Metal ion stimulators of PDE5 cause similar conformational changes in the enzyme as does cGMP or sildenafil

Purified PDE5 preparations exhibited variable proportions of two mobility forms (Bands 2 and 3) by native PAGE. Treatment of recombinant or native PDE5 with either cGMP or a substrate analog such as sildenafil, each of which is known to produce stimulatory effects on enzyme functions, caused a similar native PAGE band-shift to the lower mobility form (shift of Band 2 to Band 3). Incubation of PDE5 with Mg⁺⁺ or Mn⁺⁺, which is known to stimulate activity, caused a similar shift of the enzyme from Band 2 to Band 3 as did cGMP or sildenafil, but incubation with EDTA caused a time- and concentration-dependent shift to higher mobility (shift of Bands 2 and 3 to Band 1). A slow time course of the EDTA-induced band-shift suggested removal of a pre-bound metal ion (Me⁺⁺) with affinity of ~ 0.1 nM, which was similar to the previously determined affinity of PDE5 for Zn⁺⁺. The EDTA-treated enzyme (Band 1) could be shifted to Bands 2 and 3 by addition of cGMP, sildenafil, or Me⁺⁺; however, the cGMP- or sildenafil-induced shift was inhibited and the Me⁺⁺-induced shift was facilitated by treatment with EDTA. Results suggested that Me⁺⁺ removal from PDE5 produces a unique apoenzyme form (Band 1, more globular, negatively charged, or both) of PDE5 that can be partially converted to forms (Band 2, less globular or negatively charged, or both; and Band 3, more elongated/positively charged, or both) by addition of Me⁺⁺, substrate, or substrate analog. It is concluded that Me⁺⁺ causes conversion of PDE5 to similar conformational forms as caused by substrate or inhibitor binding to the catalytic site.     

Cryptic organisation within an apparently irregular rostrocaudal distribution of interneurons in the embryonic zebrafish spinal cord

The molecules and mechanisms involved in patterning the dorsoventral axis of the developing vertebrate spinal cord have been investigated extensively and many are well known. Conversely, knowledge of mechanisms patterning cellular distributions along the rostrocaudal axis is relatively more restricted. Much is known about the rostrocaudal distribution of motoneurons and spinal cord cells derived from neural crest but there is little known about the rostrocaudal patterning of most of the other spinal cord neurons. Here we report data from our analyses of the distribution of dorsal longitudinal ascending (DoLA) interneurons in the developing zebrafish spinal cord. We show that, although apparently distributed irregularly, these cells have cryptic organisation. We present a novel cell-labelling technique that reveals that DoLA interneurons migrate rostrally along the dorsal longitudinal fasciculus of the spinal cord during development. This cell-labelling strategy may be useful for in vivo analysis of factors controlling neuron migration in the central nervous system. Additionally, we show that DoLA interneurons persist in the developing spinal cord for longer than previously reported. These findings illustrate the need to investigate factors and mechanisms that determine “irregular” patterns of cell distribution, particularly in the central nervous system but also in other tissues of developing embryos.