Why Nipples Grow at the Front?

During the womb development, nipple will grow on front and the spine in the back. A team at the University of Auckland has also found why, in a research published in Nature Cell Biology.

The gene Runx2 was already known to control bone development, but the researchers led by Dr Maria Flores, senior research fellow of the university's school of medical sciences, have discovered it is the regulator dictating the development of a front and a back of the body.

The team was investigating genes controlling the development of the gut immune system of zebrafish, similar to the human genetic pathways, in order to detect genes involved in human diseases, like Crohn's, when this role of Runx2 was observed.
During the embryo development, genes are activated for creating various axes, for defining the parts of the body: left and right, top and bottom, and front and back. The Runx2 gene was found to dictate the development of a different front and back, monitoring their correct growth.

"When an egg is fertilized and the embryo starts to develop, these axes are genetically determined in the fertilized egg. What happens is that each of these axes tell the embryo what's going to be head and tail, left or right, or front or back. It turns out that Runx2 is an absolutely central gene in telling the embryo what's front and what's back," said molecular medicine specialist Associate Professor Phil Crosier, supervisor of Flores.

"Here supposedly a symmetrically shaped egg gets fertilized, gets turned into this multicellular incredibly complex organism, and so you have to set up these ground rules - in essence, the rules of the game in genetic terms," said Crosier.
This gene is crucial in stem cell development, but also in cancer development.

"The three runx genes have all been linked with cancers; the Runx1 in acute myeloid leukemia, Runx2 in cancer's metastasis or spread and Runx3 in gastric cancer," said Flores.

"Understanding the genes' role in embryonic development could mean better knowledge of how cancer develops. Many of these genes that are important in early embryonic development also turn out to be targets of disease processes like cancer, and that's a recurring theme now in biomedical research," said Crosier.