PURPOSE: To examine the distribution and timing of expression of nonmuscle myosin IIB (nmMyH IIB) and the extraocular muscle (EOM)-specific myosin (EO- @entity29111 ) during postnatal development of the @entity35 extraocular muscles. METHODS: Whole orbits were collected from postnatal development day (P) 1 through P30 from @entity35 . Samples were analyzed by immunofluorescence microscopy and Western blot to examine the distribution and abundance of nmMyH IIB and EO- @entity29111 compared with other myosin isoforms and sarcomeric a-actinin. Polyclonal antibodies were produced to specifically detect EO- @entity29111 . Postnatal limb muscles were used as control. RESULTS: Analysis of EOM morphology in the developing orbits indicates that the global and orbital layers are not evident until day @entity22163 . The distribution of nmMyH IIB changes between days P10 and @entity22163 from a subsarcolemma distribution to an intrafiber distribution in the global layer. EO- @entity29111 appears by day @entity22163 , primarily in the orbital layer of the EOMs. Sarcomeric a-actinin was equally abundant in the EOMs at all stages. Fetal @entity29111 was the predominant isoform at day P1 but slowly diminished in abundance with age in a layer-specific manner. CONCLUSIONS: These data demonstrate that significant changes occur in the EOMs from P10 to @entity22163 and suggest that visual stimulation may play a role in the signals that regulate both nmMyH IIB and EO- @entity29111 developmental transitions. The pronounced distinctions of the orbital and global layers occurring by @entity22163 establish the adult morphologic phenotype of the muscle.

Postnatal changes in the developing XXXX extraocular muscles.

@entity29111 :: ('29605(Tax:10116)', 'Gene') :: ['MyHC'] @entity22163 :: ('25164(Tax:10116)', 'Gene') :: ['p15', 'P15'] @entity35 :: ('10116', 'Species') :: ['rat', 'Sprague-Dawley rats']
@entity35 :: (10116,Species) :: ['rat']
