CHANGES IN THE PROPERTIES OF GAP-JUNCTIONS DURING NEURONAL DIFFERENTIATION OF HIPPOCAMPAL PROGENITOR CELLS

The cellular mechanisms that regulate progenitor cell lineage elaborat ion and maturation during embryonic development of the mammalian brain are poorly understood, Conditionally immortalized mouse hippocampal m ultipotent progenitor cells (MK31 cells) were found to be strongly cou pled by gap junctions comprising connexin 43 (Cx43) during early neuro nal ontogeny; the presence of this Cx type was confirmed by electrophy siological, molecular biological, and immunocytochemical assays. Howev er, as progenitor cells underwent intermediate stages of neuronal diff erentiation under the influence of interleukin 7 (IL-7) alone or termi nal differentiation after composite exposure to basic fibroblast growt h factor, IL-7, and transforming growth factor a, coupling strength an d the level of Cx43 expression declined, An additional population of j unctional channels with distinct properties was detected at an interme diate stage of neuronal differentiation. Reverse transcription-PCR ass ays detected mRNA encoding Cx40 in IL-7-treated cells and Cx33 after b oth treatment conditions. Because functional channels in exogenous exp ression systems are not formed by pairing Cx40 with Cx43 or by pairing Cx33 with itself or additional connexins, these experimental observat ions raise the possibility that the progressive loss of coupling durin g differentiation of neural progenitor cells may involve downregulatio n of Cx43 coupled with potentiation of expression of Cx33 and Cx40. Fu rthermore, continued expression of Cx43 in differentiating neuroblasts could mediate intercellular communication between neuronal precursor cells and astrocytes by direct signaling via homotypic gap junction ch annels.