The M-line and its associated @entity908 kinase (CK) M-isoform ( @entity36651 ) are ubiquitous features of skeletal and cardiac muscle. The M-line maintains myosin myofilaments in register, links the contractile apparatus to the cytoskeleton for external force transfer and localizes CK-based energy storage and transfer to the site of highest @entity855 demand. We establish here that the muscle group responsible for movements of the eye, extraocular muscle (EOM), is divergent from other striated muscles in lacking both an M-line and its associated @entity36651 . Although an M-line forms during myogenesis, both in vivo and in vitro, it is actively repressed after birth. Transcripts of the major M-line structural proteins, @entity69440 and @entity29946 , follow the same pattern of postnatal downregulation, while the embryonic heart-specific EH- @entity69440 transcript is expressed early and retained in adult eye muscle. By immunocytochemistry, myomesin protein is absent from adult EOM sarcomeres. M-line suppression does not occur in organotypic co-culture with oculomotor motoneurons, suggesting that the mechanism for suppression may lie in muscle group-specific activation or workload patterns experienced only in vivo. The M-line is, however, still lost in dark-reared @entity35 , despite the developmental delay this paradigm produces in the visuomotor system and EOMs. EOM was low in all CK isoform transcripts except for the sarcomeric mitochondrial ( @entity61823 ) isoform. Total CK enzyme activity of EOM was one-third that of hindlimb muscle. These findings are singularly unique among fast-twitch skeletal muscles. Since EOM exhibits isoform diversity for other sarcomeric proteins, the M-line/ @entity36651 divergence probably represents a key physiological adaptation for the unique energetics and functional demands placed on this muscle group in @entity1319 .

Postnatal suppression of myomesin, muscle @entity908 kinase and the M-line in XXXX extraocular muscle.

@entity908 :: ('MESH:D003401', 'Chemical') :: ['creatine'] @entity1319 :: ('MESH:D015835', 'Disease') :: ['voluntary and reflexive eye movements'] @entity29946 :: ('306616(Tax:10116)', 'Gene') :: ['myomesin 2'] @entity36651 :: ('24265(Tax:10116)', 'Gene') :: ['CK-M'] @entity61823 :: ('688698(Tax:10116)', 'Gene') :: ['Ckmt2'] @entity35 :: ('10116', 'Species') :: ['rats'] @entity69440 :: ('316740(Tax:10116)', 'Gene') :: ['myomesin 1'] @entity855 :: ('MESH:D000255', 'Chemical') :: ['ATP']
@entity35 :: (10116,Species) :: ['rat']
