We haven't explored this yet, but it is definitely an important question, and the Lamanna dataset would be the natural starting point.

If you want to learn more about the evolution of this fascinating cell type, make sure to also check out the beautiful study by @idoiaeu.bsky.social‬ on sharks www.biorxiv.org/content/10.1... end 🧵

Interestingly, Cajal-Retzius cells are VERY similar at the transcriptomic level to another ancestral cell type, the external tufted cell in the olfactory bulb. This suggests that Cajal-Retzius cells may have evolved in early vertebrates from cells involved in olfactory processing. 🧵 6/7

next, Eli and @giacomogattoni.bsky.social‬ hunted Cajal-Retzius cells in chicken 🐓 and three species of fish 🐟, to show that yes, this is an ancestral cell type in the vertebrate brain. 🧵 5/7

… Eli Gumnit started digging into our new salamander developmental scRNAseq dataset and, long story short, found that 80 cells (out of 127,788 cells) had an unmistakable Cajal-Retzius cell transcriptomic profile! 🧵 4/7

Given that a complex, six-layered cerebral cortex exists only in mammals, were Cajal-Retzius cells a mammalian innovation that transformed cortical development? The answer is: not really… 🧵 3/7

More than 100 years ago, Santiago Ramon y Cajal and Gustaf Retzius independently described intriguing neurons on the surface of the developing cortex. Decades later, Cajal-Retzius cells were found to release Reelin, a signaling molecule critical for the correct development of cortical layering 🧵 2/7

Congratulations Ish! We are so lucky to have you as a colleague here at Columbia!