Three‐dimensional fine structure of fibroblasts and other mesodermally derived tissues in the dermis of adults of the Bahamas lancelet (Chordata, Cephalohordata), as seen by serial block‐face scanning electron microscopy. (15th August 2022)

• Record Type: Journal Article
• Authors: Holland, Nicholas D.; Holland, Linda Z.; Somorjai, Ildiko M. L.
• Is Part Of: Journal of morphology. Volume 283:Number 10(2022)
• Page Start: 1289
• Page End: 1298
• Publication Date: 2022-08-15
• Subjects: amphioxus -- extracellular matrix -- midline mesoderm -- posteriormost segment -- telocyte; Morphology -- Periodicals; Physiology -- Periodicals; Anatomy -- Periodicals; 571.3
• DOI: 10.1002/jmor.21502
• Languages: English
• ISSNs: 0362-2525

Abstract

Abstract: Tissues of adult cephalochordates include sparsely distributed fibroblasts. Previous work on these cells has left unsettled such questions as their developmental origin, range of functions, and even their overall shape. Here, we describe fibroblasts of a cephalochordate, the Bahamas lancelet, Asymmetron lucayanum, by serial block‐face scanning electron microscopy to demonstrate their three‐dimensional (3D) distribution and fine structure in a 0.56‐mm length of the tail. The technique reveals in detail their position, abundance, and morphology. In the region studied, we found only 20 fibroblasts, well separated from one another. Each was strikingly stellate with long cytoplasmic processes rather similar to those of a vertebrate telocyte, a possibly fortuitous resemblance that is considered in the discussion section. In the cephalochordate dermis, the fibroblasts were never linked with one another, although they occasionally formed close associations of unknown significance with other cell types. The fibroblasts, in spite of their name, showed no signs of directly synthesizing fibrillar collagen. Instead, they appeared to be involved in the production of nonfibrous components of the extracellular matrix—both by the release of coarsely granular dense material and by secretion of more finely granular material by the local breakdown of their cytoplasmic processes. For context, the 3D structures of two other mesoderm‐derived tissues (the midline mesoderm and the posteriormost somite) are also described for the region studied. Abstract : For an adult cephalochordate, we use serial block‐face scanning electron microscopy (SBSEM) to reconstruct three‐dimensional fine structure of cells comprising the tail dermis (here in right‐side view at the top and left‐side view at the bottom). Special attention is given to the stellate fibroblasts (shown in red in the context of the blue central nervous system and green notochord tissue). The SBSEM corrects long‐standing misunderstandings about the shape of cephalochordate fibroblasts and clarifies their association with the neighboring tissue, indicating they synthesize granular (not, at least initially, fibrillar) components of the extracellular matrix of the dermis.