# Development Genetics of Tooth Number Variation in Sticklebacks

> **NIH NIH R01** · UNIVERSITY OF CALIFORNIA BERKELEY · 2020 · $359,095

## Abstract

Project Summary
The expected overall impact of this project is to identify developmental and genetic mechanisms underlying
tooth formation and replacement. Teeth have classically been used as a model to study organogenesis, as
teeth, like most organs, develop through reciprocal epithelial-mesenchymal interactions. Furthermore, 30
percent of people worldwide over the age of 65 have no natural teeth. Thus, knowledge of the developmental
and genetic basis of tooth formation and replacement has relevance both for understanding organogenesis, as
well as for understanding how teeth can be regenerated in vitro and ultimately in vivo. Although genetic studies
in mice and humans have identified signaling pathways involved in tooth development, less is known about
genetic mechanisms regulating tooth replacement. Fish replace their teeth constantly throughout adult life, and
offer powerful systems for genetic analysis. Here, natural variation in tooth number in the threespine
stickleback fish (Gasterosteus aculeatus) is leveraged as a new model system to learn how genes regulate
tooth number and tooth replacement. Different stickleback populations adapted to different diets exhibit
dramatic heritable changes in tooth number. Two different, independently derived freshwater populations have
evolved major increases in tooth number compared to ancestral marine fish. In both high-toothed populations,
the tooth number increase arises late in development through an accelerated tooth replacement rate. The
different forms can be crossed in the lab, enabling detailed forward genetic analyses to map factors controlling
the changes in tooth number. New genome editing methods allow functional tests of genes and cis-regulatory
elements of interest. A cis-regulatory allele of the Bone Morphogenetic Protein 6 (Bmp6) gene is associated
with evolved tooth gain in one high-toothed population. Pharmacological and genetic data suggest BMP
signaling and Bmp6 positively regulate primary tooth number, but inhibit tooth replacement. To test hypotheses
about the developmental and genetic bases of tooth formation and replacement, three specific aims are
proposed. First, we will test whether BMP signaling and Bmp6 regulate dental stem cell quiescence during
tooth replacement by BrdU and vital dye pulse-chase labeling, gene expression, and pharmacological
experiments. Second, we will identify upstream regulators of two Bmp6 enhancers and determine enhancer
and regulator functions during tooth development and replacement by pharmacological, transgenic, and
genome editing experiments. Third, we will identify the genetic basis of evolved tooth gain in an independently
derived high-toothed freshwater population with a distinct developmental genetic basis by a combination of
genetic mapping, genome editing, and gene expression experiments. Together these results will shed new
light on developmental and genetic mechanisms underlying tooth replacement.

## Key facts

- **NIH application ID:** 9960489
- **Project number:** 5R01DE021475-10
- **Recipient organization:** UNIVERSITY OF CALIFORNIA BERKELEY
- **Principal Investigator:** Craig Thomas Miller
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $359,095
- **Award type:** 5
- **Project period:** 2011-03-01 → 2021-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9960489

## Citation

> US National Institutes of Health, RePORTER application 9960489, Development Genetics of Tooth Number Variation in Sticklebacks (5R01DE021475-10). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9960489. Licensed CC0.

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