Expression of ZAKI-4 messenger ribonucleic acid in the brain during bat development and the effect of hypothyroidism

We identified ZAKI-4 (also designated as DSCR1L1) as a thyroid hormone resp onsive gene in cultured human skin fibroblasts. Recently it has been report ed that ZAKI-4 belongs to an evolutionary conserved family of proteins that function as calcineurin inhibitor. In human, ZAKI-4 and calcineurin are hi ghly expressed in brain, where thyroid hormones play essential roles in the development during fetal and neonatal periods. In the present study, we ex amined the temporal and spatial expression patterns of ZAKI-4 messenger RNA (mRNA) in control and hypothyroid rat brains. Northern blot analysis revea led that ZAKI-4 mRNA was detected in both cerebral cortex and cerebellum as early as embryonic day (E)18. In the cerebral cortex, the expression level gradually increased with age, reaching a plateau at postnatal day (P)7 and remained constant thereafter until P30. A similar pattern of increase with age was also observed in hypothyroid rats; however, the magnitude of the i ncrease was significantly reduced. In control rats, the fold increase in ZA KI-4 mRNA level from E18 to P17 was 10.8; whereas in hypothyroid rats, it w as 7.4. in cerebellum the expression level did not change with age or by th yroid status. In situ hybridization revealed that ZAKI-4 mRNA is widely exp ressed in neurons throughout the brain. It is noteworthy that the expressio n in the neurons of layer VI of the cerebral cortex was more evident in con trol rats than that in hypothyroid rats from P17 to P30. Though not influen ced by hypothyroidism, there were several regions of the brain in which ZAK I-4 mRNA was strongly expressed. These regions were the mitral cell layer o f the olfactory bulb, the substantia nigra, and the kippocampus, where calc ineurin is also abundantly expressed. Therefore, it may be hypothesized tha t ZAKI-4 plays an important role in the development and function of the bra in by modulating calcineurin function; and decrease in ZAKI-4 mRNA expressi on in the specific brain areas may explain, in some parts, the mechanism of abnormal brain development by hypothyroidism.