entire body. For the neonatal periods, 0d and 7d, all muscles from the hind limbs were compiled for RNA extraction. At 21d, 42d, and 70d, biceps femoris, tibialis anterior, triceps brachii, and gastrocnemious‐soleus complex were collected. As expected, muscle weights increased up to 90% in MN mice compared with WT mice at 21d, 42d and 70d. However, IGF1 expression tended to be decreased by 25 ‐ 50% (P < 0.10) in MN mice compared to WT mice. Additionally, IGF2 expression in MN fetuses tended to be decreased by 30% (P < 0.10) in MN mice compared to WT mice; however IGF2 expression did not differ between genotypes at 0d and 7d. At 21d in biceps femoris muscles, IGF2 expression was increased more than 2 fold (P < 0.01) in MN compared to WT mice. Similarly, at 42d and 70d in biceps femoris muscle, IGF2 expression was increased over 4 fold (P < 0.01) in MN compared to WT mice. Therefore, increased postnatal IGF2 expression may contribute to increased muscle hypertrophy observed in MN mice.