Immunohistochemical detection of myogenin and p21 in methylcholanthrene-induced mouse rhabdomyosarcomas

Abstract

3-Methylcholanthrene (MC)-induced 10 embryonal (ERSs) and 24 pleomorphic rhabdomyosarcomas (PRSs) of the dermis in mouse were examined immunohistochemically for myogenin, p21 and proliferating cell nuclear antigen (PCNA) nuclear reactivity and myosin reactivity. ERSs had higher expression of myogenin and p21 compared with that of myosin. PRSs were divided into two groups having high (moderate or marked reactivity; HLM) and low (mild reactivity; LLM) levels of myosin expression. Expression of p21 was higher in HLM-PRSs than in LLM-PRSs. Statistically significant association was observed between myosin and p21 expression in PRSs, but not between myosin and myogenin expression. Myogenin and p21 reactivity were observed in myoblast-like cells, but rarely in multinucleated cells. In ERSs, small undifferentiated myogenic precursor cells were also positive for p21. No difference of PCNA reactivity was observed between HLM-PRSs and LLM-PRSs, although its reactivity was higher in PRSs than in ERSs. The results suggest that myogenin is related to myoblast-like cell differentiation in PRSs and that p21 plays essential roles in myotube formation and myosin expression. In ERSs, p21 may be involved in inhibition of myogenic precursor cell proliferation and differentiation.

Figure 1

Histological features of methylcholanthrene (MC)-induced mouse rhabdomyosarcomas. (a) Embryonal rhabdomyosarcomas (ERS) is composed of small undifferentiated myogenic precursor cells and short spindle-shaped myoblast-like cells; 11 weeks postinjection (PI); haematoxylin and eosin (HE) staining (×153). (b) Pleomorphic rhabdomyosarcomas (PRS) is composed of large round, polygonal and elongated spindle cells with abundant eosinophilic cytoplasm, and multinucleated cells are common; 20 weeks PI; HE staining (×153). (c) Cross-striations are revealed in PRS; phosphotungstic acid haematoxylin staining (×153).

Figure 2

Immunohistochemistry for myogenin and p21 in methylcholanthrene (MC)-induced mouse rhabdomyosarcomas. (a) Embryonal rhabdomyosarcomas (ERS) shows marked myogenin nuclear reactivity; 11 weeks PI. (b) ERS shows moderate p21 nuclear reactivity; 10 weeks PI. (c) Pleomorphic rhabdomyosarcomas (PRS) shows moderate myogenin nuclear reactivity; 16 weeks PI. (d) PRS shows moderate p21 nuclear reactivity; 16 weeks PI. The amino acid polymer-peroxidase simple staining method/3-amino-9-ethylcarbazol. Counterstained with haematoxylin (×153).

Figure 3

Immunohistochemistry for myosin and proliferating cell nuclear antigen (PCNA) in methylcholanthrene (MC)-induced mouse rhabdomyosarcomas. (a) Embryonal rhabdomyosarcomas (ERS) shows moderate myosin cytoplasmic reactivity; 10 weeks PI. (b) ERS shows moderate PCNA nuclear reactivity; 11 weeks PI. (c) Pleomorphic rhabdomyosarcomas (PRS) shows moderate myosin cytoplasmic reactivity; 16 weeks PI. (d) PRS shows marked PCNA nuclear reactivity; 16 weeks PI. The amino acid polymer-peroxidase simple staining method/3-amino-9-ethylcarbazol. Counterstained with haematoxylin (×153).