existence starts during existence ends during skeletal muscle fiber fetal and neonatal skeletal muscle fiber 2022-02-21T15:43:16Z A skeletal muscle fiber found at the fetal and neonatal stages. In mammalian fetuses and neonates, skeletal muscle expresses myosin heavy chain-neonatal (MyHC-neo, encoded by the MYH8 gene). This expression disappears shortly after birth and is replaced by expression of adult heavy chain myosins. post-embryonic stage neonate stage Paola Roncaglia