CYYR1: a new gene involved in Hh-mediated myogenesis and neuromasts differentiation during zebrafish development.

CYYR1 (Cysteine/tyrosine-rich 1) is a gene cloned in 2002 on human chromosome 21 that encodes a putative cysteine and tyrosine-rich protein and defines a new family of highly conserved vertebrate-specific genes. A detailed analysis of the human CYYR1 locus revealed the presence of a multitranscript-system that includes alternative spliced isoforms and one ncRNA gene overlapping CYYR1 in antisense orientation. Some observations and original results suggest the need of further investigations in order to verify a putative role of CYYR1 in the tumorigenic process, caused by dysfunction of cell differentiation and possibly related to the Hh pathway; to date, the specific function of the CYYR1 product is still unknown. The zebrafish cyyr1 is present in single copy and maintains almost 58% of identity with human protein therefore, we decided to perform a full characterization of cyyr1 expression and function using zebrafish as model system. WISH approach defined a broad expression in central nervous system (CNS), somites and muscles during somitogenesis and at 24-48 hpf. The cyyr1 knock-down with two different MOs targetting the ATG and the first splice-site of the transcript, affected both CNS and muscle development with a significant rescue in embryo co-injected with cyyr1 mRNA. Defects were also evident in cyliated cells of neuromast of the lateral line. Morphologically, the cyyr1-MOs injected embryos display some features of embryos inhibited for the Hh pathway through injection of the lefty mRNA and cyyr1 expression was significantly inhibited following Hh inhibition. Interestingly, the injection of cyyr1 mRNA was able to partially rescue Hh-defective phenotype in embryos at 24 hpf. These data have encouraged us to better investigate Hh-mediated developmental process such as myogenesis and the possible interplay between cyyr1 and Hh-pathway. Results obtained through different approaches such as immunofluorescent staining, qPCR and western blotting, support a role for cyyr1 in primary myogenesis probably downstream of Hh pathway.