Spatial and temporal expression pattern of POU-M1/SGF-3 in Bombyx mon embryogenesis

The expression pattern of the POU-M1/SGF-3 gene during Bombyx embryogenesis has been analysed using in situ hybridization and immunohistochemistry. At the early embryo retraction stage, both the transcripts and protein were first detected in precursor cells of the prothoracic glands in the labial segment, in the oenocytes in the A1-A8 segments and in invaginated regions in the mandibular and maxillary segments. The invaginated regions in the mandibular segment develop into the abductor plates in the lateral anterior region and the adductor plates in the posterior region. From the latter plates, the salivary glands elongate. The invaginated regions in the maxillary segment develop into the corpora allata in the anterior region and the subbuccal glands in the posterior region, which unite with tissues of the anterior region of the mandibular segment at later stages. After the embryo retraction stage, the transcripts and protein products also become detectable in the silk gland invagination points and, after the blastokinesis stage, the products are restricted to the entire anterior silk glands and to the anterior and middle parts of the middle silk glands. Expression can also be detected in a part of the hindgut, in the tracheal system and in some cells of the central nervous system. These results indicate that POU-M1/SGF-3 might play roles in the development of the silk glands, nervous system, tracheal system and other organs like the prothoracic glands and oenocytes.