Identification of a novel type II activin receptor, type IIA-N, induced during the neural differentiation of murine P19 embryonal carcinoma cells

We have identified a novel type II activin receptor, called type IIA-N, the expression of which was induced during the neural differentiation of murine P19 embryonal carcinoma cells (P19 cells). P19 cells differentiate into several cell types dependent on the culture conditions. The induction of type IIA-N mRNA occurred predominantly in conjunction with neural differentiation. Sequence analysis of a cDNA clone for type IIA-N indicated that type IIA-N had a 24 bp insertion in the juxtamembrane region of the type IIA activin receptor suggesting that it is an alternative splicing product of the type IIA gene. Type IIA-N was also identified in human and Xenopus, and the amino acid sequences of three species were completely conserved. The expression of type IIA-N mRNA was specifically detected in neuroblastoma cells among several activin responsive cell lines. In vivo expression of type IIA-N mRNA was detected only in the neural tissues such as brain and spinal cord in adult mouse, by RT-PCR. Furthermore, its expression in developing Xenopus embryos was restricted to the neurula and later stages. These results suggest that the expression of type IIA-N is specific to neural cells and mediates neural differentiation-specific activin signaling.