Primary cilia are thin projections that are present on most cell types and that serve critical functions during multiple biological processes, including embryonic development. They are present in a single copy per cell and act much like an antenna, receiving and sending signals to the environment. This makes them crucial for coordinating cellular processes early in life.

Mutations in genes related to primary cilia (and/or motile cilia) cause a range of diseases collectively called ciliopathies, which are associated with multiple symptoms, many of which relate to developmental abnormalities. There are hundreds of genes known to be related to the formation, structure and function of primary cilia, but rather little is still known about the transcriptional regulators that coordinate the expression of all these "cilia genes". In a recent study, Liang et al. went on a hunt for transcription factors that specifically regulate the expression of known cilia genes in mouse embryonic development. They identified the transcription factors SP5 and SP8 as key regulators for a large proportion of cilia genes, either directly or via other downstream transcriptional regulators, across multiple cell types. In the mouse embryo, SP5 and SP8 are exclusively expressed in ciliated cell types and induced expression of SP8 in non-ciliated cells was sufficient to increase the expression of cilia genes and induce some formation of primary cilia. Conversely, lack of SP5 and SP8 resulted in reduced cilia formation, reduced cilia length and reduced expression of cilia genes in ciliated cell types.

In the subcellular resource of the HPA, SP5 and SP8 localizes to the nucleus of human cell lines. Their expression in ciliated versus non-ciliated cells, and their potential role in regulating the expression of cilia genes, remain to be explored.