Possible role of HmInx2 during development of the central nervous system of the medicinal leech (Hirudo medicinalis)

Abstract

There is broad gap junctional (GJ) coupling among cells of the Central Nervous System (CNS) during early neurogenesis in the medicinal leech (Hirudo medicinalis). To assay potential roles of the expression of a specific GJ protein of the leech Innexin family, two techniques to block the formation of GJs at early stages of development were tested: (1) knock-down of expression by using RNA interference intracellularly, and (2) blocking assembly of GJs extracellularly with mimetic peptides. The work reported here focused on HmInx2, which has been reported to be expressed exclusively in glial cells, particularly during gangliogenesis as well as later stages of central nervous system (CNS) development. siRNA was delivered on gold particles by means of biolistics (gene gun), while mimetic peptides were delivered via extracellular microinjection. Initial results suggest that HmInx2 is involved in interactions, possibly adhesive, between the macroglia (packet and neuropil glia) that give rise to ganglionic structure, since neurons appear disorganized and displaced following siRNA intervention. The effects of mimetic peptide injection are similar but subtler, indicating that formation of HmInx2-based GJs is only partially affected by this extracellular reagent. These observations are consistent with the hypothesis that GJs between cellular elements of the CNS are necessary in early development for attaining and maintaining structural integrity. GJ-mediated adhesion is proposed to play an important role in early neural development in the medicinal leech, as it does in mammalian nervous systems.