TCTN1 is the founding member of the Tectonic protein family, a group of evolutionarily conserved secreted and transmembrane proteins that regulate the Hedgehog (Hh)-mediated patterning of the neural tube. During embryonic development, TCTN1 is expressed in regions that participate in Hh signaling, beginning in the gastrulation stages in the ventral node. Mice expressing mutant TCTN1 die between E13.5 and E16.5 and display holoprosencephaly, a defect associated with reduced Hh signaling, indicating the role of TCTN1 as an Hh activator. At later stages in development, TCTN1 is thought to also act as a repressor on the Hh pathway in the anterior and posterior neural tube.