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The Importance Of Understanding The Micro‐Environment Enabling Tissue Induction: A Case Study Of The Scleral Ossicle System
Author(s) -
FranzOdendaal Tamara,
Gaitor Danielle,
Drake Paige,
Giffin Jennifer
Publication year - 2021
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2021.35.s1.02080
Subject(s) - biology , ossicle , sclera , in situ hybridization , neural crest , microbiology and biotechnology , period (music) , gene , anatomy , gene expression , embryo , evolutionary biology , genetics , middle ear , physics , acoustics
Developmental induction is the cornerstone of many developmental processes, with research most often focused on identifying the inductive factors and/or tissues. Here, we examine the microenvironment that enables the inductive events that occur during development of the scleral ossicles. The scleral ossicle system of avians is composed of a series of 13‐16 flat neural‐crest derived overlapping bones situated in the sclera of the eye. The skeletogenic condensations, preceding these bones, develop over a two day period and are induced by placode‐derived conjunctival epithelial papillae. These placodes develop in a fascinating spatiotemporal pattern that is conserved across avians and reptiles. There is a gap in our understanding of the ontogenetic growth of these condensations and the factors that are involved in inducing the scleral ossicle system. Using a combination of histological analyses, qPCR and in situ hybridization gene expression analyses, we provide insight into the tissue characteristics of this system. We show that while the condensations increase in size, their relative depth remains constant, indicating that the distance inducing morphogens need to diffuse is constant over the two day period of induction despite scleral width increasing. Our gene expression analyses of the early inductive phases reveals a complex network of interacting factors, that are also implicated in epithelial placode induction in other systems. Specifically, several members of each of the following key signaling pathways ‐ β‐catenin, FGF, BMP, EDA and HH ‐ are expressed during placode formation. Correlation analyses reveal two distinct gene interaction modules providing evidence of subgroups of genes with unique spatiotemporal expression characteristics. Additionally, through careful embryonic manipulations, we created knock‐out phenotypes for both the placodes and the skeletogenic condensations. These phenotypes may be the result of vascular disruption and/or matrix disruption and demonstrates the importance of each in enabling inductive mechanisms. The mesenchymal matrix is denser in these knock‐outs, suggesting that diffusible morphogens cannot reach their destinations deeper in the tissue. Collectively these results underscore the importance of understanding the microenvironmental context that supports morphogen‐based tissue induction.