IMAGE: Joan Richtsmeier, distinguished professor of anthropology, Penn State. view more
Credit: Penn State
Joan Richtsmeier, distinguished professor of anthropology, is the recipient of the American Association of Anatomists’ 2019 Henry Gray Scientific Achievement Award. The award is the AAA’s most prestigious scientific award, presented annually to a member in recognition of unique and meritorious contributions to, and achievements in, the anatomical sciences.
Richtsmeier’s work focuses on determining the contribution of developmental processes to morphological variation. She has investigated differences in craniofacial growth patterns between primate species, between the sexes, and between children with craniofacial anomalies and typically developing children. To understand prenatal development of the head, she studies mice that carry mutations that when present in humans are associated with craniofacial disease like craniosynostosis in which sutures between the bones of the skull are closed prematurely. In this way, she and her team characterize the relationship between the genetic variants associated with premature cranial suture fusion and the craniofacial phenotypes — observable characteristics — associated with these mutations. Richtsmeier also studies a mouse model for Down syndrome to understand the influence of aneuploidy — an unusual number of chromosomes — on the production of phenotypes.
Currently, Richtsmeier is investigating the chondrocranium — the first skull to form during embryonic development, composed of cartilage — which in humans and most other vertebrates is replaced by bone during development. Through a $3.7 million grant from the National Institutes of Health’s National Institute of Dental and Craniofacial Research, she is studying the development of the chondrocranium in embryos of mice carrying some of these same disease-associated mutations.
“If we can see what is happening prenatally, it can help us understand what drives the development of disease phenotypes and to more fully understand what happens after birth,” said Richtsmeier.
Prenatally, the brain is grows very fast and cartilage provides a flexible but strong encasement that can grow internally through cell division and on the surface by accretion, enabling swift changes in shape.
“Our feeling was that an early skull made entirely of cartilage could accommodate swift changes in shape that occur during early development. As growth slows, bone that can grow by accretion only, replaces much of the cartilage, providing a stronger, though less-malleable protective exterior,” said Richtsmeier.
In the past, the morphology of the chondrocranium was not necessarily well-known to craniofacial biologists, but now is very familiar to evolutionary biologists. Kazuhiko Kawasaki, assistant research professor of anthropology, is an evolutionary geneticist who led the original work on the chondrocranium on which the researchers’ NIH grant is based.
According to Richtsmeier, “the presence and likely necessity of a cartilaginous skull that precedes the development of the bony skull was not widely recognized. Our goal is to understand how the bony skull forms to replace the primary cartilaginous skull that protects the early brain and sense organs. That process is unknown.”
Richtsmeier’s team uses microcomputed tomography to create 3D reconstructions of the mouse brain and its surrounding tissues. These images are used to visualize and measure the chondrocranium, forming skull, and other cranial soft tissues. The goal is to provide the first temporally precise, 3D reconstructions of the developing chondrocranium of the laboratory mouse and crucial information about its role in normal craniofacial development and in craniofacial anomalous conditions.
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