Scale development in zebrafish (Danio rerio)

Abstract

In the course of an extensive comparative, structural and developmental study of the cranial and postcranial dermal skeleton (teeth and scales) in osteichthyan fishes, we have undertaken investigations on scale development in zebrafish (Danio (Brachydanio) rerio) using alizarin red staining, and light and transmission electron microscopy. The main goal was to know whether zebrafish scales can be used as a model for further research on the processes controlling the development of the dermal skeleton in general, especially epithelialmesenchymal interactions. Growth series of laboratory bred specimens were used to study in detail : (1) the relationship of scale appearance with size and age ; (2) the squamation pattern ; and (3) the events taking place in the epidermis and in the dermis, before and during scale initiation and formation, with the aim of searching for morphological indications of epithelial-mesenchymal interactions. Scales form late in ontogeny, generally when zebrafish are more than 8n0 mm in standard length. Within a population of zebrafish of the same age scale appearance is related to standard length, but when comparing populations of different age the size of the fish at scale appearance is also related to age. Scales always appear first in the posterior region of the body and the squamation then extends anteriorly. Scales develop in the dermis but closely apposed to the epidermal-dermal boundary. Cellular modifications occurring in the basal layer of the epidermis and in the dermis before scale formation clearly indicate that the basal epidermal cells differentiate first, before any evidence of differentiation of the progenitors of the scale-forming cells in the dermis. This strongly suggests that scale differentiation could be initiated by the epidermal basal layer cells which probably produce a molecular signal towards the dermis below. Subsequently dermal cells accumulate close to the epidermis, and differentiate to form scale papillae. The late formation of the scales during ontogeny is due to a late colonisation of the dermis by the progenitors of the scale-forming cells. Because of their late formation during ontogeny and of their regular pattern of development, scales in zebrafish represent a good model for further investigations on the general mechanisms of epithelial-mesenchymal interactions during dermal skeleton development, and in particular for the study of the gene expression patterns.

Scale development in fish: a review, with description of sonic hedgehog (shh) expression in the zebrafish (Danio rerio).

“…In a cichlid (Hemichromis bimaculatus) and in the zebrafish the developmental sequences strongly suggest that the cells of the basal epidermal layer are involved in the deposition of the limiting layer, i.e. that this tissue could contain epidermal (i.e., enamellike) products (Sire, 1988;Sire et al, 1997a) (Fig. 3).…”

“…Scale formation is, however, well studied at the tissue and cellular level (Sire and Géraudie, 1983;Sire et al, 1997aSire et al, , 1997b. These data are useful to infer homology of the fish scale by comparing its development with that of other elements of the dermal skeleton.…”

Epidermal transient down‐regulation of retinol‐binding protein 4 and mirror expression of apolipoprotein Eb and estrogen receptor 2a during zebrafish fin and scale development

“…4G,M) and sonic hedgehog (shh; Sire and Akimenko, 2004). Ultrastructural studies suggested that epidermal-dermal interactions continued to occur in the posterior region of the formed scale (Sire et al, 1997a). This process may be supported by the molecular patterning of apoeb and esr2a transcripts maintained in the posterior margin epidermis of the growing scales ( Fig.…”

“…In zebrafish, the first scales appear on the lateral and posterior part of the fish at the midregion of the caudal fin and squamation then spread forward, downward, and laterally (Waterman, 1970;Sire et al, 1997a;Sire and Akimenko, 2004). Starting from a homogeneous rbp4 expressed epidermal cover (Fig.…”

“…Thickening of the primary dermal stroma underlying the epidermis occurs during larval stages, and there is a remarkable remodeling and thickening of the larval skin during the larval-to-juvenile transition (Le Guellec et al, 2004). This metamorphosis entails changes in a variety of organ systems, including resorption of the larval fin fold and development of adult unpaired fins, development of scales in the integument, and formation of an adult pigment pattern (Brown, 1997;Sire et al, 1997a). Numerous studies have illustrated the morphogenesis of scales in teleost fish, including zebrafish (Waterman, 1970;Sire et al, 1997a,b;Sire and Akimenko, 2004).…”