No abstract

This is an author-produced, peer-reviewed version of this article. © 2009, Elsevier. Licensed under the Creative Commons AttributionNonCommercial-NoDerivatives 4.0 International License (https://creativecommons.org/licenses/by-nc-nd/4.0/). The final, definitive version of this document can be found online at Gene Expression Patterns, doi: 10.1016Patterns, doi: 10. /j.gep.2010 NOTICE: This is the author's version of a work accepted for publication by Elsevier. Changes resulting from the publishing process, including peer review, editing, corrections, structural formatting and other quality control mechanisms, may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. The definitive version has been published in Gene Expression Patterns, 2010. DOI: 10.1016/j.gep.2010 The Keywords: minor fibrillar collagens, zebrafish, development, in situ hybridization, Danio rerio Results and discussionCollagens are the predominant proteins in the extracellular matrix of animals. They play diverse roles in cell adhesion, differentiation, cell migration as well as tissue regeneration. Currently, there are at least 29 different collagens known (Söderhäll et al, 2007;Kadler et al, 2007). Generally, collagen fibrils are composed of three peptide alpha chains forming either heterotrimers or homotrimers. Depending on their functions and domain homology, collagens can be grouped into seven different types (Kadler et al, 2007). Collagen type I, II, III, V and XI as well as recently discovered XXIV and XXVII are fibril-forming collagens. Historically, the fibrillar collagens are further divided into major (I, II and III) and minor (V, XI, XXIV and XXVII) fibrillar collagens based on their relative abundance in the collagen fibrils. For collagen type V, three different alpha chains have been characterized in human: COL5A1, COL5A2 and COL5A3. Likewise, collagen type XI also has three alpha chains, COL11A1, COL11A2 and COL11A3. However, COL11A3 is actually COL2A1 (alpha1 chain, type II), one of the major fibrilforming collagens. Additionally, another alpha chain has been identified in rat, Col5a4, is expressed in Schwann cells and shows a high similarity to Col5a3 (Chernousov et al, 2000). However, Col5a4 has not been reported for other species.Minor fibril-forming collagens are composed of several domains, including the C-propeptide (NC1 or CPP), a major helix (COL1) and minor helix (COL2) separated by a short sequence (NC2), and the N-terminal end (NC3). The NC1 or CPP domain is well conserved among fibrilforming collagens, whereas NC3 domain varies in terms of size, primary structure and subdomains (Ricard-Blum, 2005). In the minor fibrillar collagens, NC3 contains either a cysteinerich repeat domain (CRR) feature with 10 cysteines in the sequence (Col5a2), or a thrombospondin Nterminal-like (TSPN) domain adjacent to a variable region (VR) (Col5a1, Col5a3, Col11a1 and Col11a2). The structural difference between Col5a2 and the other minor fibrillar collagens is in agreement with r...

Trigeminal sensory neurons develop from the neural crest and neurogenic placodes, and have been studied as a principle model of sensory neuron formation. While the Notch pathway has been extensively characterized in central nervous system development and other developmental processes, it has not been well characterized in sensory neurogenesis. Here we studied the functional role of Notch signaling in the trigeminal ophthalmic (opV) placode, a prime model of sensory neurogenesis. To establish a good spatiotemporal description of Notch pathway genes in the chick trigeminal placode, a stage-specific expression analysis was conducted, showing that expression of most Notch pathway genes and effectors are expressed in the placode, with expression primarily being confined to ectodermal cells. Expression was highest at stages of peak neuronal differentiation. To test the function of Notch signaling in opV placode cell differentiation, Notch receptor cleavage was blocked using the gamma-secretase inhibitor, DAPT, or signaling was activated by misexpression of the Notch intracellular domain (NICD). Notch activation resulted in a significant reduction in sensory neurogenesis. Cells remained in the ectoderm and did not differentiate. Expression of the opV specification marker Pax3 was also lost in targeted cells. DAPT exposure resulted in a dramatic increase in neurogenesis without increasing proliferation, where many differentiated cells were found in the mesenchyme and, surprisingly, within the ectoderm. This is the first result clearly showing prolific neuronal differentiation in the ectoderm of the trigeminal placodes after experimental manipulation of a molecular signaling pathway, thus identifying Notch signaling as a primary regulator of the sensory neuron fate in the opV placode.