TY  - JOUR
A1  - Hilgers, Leon
A1  - Hartmann, Stefanie
A1  - Hofreiter, Michael
A1  - von Rintelen, Thomas
T1  - Novel Genes, Ancient Genes, and Gene Co-Option Contributed o the Genetic Basis of the Radula, a Molluscan Innovation
JF  - Molecular biology and evolution
N2  - The radula is the central foraging organ and apomorphy of the Mollusca. However, in contrast to other innovations, including the mollusk shell, genetic underpinnings of radula formation remain virtually unknown. Here, we present the first radula formative tissue transcriptome using the viviparous freshwater snail Tylomelania sarasinorum and compare it to foot tissue and the shell-building mantle of the same species. We combine differential expression, functional enrichment, and phylostratigraphic analyses to identify both specific and shared genetic underpinnings of the three tissues as well as their dominant functions and evolutionary origins. Gene expression of radula formative tissue is very distinct, but nevertheless more similar to mantle than to foot. Generally, the genetic bases of both radula and shell formation were shaped by novel orchestration of preexisting genes and continuous evolution of novel genes. A significantly increased proportion of radula-specific genes originated since the origin of stem-mollusks, indicating that novel genes were especially important for radula evolution. Genes with radula-specific expression in our study are frequently also expressed during the formation of other lophotrochozoan hard structures, like chaetae (hes1, arx), spicules (gbx), and shells of mollusks (gbx, heph) and brachiopods (heph), suggesting gene co-option for hard structure formation. Finally, a Lophotrochozoa-specific chitin synthase with a myosin motor domain (CS-MD), which is expressed during mollusk and brachiopod shell formation, had radula-specific expression in our study. CS-MD potentially facilitated the construction of complex chitinous structures and points at the potential of molecular novelties to promote the evolution of different morphological innovations.
KW  - chitin synthase
KW  - novelty
KW  - radula
KW  - RNAseq
KW  - shell
KW  - Tylomelania sarasinorum
Y1  - 2018
U6  - https://doi.org/10.1093/molbev/msy052
SN  - 0737-4038
SN  - 1537-1719
VL  - 35
IS  - 7
SP  - 1638
EP  - 1652
PB  - Oxford Univ. Press
CY  - Oxford
ER  -