The emergence of сhordin-like1 in Gnathostomes may have contributed to the evolution of paired appendages

Andrey V Bayramov^1,2,3,4*Galina Ermakova^1,3Irina V Meyntser⁵Nikolai Muugue^2,4,6,7Vassily A. Lyubetsky^8,9Andrey G Zaraisky^{1,10,11,2,3,4}

• ¹Institute of Bioorganic Chemistry (RAS), Moscow, Russia
• ²FGBUN Institut biologii razvitia imeni N K Kol'cova Rossijskoj akademii nauk, Moscow, Russia
• ³FBGUN Institut bioorganiceskoj himii im akademikov M M Semakina i U A Ovcinnikova Rossijskoj akademii nauk, Moscow, Russia
• ⁴Koltzov Institute of Developmental Biology of Russian Academy of Sciences, Moscow, Russia
• ⁵Moskvarium, Moscow, Russia
• ⁶Russian Federal Research Institute Of Fisheries and Oceanography (VNIRO), Moscow, Russia
• ⁷FGBNU Vserossijskij naucno-issledovatel'skij institut rybnogo hozajstva i okeanografii, Moscow, Russia
• ⁸Institute for Information Transmission Problems of the Russian Academy of Sciences (Kharkevich Institute), Moscow, Russia
• ⁹Institut problem peredaci informacii imeni A A Harkevica RAN, Moscow, Russia
• ¹⁰Rossijskij nacional'nyj issledovatel'skij medicinskij universitet imeni N I Pirogova, Moscow, Russia
• ¹¹Pirogov Russian National Research Medical University, Moscow, Russia

Genomic transformations during early vertebrate evolution, including two rounds of wholegenome duplications, served as a prerequisite for the emergence of novel morphological structures in jawed vertebrates. Among these innovations are paired appendages, the development and diversification of which enabled vertebrates to exploit a wide range of ecological niches in aquatic, terrestrial, and aerial environments. In the present study, analysis of chordin-like gene homologs in vertebrates revealed that the gene chordin-like1 first appears in jawed vertebrates, and its emergence correlates with the origin of paired appendages. To investigate the potential link between the appearance of chordin-like1 and the evolution of paired appendages, we analyzed its expression in representatives of basal jawed vertebrate lineages: cartilaginous fishes (exemplified by the grey catshark Chiloscyllium griseum) and sturgeons (exemplified by the sterlet Acipenser ruthenus). In addition, we examined the expression patterns and functional properties of the chordin-like1 ortholog in the African clawed frog (Xenopus laevis), a representative of terrestrial vertebrates whose limb morphology differs markedly from the fins of basal gnathostomes. Our findings, together with literature data, suggest a possible involvement of chordin-like1 in the evolution of paired appendages, potentially playing a key role in the development of the metapterygial element and its derivatives, which became the structural basis for the evolution of tetrapod limbs.Among extant vertebrates, paired appendages are a unique feature of gnathostomes (jawed vertebrates) (Coates, 2003;Freitas et al., 2014). Although paired appendages have been identified in fossil jawless vertebrates, current data on their endoskeletal structure remain incomplete, making it difficult to establish homology with the appendages of living vertebrates (Coates, 2003;Enny et al., 2020;Bayramov et al., 2024). The origin of paired appendages has been a subject of continuous scientific interest since the 19th century. Several hypotheses have been proposed, among which the most influential are the lateral fin-fold theory -proposed by