Mascarello F, Rowlerson A M
Istituto di Anatomia degli Animali Domestici con Istologia ed Embriologia, Università di Milano, Italy.
Anat Embryol (Berl). 1992;185(2):143-53. doi: 10.1007/BF00185915.
The late fetal development of rat extra-ocular and masticatory muscles was examined by myosin immunohistochemistry. The pattern of slow and neonatal myosin isoform expression in primary and secondary myotubes in these muscles was generally similar to that seen by others in limb muscles. We observed a consistent difference between the Sprague-Dawley and Wistar rats in the degree of maturity reached by all muscles studied at a particular age. In both strains, extra-ocular muscles were also about one day in advance of the masticatory muscles. Thus, secondary myotubes were first seen at E17 in Wistar extraocular muscles, at E18 in Sprague-Dawley extra-ocular muscles and Wistar masticatory muscles, and at E19 in Sprague-Dawley masticatory muscles. There was a strikingly early and complete type differentiation of primary myotubes in extraocular muscles, and tonic myosin first appeared before birth in presumptive extrafusal tonic fibres in the orbital layer of the oculorotatory muscles. Throughout the late fetal period, retractor bulbi was composed of fast myotubes only, but these myotubes were not arranged in classical clusters. In the masticatory muscles at E17/E18 some slow primary myotubes started to express tonic myosin, and these presumptive spindle bag2 fibres were located only in regions of the muscles known to contain spindles in the adult. Presumptive bag1 fibres appeared about a day later (initially without tonic myosin), and in the region of the spindle cluster in anterior deep masseter extrafusal secondary myotube production appeared to be suppressed.
通过肌球蛋白免疫组织化学检查了大鼠眼外肌和咀嚼肌的晚期胎儿发育情况。这些肌肉中初级和次级肌管中慢肌球蛋白和新生肌球蛋白同工型的表达模式通常与其他人在肢体肌肉中观察到的相似。我们观察到，在特定年龄时，所研究的所有肌肉在成熟程度上，斯普拉格 - 道利大鼠和Wistar大鼠之间存在一致的差异。在这两个品系中，眼外肌的发育也比咀嚼肌提前约一天。因此，在Wistar大鼠的眼外肌中，次级肌管最早在胚胎第17天出现；在斯普拉格 - 道利大鼠的眼外肌和Wistar大鼠的咀嚼肌中，次级肌管最早在胚胎第18天出现；而在斯普拉格 - 道利大鼠的咀嚼肌中，次级肌管最早在胚胎第19天出现。眼外肌中的初级肌管有显著早期且完全的类型分化，强直性肌球蛋白在出生前就首次出现在眼旋转肌眶层的假定梭外强直纤维中。在整个胎儿晚期，眼球退缩肌仅由快肌管组成，但这些肌管并非以经典的簇状排列。在胚胎第17/18天的咀嚼肌中，一些慢初级肌管开始表达强直性肌球蛋白，这些假定的纺锤袋2纤维仅位于成年肌肉中已知含有纺锤体的区域。假定的袋1纤维大约在一天后出现（最初没有强直性肌球蛋白），并且在前深层咬肌的纺锤体簇区域，梭外次级肌管的产生似乎受到抑制。
