Activating transcription factor 5 (ATF5) is a member of the ATF/cAMP response element-binding family of transcription factors, which compose a large group of basic region leucine zipper proteins whose members mediate diverse transcriptional regulatory functions. ATF5 has a well-established prosurvival activity and has been found to be overexpressed in several human cancers, in particular glioblastoma. However, the role(s) of ATF5 in development and normal physiology are unknown. Here we address this issue by deriving and characterizing homozygous Atf5 knockout mice. We find that Atf5(-/-) pups die neonatally, which, as explained below, is consistent with an olfactory defect resulting in a competitive suckling deficit. We show that Atf5 is highly expressed in olfactory sensory neurons (OSNs) in the main olfactory epithelium starting from embryonic stage 11.5 through adulthood. Immunostaining experiments with OSN-specific markers reveal that ATF5 is expressed in some immature OSNs and in all mature OSNs. Expression profiling and immunostaining experiments indicate that loss of Atf5 leads to a massive reduction in mature OSNs resulting from a differentiation defect and the induction of apoptosis. Ectopic expression of Atf5 in neural progenitor cells induces expression of multiple OSN-specific genes. Collectively, our results suggest a model in which Atf5 is first expressed in immature OSNs and the resultant ATF5 functions to promote differentiation into mature OSNs. Thus, ATF5 is required for terminal differentiation and survival of OSNs.
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