Transformation of the Ancestral Body Plan and Axial Growth in Echinoderms: Ontogenetic and Paleontological Data

• Published in: Paleontological journal Vol. 56; no. 8; pp. 863 - 886
• Main Authors: Isaeva, V. V., Rozhnov, S. V.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.12.2022; Springer; Springer Nature B.V
• Subjects: Earth and Environmental Science; Earth Sciences; Echinodermata; Embryogenesis; Embryonic development; Embryonic growth stage; Evolution; Gene clusters; Genetic transformation; Growth; Homology; Invertebrates; Limb buds; Marine invertebrates; Metamorphosis; Molecular modelling; Ontogeny; Paleontology; Stem cells; Symmetry; Vectors; Vertebrates; Wnt protein; Nodal; axial body plan; Cambrian; Bilateria; BMP; Echinodermata; symmetry; pentamery; axial Hox-code; Ediacaran; preterminal growth zone; signaling systems Wnt
• ISSN: 0031-0301; 1555-6174
• DOI: 10.1134/S0031030122080032

Paleontological data on the appearance and development of metazoan axial symmetry are compared with molecular genetic evidence to determine the axial body plan and growth vectors of bilaterian organisms by the coordinated functioning cascades of signaling pathways Wnt , BMP , Nodal , Hedgehog, and regulatory Hox and ParaHox gene clusters. The axial body symmetry in most bilaterians is associated with the uniaxial growth vector. Posterior body growth ensured by the progenitor stem cell pool of the growth zone localized at the preterminal end of the body became a cardinal evolutionary innovation in Bilateria. The conservatism of ancestral molecular mechanisms of bilaterian body plan specification is combined with their flexibility, which provided the possibility of evolutionary transformations of the axial pattern of the organism. Radical evolutionary changes with the formation of additional growth zones are reported in the representatives of Deuterostomia (Vertebrata and Echinodermata). In modern vertebrates, while the main ancestral axis of body growth is preserved, two pairs of additional growth zones (limb buds) emerged. They are considered paramorphic homologs (replicates) of the posterior part of the main body axis. The pentamerous pattern of the body plan and growth of recent echinoderms can be explained as a result of the multiplication of the ancestral organizing center of axial architectonics and its radialization during larval metamorphosis (or in early embryogenesis during lecithotrophic development) with a corresponding multiplication of growth zones localized at the ends of rays (ambulacra). It is consistent with paleontological data and the concept of echinoderm rays as paramorphic homologs of the main body axis of the bilaterian ancestors of echinoderms.