KANGAS, AT*; MUSTONEN, T; MIKKOLA, ML; THESLEFF, I; JERNVALL, J; University of Helsinki, Finland; University of Helsinki, Finland; University of Helsinki, Finland; University of Helsinki, Finland; University of Helsinki, Finland: A Single-Gene Mutation Leads to Changes in Several Dental Characters in Mouse

Gene knockouts often lead to an early and total disruption of tooth development that makes them useless for the analysis of tooth crown formation. Because most of the dental characters which are commonly used in evolutionary studies develop during the crown formation, we investigated a gene mutation with a weaker tooth phenotype in order to compare developmental lability of different aspects of tooth shape. Ectodysplasin (Eda) is a cell signaling protein expressed during development of several ectodermal organs. Lack of functional Eda causes an ectodermal dysplasia syndrome in which the development of teeth, hair and ectodermal glands is disturbed but most teeth still develop. We analyzed the tooth phenotype of two mouse lineages. One was a natural mutant, Tabby which lacks functional Eda, and the other was a transgenic mouse line, K14-Eda which overexpresses Eda in its ectoderm. We examined how dental characters change when Eda activity levels rise from zero (Tabby) to normal (wild type controls), and much beyond normal (K14-Eda). We found that with increasing Eda levels, several aspects of tooth shape change: The number of cusps increases, cusp positions change, additional crests form, and number of teeth increases. These results indicate that different expression levels of one gene are capable of changing most of the character states of teeth used in taxonomy. While these changes in morphology represent extreme differences compared to typical population level variation, our results show how most tooth shape characters have the developmental potential for correlated changes during evolution.