The Role of Scpp Genes in the Loss and Replacement of Scales in Catfishes

Flores, Kaylie

Undergraduate Honors Thesis

The Role of Scpp Genes in the Loss and Replacement of Scales in Catfishes Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/5712m806f

Abstract

Dollo’s Law of Irreversibility states that a species cannot regain a structure that it has previously lost. The function of a lost structure may be replaced by a similar one, however. An example of the latter phenomenon is found in catfishes (Siluriformes). Scales were lost in the common ancestor of this group and replaced in some lineages by bony plates known as scutes. Scutes are functionally similar to scales but are structurally distinct. I hypothesized that the genes involved in scale development were retained in “naked” catfish and redeployed in the origin of scutes. Members of the Secretory calcium-binding phosphoprotein (Scpp) gene family were examined because they are thought to have played an important role in the evolution of vertebrate hard tissues. The specific family members, scpp1 and scpp5, were chosen due to their known expression in bone and dental tissues of other species. Such tissues are found in both scales and scutes. By using an in situ hybridization approach to analyze the expression of scpp1 and scpp5 in the skin of three fish species, I have found both scpp1 and scpp5 to be expressed in the scales of zebrafish (Danio rerio – representing the ancestral condition), neither to be expressed in the trunk skin of the “naked” channel catfish (Ictalurus punctatus), and only scpp1 to be expressed in the scutes of an armored catfish (Corydoras fulleri). These results, along with the expression of the genes in other structures, such as teeth and fin rays, suggest that scale loss did not lead to loss of all the genes required for scale development. Retained genes, such as scpp1, are therefore available for redeployment in the development of replacement structures contributing to the evolvability of the integumentary (skin) skeleton.

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