RT @USCStemCell: Meet USC’s CIRM Scholar Alumna Joanna Smeeton, Assistant Professor at Columbia University. @smeetonlab @USCStemCell @KeckS….

RT @KECKSchool_USC: Partnering with @USCStemCell and @CIRMnews to train the next generation of leaders in stem cell research. Since 2006, C….

RT @JasonSynaptic: While I’m a big fan of new technologies that help us study human biology…there’s still no replacement for animal researc….

RT @USCStemCell: $13.5 million from a CIRM Scholars program at @USCStemCell has supported and will support 110 trainees, including PhD stud….

Great write up from Mathi on her PhD journey @USCStemCell @KECKSchool_USC.

RT @SocDevBio: The Society for Developmental Biology has released a statement on how the Abrupt Dismissal of NIH and NSF Staff Undermines G….

Nice article in Scientific American about our work on outer ear evolution and a complimentary study from the lab of Maksim Plikus on role of unique lipids in mammalian ear cartilage. @MathiThiru95 @USCStemCell @KECKSchool_USC .

You can view the PDF of our gills to outer ears paper here: Also the link to the article on Nature is now working again:

Our work challenges notions of evolutionary homology. While the function, position and cell type composition of gills and outer ears have greatly shifted, their use of a core gene regulatory program suggests deep homology beyond simply co-option. 14/n

Sutton also describes Egyptian goats with wattles containing elastic cartilage. Innervation by glossopharyngeal nerves suggests a third arch origin as with fish gills. Thus, the position of elastic cartilage outgrowths is dynamic even in mammals. 13/n

Our work may also explain rare human cervical chondrocutaneous branchial remnants. As described by Sutton in 1890, these outgrowths containing elastic cartilage appear on the neck, potentially reflecting atavism to a gill-like state. 12/n

Our cross-species enhancer testing suggests that an ancient gill gene regulatory program was used to make outer ears. In absence of fossil data, we cannot be sure if this involved successive modification of gills or repurposing of a gill program. 11/n

In single-cell multiomic profiling of book gills of the Atlantic horseshoe crab, we found a similar Dlx/distalless program for gill outgrowth. Remarkably, a horseshoe crab distalless enhancer drove transgenic gill expression in zebrafish.

In single-cell multiomic profiling of book gills of the Atlantic horseshoe crab, we found a similar Dlx/distalless program for gill outgrowth. Remarkably, a horseshoe crab distalless enhancer drove transgenic gill expression in zebrafish. 10/n

We next asked whether gill elastic-like cartilage might predate vertebrates. Work from Brian Hall, Philip Person, Martin Cohn, Daniel Medeiros, and others had suggested some invertebrates have cartilage-like tissue in their gills and tentacles. 9/n

While we were not able to test enhancer activity in reptiles, with Tom Lozito @USCStemCell we found that the extracolumella that supports the ear canal of the green anole lizard is an elastic cartilage morphologically similar to that in gills and outer ears. 8/n

But what happened during the evolution of fishes to mammals? With crucial help from Hellen Willsey @goodfrognosis, we tested fish gill and human outer ear enhancers in transgenic Xenopus tadpoles and found activity in nascent amphibian gills or their elastic cartilage. 7/n

Homology between fish gills and the outer ear extend beyond just elastic cartilage. We identified 27 gill outgrowth enhancers with sequence conservation in the human genome. One in the DLX5/6 locus drove expression in nascent fish gills. 6/n

Supporting enrichment of similar TF binding sites, 6/10 human outer ear enhancers were selectively active in the gills of transgenic fish. Reciprocally a zebrafish gill cartilage enhancer was selectively active in the outer ear of transgenic mice. 5/n

We also found that open chromatin regions indicative of enhancers for the human outer ear and zebrafish gills were enriched for many of the same transcription factor binding sites. 4/n