Muscular Development in Urechis unicinctus (Echiura, Annelida)

• Published in: International journal of molecular sciences Vol. 21; no. 7; p. 2306
• Main Authors: Han, Yong-Hee, Ryu, Kyoung-Bin, Medina Jiménez, Brenda I, Kim, Jung, Lee, Hae-Youn, Cho, Sung-Jin
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 26.03.2020; MDPI
• Subjects: Actin; Actins - genetics; Actins - metabolism; Animals; Annelida; Annelida - growth & development; Annelids; Body wall; Calcium-binding protein; Calponin; Echiura; Embryogenesis; Embryos; Gene expression; Genes; Immunohistochemistry; Larvae; Major histocompatibility complex; Molecular modelling; Morphology; Muscle Development; Muscles; Muscles - metabolism; musculature; Nervous system; Nervous System - growth & development; Nervous System - metabolism; Sediments; Segmentation; Smooth muscle; Staining; striated muscle; Subgroups; Transcriptome; Troponin; Troponin I; Urechis unicinctus; Ventral nerve cord; smooth muscle; musculature; Echiura; Urechis unicinctus; striated muscle
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms21072306

Echiura is one of the most intriguing major subgroups of phylum Annelida because, unlike most other annelids, echiuran adults lack metameric body segmentation. lives in U-shape burrows of soft sediments. Little is known about the molecular mechanisms underlying the development of . Herein, we overviewed the developmental process from zygote to juvenile using immunohistochemistry and F-actin staining for the nervous and muscular systems, respectively. Through F-actin staining, we found that muscle fibers began to form in the trochophore phase and that muscles for feeding were produced first. Subsequently, in the segmentation larval stage, the transversal muscle was formed in the shape of a ring in an anterior-to-posterior direction with segment formation, as well as a ventromedian muscle for the formation of a ventral nerve cord. After that, many muscle fibers were produced along the entire body and formed the worm-shaped larva. Finally, we investigated the spatiotemporal expression of , , , and genes found in . During embryonic development, the striated and smooth muscle genes were co-expressed in the same region. However, the adult body wall muscles showed differential gene expression of each muscle layer. The results of this study will provide the basis for the understanding of muscle differentiation in Echiura.