Abstract
The extent to which ductal branch pattern is controlled by hard‐wired stereotypical mechanisms has been a long standing question in biology. In the mammary gland, prevailing wisdom has held that ductal patterning is stochastic. However, a detailed analysis of mammary ductal patterning using appropriate 3‐dimensional approaches has not been done. Prior published work from our group demonstrates that genetic background has a profound effect on mammary ductal patterning. The hypothesis for these experiments was that ductal patterning and the implementation of stereotypical branching behaviors during early postnatal development differs with genetic background. To test this hypothesis, 12 measures of ductal geometry and two of stereotypy were compared among 3D reconstructions derived from whole‐mounted mammary glands that were stained with the epithelial marker E‐cadherin and imaged by optical projection tomography. Samples were taken on postnatal day (PN) 17 from females of the C57BL/6J (N=5), PWK/PhJ (N=3), and KK/HlJ (N=3) strains. Comparison of graph size, defined as total number of branches, and total ductal length (mm) revealed that overall development was the greatest (P<0.05) in KK/HlJ (56.33±1.76, and 31.57±0.357, respectively), intermediate in C57BL/6J (50.33±6.16, and 23.67±.798, respectively), and least in the PWK/PhJ (41.60±3.12, and 20.51±1.39, respectively). The average local ductal bifurcation angles were also larger (P<0.05) in KK/HlJ than PWK/PhJ (107.01±0.67° and 95.45±3.39°, respectively). Lastly, as a measure of stereotypy, graph discordance was lowest (P<0.05) in KK/HlJ, intermediate in C67BL/6J, and highest in PWK/PhJ (0.47±0.013, 0.54±0.03, and 0.61±0.02, respectively). These results highlight the utility of 3D imaging methodologies in understanding mammary ductal development and support the conclusion that differences in ductal development among differing genetic backgrounds may also be linked with differential implementation of stereotypical patterning.Support or Funding InformationThis work supported by a grant from the DOD number DAMD‐0017.
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