Identification and characterization of novel developmentally regulated neural-specific proteins, BRINP family

Processes of neuronal differentiation involve activation of a set of neuronal specific genes and cessation of cell proliferation in postmitotic neurons. Previous studies revealed that bone morphogenetic protein (BMP) and retinoic acid (RA) play important roles in the differentiation of peripheral sympathetic neurons such as the synergistic induction of responsiveness to specific neurotrophic factors. In the present study, while trying to clarify the mechanism of the BMP/RA-actions, we identified a novel neural-specific protein, BMP/RA-inducible neural-specific protein-1 (BRINP1) which shows no similarity to other known proteins. Subsequently, two homologous proteins, BRINP2 and BRINP3, making up the BRINP family, are identified. Individual BRINP genes have distinct regulatory mechanisms of expression within the nervous system. In rodent brain, BRINP1 is expressed from earlier developmental stage, i.e. E9.5, and widely expressed in various neuronal layers and nuclei of the adult animal, while BRINP2 and BRINP3 were detectable from E11.5 and expressed in rather limited regions in a complementary manner. During the course of perinatal development of sympathetic neurons, BRINP1 is induced from earlier embryonic stage and further increased toward adult stage, while BRINP3 expressed from earlier stage is replaced by BRINP2 expression which increases postnatally in accordance with the action of BMP2 and RA. Furthermore, when expressed in nonneuronal cells, all three BRINP family proteins suppressed the cell cycle progression. Possible physiological functions of BRINP family members in the development of the nervous system are discussed.