ATBF1-A protein, but not ATBF1-B, is preferentially expressed in developing rat brain

The ATBF1 gene encodes transcription factors containing four homeodomains and multiple zinc finger motifs. However, the gene products have yet to be identified and the role remains unknown in vivo. In this study, we raised an antiserum for ATBF1 and found high levels of expression of ATBF1 in developing rat brain. Western and Northern blot analyses detected a 400 kDa protein and 12.5 kb mRNA in developing rat brain, respectively; both corresponding to ATBF1-A but not the B isoform. The protein was highly expressed in the midbrain and diencephalon and mRNA was highly expressed in the brainstem, mostly in embryo and neonatal brain. Immunohistochemistry identified postmitotic neurons in the brainstem as the major site of ATBF1 expression, and the expression levels varied depending on age of and location in the brain. Expression was transient and weak in the precursor cells at early neurogenesis. ATBF1 decreased postnatally, but remained in mature neurons, including those expressing DOPA decarboxylase (DDC). High levels of ATBF1 were expressed in precursor cells in accordance with neurogenesis and were continued to the mature neurons in specific areas such as the inferior colliculus. Expression was not significant from precursor cells to mature neurons in the cerebral cortex and hippocampus. ATBF1 and its Drosophila homolog, Zfh-2, are known to regulate cell differentiation and proliferation via the interaction with either of the basic helix-loop-helix transcription factors, c-myb, or the DDC gene. Together with these reported functions the expression features detected here suggest that investigating the protein expression of ZFH-4 in developing brain to further our understanding of the role of this group of transcription factors. In conclusion, the current study detected mature ATBF1-A protein of 404 kDa, but not ATBF1-B, and characterized its age- and region-specific expression in developing rat brain. The protein was expressed in both immature precursor cells and postmitotic neurons in a regionally defined manner. Although the molecules reported to interact with ATBF1 are still limited in the CNS, our data suggest that ATBF1 could be a regulator of neuronal cell development through interaction with c-Myb, DDC, and, importantly, with bHLH transcription factors. The information provided here is useful for future research aimed at clarifying the function of ATBF1. In addition, future morphologic and biochemical studies in vivo as well as in vitro should benefit from the availability of the anti-ATBF1 antiserum we generated.