Actinotrichia collagens and their role in fin formation

Abstract

The skeleton of zebrafish fins consists of lepidotrichia and actinotrichia. Actinotrichia are fibrils located at the tip of each lepidotrichia and play a morphogenetic role in fin formation. Actinotrichia are formed by collagens associated with non-collagen components. The non-collagen components of actinotrichia (actinodins) have been shown to play a critical role in fin to limb transition. The present study has focused on the collagens that form actinotrichia and their role in fin formation. We have found actinotrichia are formed by Collagen I plus a novel form of Collagen II, encoded by the col2a1b gene. This second copy of the collagen II gene is only found in fishes and is the only Collagen type II expressed in fins. Both col1a1a and col2a1b were found in actinotrichia forming cells. Significantly, they also expressed the lysyl hydroxylase 1 (lh1) gene, which encodes an enzyme involved in the post-translational processing of collagens. Morpholino knockdown in zebrafish embryos demonstrated that the two collagens and lh1 are essential for actinotrichia and fin fold morphogenesis. The col1a1 dominant mutant chihuahua showed aberrant phenotypes in both actinotrichia and lepidotrichia during fin development and regeneration. These pieces of evidences support that actinotrichia are composed of Collagens I and II, which are post-translationally processed by Lh1, and that the correct expression and assembling of these collagens is essential for fin formation. The unique collagen composition of actinotrichia may play a role in fin skeleton morphogenesis.

Bone morphogenetic protein signaling promotes morphogenesis of blood vessels, wound epidermis, and actinotrichia during fin regeneration in zebrafish

“…Actinotrichia are skeletal spikes composed of actinodin and collagen proteins that support the distal margin of the fin (18,37). The mechanisms regulating actinotrichia regeneration in adult fin are unknown.…”

“…The mechanisms regulating actinotrichia regeneration in adult fin are unknown. We developed antibodies against And1, which is an essential component of these skeletal structures (18,37). At 3 dpa, we detected actinotrichial fibers between the wound epidermis and the blastema (Fig.…”

An exclusively mesodermal origin of fin mesenchyme demonstrates that zebrafish trunk neural crest does not generate ectomesenchyme

“…We suspect their function at this location is in modelling/repair of the ECM at these sites, in particular the actinotrichia of the distal adult lepidotrichia, mirroring their larval role. Indeed, during regeneration these cells have been observed to accumulate at the distal tip of the blastema (Nechiporuk and Keating, 2002;Poleo et al, 2001;Tu and Johnson, 2011), where actinotrichia form to guide regrowing lepidotrichia (Asharani et al, 2012;Durán et al, 2011). The regenerative plasticity of these fibroblasts within this distal blastema has been of interest to the fin regeneration field for a number of years; however, a number of recent reports indicate that fibroblasts do not normally regenerate other lineages after fin amputation (Knopf et al, 2011;Sousa et al, 2011;Stewart and Stankunas, 2012;Tu and Johnson, 2011).…”

Osteogenic programs during zebrafish fin regeneration

“…19,[28][29][30] Moreover, the sequential activation of runx2a/runx2b followed by sp7 during fin regeneration parallels the temporal activation of these genes during mammalian osteoblastic differentiation, Calcein (7dpa) / Alizarin Red (14dpa) sp7 :EGFP (10dpa) Zebrafish bone regeneration CJ Watson and RY Kwon suggesting conserved roles for these genes in modulating the progression of the differentiation program. 31 Orthologs for established markers of later osteoblast differentiation and mineralization such as osteopontin, 32 osteocalcin, 30 collagen 1a1 6 and alkaline phosphatase 33 have been detected in the fins of zebrafish (or related species) as well. The expression of these factors has been less well-characterized relative to earlier markers and further studies are needed to determine if fin regeneration can lend insight into the molecular events underlying late-stage osteogenic processes such as osteoblast maturation, mineral accrual and post-outgrowth apposition.…”

“…For example, at the cellular level, zebrafish bone is composed of many of the same components as mammalian bone, including osteoclasts, osteoblasts and osteocytes. 5 Physicochemical commonalities include the presence of type I collagen 6 and hydroxyapatite. 7 At the subcellular level, a growing number of genes mediating bone development, homeostasis and regeneration in mammals appear to be highly conserved in zebrafish, both in regard to their amino acid sequence and spatiotemporal expression profiles.…”