Acetylcholinesterase activity in the myotome of the early chick embryo

Abstract

The myotome of early chick embryos was investigated histochemically by means of the acetylcholinesterase (AChE) reaction. Light-microscopically, at the cervical level, the myotome was first recognized and AChE activity demonstrated at stage 13 (2-day-old embryo). Subsequently, the myotome elongated ventro-laterally along the inner surface of the dermomyotome and reached the ventro-lateral end of the dermomyotome at stage 17 to 18 (3 day-old embryo). AChE activity in the myotome showed subsequent increase in intensity during the course of development. The myotome consisted mainly of AChE-positive cells displaying enzymatic activity along the nuclear membrane and within the cytoplasm. In contrast, almost all cells of the dermomyotome and the interstitial cells were AChE-negative. Electron-microscopically, the myotome cells of the 2 day-old embryo and the cells in the dorso-medial portion of the myotome of the 3 day-old embryo were morphologically undifferentiated; AChE activity was detected in the nuclear envelope and in single short profiles of the endoplasmic reticulum (ER). On the other hand, in the 3 day-old embryo the cells in the ventro-lateral portion of the myotome showed AChE activity in the nuclear envelope, numerous profiles of the ER and some Golgi complexes. These AChE-positive cells were regarded as developing myogenic cells based on their morphological characteristics. The present findings indicate (i) that the appearance of AChE activity in the cytoplasm is the first sign of the differentiation of myogenic cells, and (ii) that in these myogenic cells the increase in AChE activity is based on the development of the ER.

Origin of myotome cells in the chick embryo studied by 3H-thymidine autoradiography and acetylcholinesterase histochemistry.

“…In the present study as well as in the previous study (18), the AChE-positive cells first appeared in the dorso-medial angle of the dermomyotome. The myotome, which consisted of many ACNE-positive and some ACNE-negative cells, elongated ventro-laterally along the inner surface of the dermomyotome, as the development progressed.…”

“…These findings indicate that the AChE-negative cells in the myotome incorporate 3H-thymidine for DNA-synthesis. In addition, the dermomyotome cells are attached by terminal bars at their inner ends (18,26), and cells migrating from the dermomyotome into the myotome were rarely seen in our material or in that of Christ et at. (4) .…”

“…Previously, using 3H-a-BGT autoradiography and ACNE histochemistry on the same sections, we found that the specific labeling of a-BGT was restricted to the ACNE-positive myotome cells, but no sclerotome (mesenchyme) cells were specifically labeled with a-BGT (19). We also reported that almost all cells in the sclerotome including the cells bordering the inner surface of the myotome were ACNE-negative and morphologically undifferentiated (18). These findings do not support the opinion of Meiniel and Bourgeois (15).…”

“…Our study, using the histochemical technique, has revealed that the myotome of the early chick embryo consists mainly of AChE-positive cells displaying enzymatic activity along the nuclear membrane and within the cytoplasm (18). Some AChEnegative cells were also noted throughout the myotome.…”

“…Fluck and Strohman (7) stated that ACNE appears in mononucleated myogenic cells after DNA-synthesis has ceased and before fusion of the mononucleated cells has begun. Previously, we have reported that the ACNE-positive cells in the myotome can be regarded as developing myogenic cells and ACNE-negative cells, as undifferentiated cells, based on their morphological characteristics (18) . All these previous findings taken together suggest that the ACNE-positive myotome cells are no longer capable of proliferation, and also that some of the ACNE-positive myotome cells may be derived from the ACNE-negative myotome cells.…”