Phyhd1, an XPhyH-like homologue, is induced in mouse T cells upon T cell stimulation

We previously identified XPhyH-like as a gene whose expression is enhanced in Xenopus blood cells during the refractory period, in which Xenopus tadpoles transiently lose their tail regenerative ability. Although we hypothesized that some autoreactive immune cells attack tail blastemal cells during the refractory period and XPhyH-like expressing immune cells were involved in the process, the nature of cells expressing XPhyH-like remain unknown, partly due to the lack of leukocyte markers available in Xenopus. In the present study, we used mice to analyze the expression pattern of XPhyH-like homologues. When we used quantitative reverse transcription-polymerase chain reaction (RT--PCR) to analyze the expression of mouse Phyhd1, an XPhyH-like orthologue, and Phyh, a Phyhd1 paralogue, both Phyhd1 and Phyh showed similar tissue-specific expression patterns. The expression pattern in leukocytes, however, differed between Phyhd1 and Phyh; Phyhd1 was considerably expressed in T cells and B cells. Moreover, the expression of Phyhd1 in T cells was up-regulated for approximately 3- to 7-times by T cell stimulation 3-4 days after the stimulation, unlike Phyh. Our findings suggest that Phyhd1 and Phyh have distinct roles in mouse leukocytes and Phyhd1 is related to T cell differentiation and/or function of effector T cells.