Biology
Developmental architecture of the nervous system in Themiste lageniformis (Sipuncula): New evidence from confocal laser scanning microscopy and gene expression
Document Type
Article
Abstract
Sipuncula is a clade of unsegmented marine worms that are currently placed among the basal radiation of conspicuously segmented Annelida. Their new location provides a unique opportunity to reinvestigate the evolution and development of segmented body plans. Neural segmentation is clearly evident during ganglionic ventral nerve cord (VNC) formation across Sedentaria and Errantia, which includes the majority of annelids. However, recent studies show that some annelid taxa outside of Sedentaria and Errantia have a medullary cord, without ganglia, as adults. Importantly, neural development in these taxa is understudied and interpretation can vary widely. For example, reports in sipunculans range from no evidence of segmentation to vestigial segmentation as inferred from a few pairs of serially repeated neuronal cell bodies along the VNC. We investigated patterns of pan-neuronal, neuronal subtype, and axonal markers using immunohistochemistry and whole mount in situ hybridization (WMISH) during neural development in an indirect-developing sipunculan, Themiste lageniformis. Confocal imaging revealed two clusters of 5HT+ neurons, two pairs of FMRF+ neurons, and Tubulin+ peripheral neurites that appear to be serially positioned along the VNC, similar to other sipunculans, to other annelids, and to spiralian taxa outside of Annelida. WMISH of a synaptotagmin1 ortholog in T. lageniformis (Tl-syt1) showed expression throughout the centralized nervous system (CNS), including the VNC where it appears to correlate with mature 5HT+ and FMRF+ neurons. An ortholog of elav1 (Tl-elav1) showed expression in differentiated neurons of the CNS with continuous expression in the VNC, supporting evidence of a medullary cord, and refuting evidence of ontogenetic segmentation during formation of the nervous system. Thus, we conclude that sipunculans do not exhibit any signs of morphological segmentation during development.
Publication Title
Journal of Morphology
Publication Date
11-2019
Volume
280
Issue
11
First Page
1628
Last Page
1650
ISSN
0362-2525
DOI
10.1002/jmor.21054
Keywords
Annelida, elav, nervous system, Sipuncula, synaptotagmin
Repository Citation
Carrillo-Baltodano, Allan M.; Boyle, Michael J.; Rice, Mary E.; and Meyer, Néva P., "Developmental architecture of the nervous system in Themiste lageniformis (Sipuncula): New evidence from confocal laser scanning microscopy and gene expression" (2019). Biology. 387.
https://commons.clarku.edu/faculty_biology/387
Cross Post Location
Student Publications