IMMUNOCYTOCHEMICAL ELECTRON-MICROSCOPIC STUDY AND WESTERN-BLOT-ANALYSIS OF CALDESMON AND CALPONIN IN STRIATED-MUSCLE OF THE FRUIT-FLY DROSOPHILA-MELANOGASTER AND IN SEVERAL MUSCLE-CELL TYPES OF THE EARTHWORM EISENIA-FOETIDA

Caldesmon and calponin are two proteins that are characteristic of ver tebrate smooth muscle. In invertebrates, caldesmon has only been studi ed in some molluscan muscles, and no previous references to calponin h ave been found. The aim of this paper was to investigate the presence and distribution of caldesmon and calponin in several invertebrate mus cle cell types, classified according to their ultrastructural pattern: transversely striated muscle (night muscle from Drosophila melanogast er), obliquely striated muscle (muscular body wall and inner muscular layer of the pseudoheart from the earthworm Eisenia foetida), and a mu scle of doubtful classification which seems to be intermediate between smooth muscle and obliquely striated muscle (outer muscular layer of the pseudoheart, from E. foetida), using electron microscopy immunocyt ochemistry and Western blot analysis. Immunoreactions to both caldesmo n and calponin were observed in the outer muscular layer cells from th e earthworm pseudoheart but neither in the transversely striated muscl e of D. melanogaster nor in the obliquely striated muscle from the ear thworm. Present findings suggest that caldesmon- and calponin-like pro teins are also present in invertebrate muscle cells, but only in those that are ultrastructurally similar to the vertebrate smooth muscle ce lls. Since discrepancies in the classification of some invertebrate mu scles are common in the literature, the use of distinctive markers, su ch as troponin, caldesmon and calponin may improve our understanding o f the nature and properties of many invertebrate muscles showing an ul trastructural pattern that does not resemble any of the classic muscle types.