Mammalian hemicentin 1 is assembled into tracks in the extracellular matrix of multiple tissues

Abstract

Background: Hemicentins (HMCNs) are a family of extracellular matrix proteins first identified in Caenorhabditis elegans, with two orthologs (HMCN1 and 2) in vertebrates. In worms, HMCN is deposited at specific sites where it forms long, fine tracks that link two tissues by connecting adjacent basement membranes (BMs). By generating CRISPR/Cas9-mediated Hmcn1 and Hmcn2 knockout mice, we tested the hypothesis that HMCNs perform similar functions in mammals.Results: Hmcn1 −/− mice were viable and fertile. Using new, knockout mousevalidated HMCN1 antibodies, HMCN1 was detected in wild-type mice as fine tracks along the BM of hair and whisker follicles, in the sclera of the eyes, and in the lumen of some lymphoid conduits. It was also observed in the mesangial matrix of the kidney glomerulus. However, HMCN1 deficiency did not affect the functions of these tissues, including adherence of coat hairs and whiskers, the sieving function of lymphoid conduits, or the immune response to injected antigens. HMCN2 deficiency did not lead to any discernible phenotypes on its own or when combined with HMCN1 deficiency.Conclusion: That Hmcn1 −/− , Hmcn2 −/− , and Hmcn1/2 double knockout mice did not display any overt phenotypes implicates compensation by other members of the fibulin family. K E Y W O R D Sbasement membrane, hair follicle, lymphoid conduits, matrix protein, sclera, whisker follicle

Hemicentin-1 is An Essential Extracellular Matrix Component of the Dermal-Epidermal and Myotendinous Junctions

“…Hmcn1 is mainly produced by mesenchymal cells, while Hmcn2 appears to be expressed by cells of epithelial origin. Consistent with previous reports [15], Hmcn1 -/mice generated in this study via conventional gene recombination technology, although lacking detectable Hmcn1 protein, are viable and show no obvious morphological, mechanical or locomotion phenotypes. However, transmission electron microscopy revealed ultrastructural BM alterations at the DEJ and MTJ of Hmcn1 -/mice, pointing to a thus far unknown essential role of mouse Hmcn1 for BM integrity as the prerequisite for proper tissue linkage.…”

“…In mice, there are conflicting results about the importance of Hmcn1 for embryonic development. While it was initially reported that genetic ablation of Hmcn1 in mice leads to preimplantation lethality [17], a recent report showed that Hmcn1 is dispensable for murine embryogenesis [15]. To assess the functional roles of Hmcn1 and Hmcn2 during murine development, we analyzed their gene expression and their protein localization patterns at the two-cell stage (Fig.…”

“…Until now, comparably little data has been gained about the tissue localization and function of Hemicentins in mammals. Recently, it was shown that Hmcn1 forms fine extracellular tracks along the BM of some elastic tissue structures in hair, the lumen of lymphoid conduits, and the mesangial matrix of the kidney glomerulus [15]. However, the functions of these tracks remain obscure, especially since genetic ablation of Hmcn1, Hmcn2, as well as the double knock-out generated via CRISPR/Cas9 technology did not result in overt phenotypic changes in these tissues [15].…”

“…Recently, it was shown that Hmcn1 forms fine extracellular tracks along the BM of some elastic tissue structures in hair, the lumen of lymphoid conduits, and the mesangial matrix of the kidney glomerulus [15]. However, the functions of these tracks remain obscure, especially since genetic ablation of Hmcn1, Hmcn2, as well as the double knock-out generated via CRISPR/Cas9 technology did not result in overt phenotypic changes in these tissues [15]. Furthermore, due to the lack of specific Hmcn2 antibodies the tissue localization of Hmcn2 in mice has not been determined [15].…”

“…However, the functions of these tracks remain obscure, especially since genetic ablation of Hmcn1, Hmcn2, as well as the double knock-out generated via CRISPR/Cas9 technology did not result in overt phenotypic changes in these tissues [15]. Furthermore, due to the lack of specific Hmcn2 antibodies the tissue localization of Hmcn2 in mice has not been determined [15]. It is therefore not clear whether Hemicentins may functionally compensate for each other due to their mutual presence in specialized tissue microenvironments.…”