Tail regeneration in a cephalochordate, the Bahamas lancelet, Asymmetron lucayanum. (12th November 2020)

• Record Type: Journal Article
• Authors: Holland, Nicholas D.; Somorjai, Ildiko M. L.
• Is Part Of: Journal of morphology. Volume 282:Number 2(2021)
• Page Start: 217
• Page End: 229
• Publication Date: 2020-11-12
• Subjects: amphioxus -- Cephalochordata -- serial blockface scanning electron microscopy (SBSEM); Morphology -- Periodicals; Physiology -- Periodicals; Anatomy -- Periodicals; 571.3
• DOI: 10.1002/jmor.21297
• Languages: English
• ISSNs: 0362-2525

Abstract

Abstract: Lancelets (Phylum Chordata, subphylum Cephalochordata) readily regenerate a lost tail. Here, we use light microscopy and serial blockface scanning electron microscopy (SBSEM) to describe tail replacement in the Bahamas lancelet, Asymmetron lucayanum . One day after amputation, the monolayered epidermis has migrated over the wound surface. At 4 days, the regenerate is about 3% as long as the tail length removed. The re‐growing nerve cord is a tubular outgrowth of ependymal cells, and the new part of the notochord consists of several degenerating lamellar cells anterior to numerous small vacuolated cells. The cut edges of the mesothelium project into the regenerate as tubular extensions. These tubes anastomose with each other and with midline mesodermal canals beneath the regenerating edges of the dorsal and ventral fins. SBSEM did not reveal a blastema‐like aggregation of undifferentiated cells anywhere in the regenerate. At 6 days, the regenerate (10% of the amputated tail length) includes a notochord in which the small vacuolated cells mentioned above are differentiating into lamellar cells. At 10 days, the regenerate is 22% of the amputated tail length: myocytes have appeared in the walls of the myomeres, and sclerocoels have formed. By 14 days, the regenerate is 35% the length of the amputated tail, and the new tissues resemble smaller versions of those originally lost. The present results for A. lucayanum, a species regenerating quickly and with little inter‐specimen variability, provide the morphological background for future cell‐tracer, molecular genetic, and genomic studies of cephalochordate regeneration. Abstract : An amputated tail readily regenerates in cephalochordates (commonly called amphioxus or lancelets). In our study of tail regeneration in the Bahamas lancelet, we included serial blockface scanning electron microscopy (SBSEM) to make three‐dimensional reconstructions of the regenerating structures. In the regenerating tail of the 4‐day amputee, the central nervous system (CNS) is dorsal to the notochord, which consists of mature lamellar cells (LC, cytoplasm is various colors) and newly‐produced small vacuolated cells (SVC, green nuclei shown). Importantly, the comprehensive SBSEM reconstructions did not reveal a blastema‐like aggregation of undifferentiated cells anywhere in the regenerate.