Cell interactions that affect axonogenesis in the leechTheromyzon rude

Abstract

The leech nervous system comprises a relatively simple network of longitudinal (connective) and transverse (segmental) nerves. We have followed the normal pattern of axon development in the glossiphoniid leech Theromyzon rude by immunostaining embryonic preparations with antibody to acetylated α-tubulin. The dependence of the normal pattern of axon growth on cells in the mesodermal (M) and ectodermal (N, O, P and Q)lineages was examined by selectively ablating subsets of these lineages in developing embryos. We found that ablating mesoderm severely disrupted overall axonogenesis, while various ectodermal ablations induced a range of more specific phenotypes. In particular, formation of the posterior segmental nerve(PP) was abnormal in embryos deficient in primary neuroectoderm (N lineage). More specific ablations demonstrated that a subset of N-derived cells were required for establishing the PP nerve root. Previous studies have shown that the PP nerve root is normally pioneered by an O lineage-derived neuron(PD). Our results suggest that the role of the N lineage-derived cells is to induce the migration of neuron PD to its normal position in the posterior compartment of the hemiganglion.

Intermediate filament genes as differentiation markers in the leech Helobdella

“…3). The onset of Hau-cif6 and Hau-cif7 expression was consistent with previous observations of neuronal morphological differentiation (Braun and Stent 1989; Shain et al 2004). Expression of Hau-cif6 and Hau-cif7 was first detected in a pair of cells within developing segmental ganglia during stage 9 (Fig.…”

“…3A, B). The location of the first pair of cells expressing Hau-cif6 and Hau-cif7 was similar to that of the first cell pair that undergoes axonogenesis in segmental ganglia of Theromyzon rude , another glossiphoniid leech (Shain et al 2004). Based on these observations, we concluded that Hau-if6 and Hau-if7 mark the differentiating and differentiated neurons.…”

ATP and NO dually control migration of microglia to nerve lesions

“…Cell migration is of course important not only in adults, but also early in the life of the organism (Shain et al, 2004). Although details of control of cell migration may vary from one motile cell type to another within a given animal, and even for the same cell type under different conditions, basic features of cell migration appear to be conserved across species, with various mechanisms proposed to account for directional sensing including models in which excitation and inhibition work in dual combination (e.g.…”

“…In this regard, it is significant that NO can play a major role in control of growth cone movement and motility (Tornieri et al, 2007; Welshhans et al, 2007). Whether some of the interactions between growth cones that influence their movement (Shain et al, 2004; Baker et al, 2007; Baker et al, 2008) are also important for guidance of microglial migration is unknown.…”

Confocal analysis of nervous system architecture in direct-developing juveniles of Neanthes arenaceodentata (Annelida, Nereididae)

“…Furthermore, based on arguments that Aciculata, a modern polychaete clade including Nereididae, is most closely related to stem annelids [7,8], the nereidid nervous system may be little changed from an early, errant polychaete ancestor. Despite advances made in understanding adult annelid nervous systems, exceedingly few studies focus on their nervous system development, the notable exception being studies on leech (e.g., [9-11]).…”