Effect of AVT antisense oligodeoxynucleotides on AVT release induced by hypertonic stimulation in chicks

TonEBP regulates hyperosmolality-induced arginine vasotocin gene expression in the chick (Gallus domesticus)

Arginine vasotocin (AVT) is expressed mainly in the paraventircular and supraoptic nuclei of the hypothalamus in chicken. This peptide is known to act as an antidiuretic hormone and its gene expression is stimulated by hyperosmolality. However, the transcription factors that regulate the AVT gene expression induced by hyperosmolality are still unknown. In this study, we examined the role of hyper-tonicity enhancer binding protein (TonEBP) in the transcriptional regulation of AVT gene in chicken. TonEBP mRNA expression levels increased at 1h after salt-loading treatment in the hypothalamus. This increase preceded that in AVT and c-fos mRNA expression. Intracerebroventricular injections of TonEBP antisense oligonucleotides, before the salt-loading treatment, prevented the increase in AVT gene expression. These results, all together, suggest that the transcription factor TonEBP may be involved in the regulation of AVT genes expression in response to a hyperosmotic environment in chicken.

Effect of hyperosmotic stimulation on aquaporins gene expression in chick kidney

Birds can produce hyperosmotic urine, but their renal morphology differs from that of mammals. Recent studies in mammals, suggested that various aquaporins (AQPs) are present in the kidney and play crucial roles in urine production. To elucidate the role of AQPs in the avian kidney, we first examined for the presence of AQP1, 2, 3, 4, 7 and 9 mRNAs in the chick (Gallus gallus) kidney by RT-PCR analysis. Next, we quantified variations of AQPs mRNAs levels in chick kidney after hyperosmotic stimulation (water-deprivation or salt-loading) by real-time RT-PCR analysis. Our study showed that in addition to AQP1, 2, 3, 4 and 7, chick kidney also expressed AQP9 and that hyperosmotic stimulation induced changes in AQPs expression. In particular, water-deprivation increased AQP2 and AQP3 mRNAs levels, whereas salt-loading induced a significant increase in AQP1, AQP2 and AQP9 mRNAs levels. AQP4 and AQP7 mRNA levels were not affected by any hyperosmotic stimulation. Taken together, these results indicated that the presence of AQPs in chick kidney is similar to that in mammals, that the chick kidney has an additional AQP9 and that AQP1, 2, 3 and 9 may play a crucial but different role in water permeability in this organ.