Network Monitoring of Adhesion/Growth-Regulatory Galectins: Localization of the Five Canonical Chicken Proteins in Embryonic and Maturing Bone and Cartilage and Their Introduction as Histochemical Tools

Divergence from an ancestral gene leads to a family of homologous proteins. Whether they are physiologically distinct, similar, or even redundant is an open question in each case. Defining profiles of tissue localization is a step toward giving diversity a functional meaning. Due to the significance of endogenous sugar receptors (lectins) as effectors for a wide range of cellular activities we have focused on galectins. The comparatively low level of network complexity constituted by only five canonical proteins makes chicken galectins (CGs) an attractive choice to perform comprehensive analysis, here studied on bone/cartilage as organ system. Galectin expression was monitored by Western blotting and immunohistochemistry using non-cross-reactive antibodies. Overall, three galectins (CG-1B, CG-3, CG-8) were present with individual expression patterns, one was found exclusively in the mesenchyme (CG-1A), the fifth (CG-2) not being detectable. The documented extents of separation are a sign for functional divergence; in cases with overlapping stainings, as for example in the osteoprogenitor layer or periosteum, cooperation may also be possible. Recombinant production enabled the introduction of the endogenous lectins as tools for binding-site localization. Their testing revealed developmental regulation and cell-type-specific staining. Of relevance for research on mammalian galectins, this study illustrates that certain cell types can express more than one galectin, letting functional interrelationships appear likely. Thus, complete network analysis irrespective of its degree of complexity is mandatory.