Modes of Developmental Outgrowth and Shaping of a Craniofacial Bone in Zebrafish

Abstract

The morphologies of individual bones are crucial for their functions within the skeleton, and vary markedly during evolution. Recent studies have begun to reveal the detailed molecular genetic pathways that underlie skeletal morphogenesis. On the other hand, understanding of the process of morphogenesis itself has not kept pace with the molecular work. We examined, through an extended period of development in zebrafish, how a prominent craniofacial bone, the opercle (Op), attains its adult morphology. Using high-resolution confocal imaging of the vitally stained Op in live larvae, we show that the bone initially appears as a simple linear spicule, or spur, with a characteristic position and orientation, and lined by osteoblasts that we visualize by transgenic labeling. The Op then undergoes a stereotyped sequence of shape transitions, most notably during the larval period occurring through three weeks postfertilization. New shapes arise, and the bone grows in size, as a consequence of anisotropic addition of new mineralized bone matrix along specific regions of the pre-existing bone surfaces. We find that two modes of matrix addition, spurs and veils, are primarily associated with change in shape, whereas a third mode, incremental banding, largely accounts for growth in size. Furthermore, morphometric analyses show that shape development and growth follow different trajectories, suggesting separate control of bone shape and size. New osteoblast arrangements are associated with new patterns of matrix outgrowth, and we propose that fine developmental regulation of osteoblast position is a critical determinant of the spatiotemporal pattern of morphogenesis.

Genetic lineage labeling in zebrafish uncovers novel neural crest contributions to the head, including gill pillar cells

“…The evolution of the opercular series has facilitated a novel mechanism for the depression of the mandible (Lauder, 1980a;Lauder, 1980b;Lauder, 1982), allowing an improvement in suction feeding through better control over fluid movement (Lauder, 1980a). The NC origin of the opercular series, as conclusively shown using our long-term labeling approach, was previously assumed on the basis of its dermal bone composition and the expression of specific transgenes (Kimmel et al, 2010). Recent findings demonstrating the presence of an embryonic operculum in amniotes have rekindled interest in this 923 RESEARCH ARTICLE NC origin of gill pillar cells structure, which was presumed to have been lost completely with the evolution of tetrapods and the emergence of a terrestrial lifestyle (Richardson et al, 2012).…”

Postembryonic staging of wild‐type goldfish, with brief reference to skeletal systems

“…Comparative studies of ontogenetic process require not only embryonic, but also postembryonic staging tables, as several important morphogenetic processes which form characteristic features of each species (for example, internal and external skeletal structures and scale patterns) are known to proceed during postembryonic stages (Arratia et al, 1990, 1991; Cubbage and Mabee, 1996; Schilling and Kimmel, 1997; Van der Heyden and Huyssune, 2000; Van der Heyden et al, 2000; Witten et al, 2001; Yelick and Schilling, 2002; Mabee et al, 2002; Bird and Mabee, 2003; Sire and Huysseune, 2003; Webb and Shirey, 2003; Elizondo et al, 2005; Sire and Akimenko, 2004; Thorsen and Hale, 2005; Patricia et al, 2007; Patterson et al, 2008; Parichy et al, 2009; Kimmel et al, 2010; Budi et al, 2011; Bensimon‐Brito et al, 2012). However, at present there is no widely available postembryonic developmental staging table for goldfish, in practice.…”

Zebrafish sp7:EGFP: A transgenic for studying otic vesicle formation, skeletogenesis, and bone regeneration

“…Future studies could include dynamic analysis of changing bone shape during development (Kimmel et al, 2010), analysis of mutants that have altered dermal bone shape such as the mef2ca mutant (Miller et al, 2007), and analysis of genetic pathways and mechanisms of skeletal repair in response to injury.…”