Acetylcholine receptor ɛ-subunit deletion causes muscle weakness and atrophy in juvenile and adult mice

In mammalian muscle a postnatal switch in functional properties of neuromuscular transmission occurs when miniature end plate currents become shorter and the conductance and Ca2+ permeability of end plate channels increases. These changes are due to replacement during early neonatal development of the γ-subunit of the fetal acetylcholine receptor (AChR) by the ɛ-subunit. The long-term functional consequences of this switch for neuromuscular transmission and motor behavior of the animal remained elusive. We report that deletion of the ɛ-subunit gene caused in homozygous mutant mice the persistence of γ-subunit gene expression in juvenile and adult animals. Neuromuscular transmission in these animals is based on fetal type AChRs present in the end plate at reduced density. Impaired neuromuscular transmission, progressive muscle weakness, and atrophy caused premature death 2 to 3 months after birth. The results demonstrate that postnatal incorporation into the end plate of ɛ-subunit containing AChRs is essential for normal development of skeletal muscle.

Recovery of Diadema antillarum reduces macroalgal cover and increases abundance of juvenile corals on a Caribbean reef

The transition of many Caribbean reefs from coral to macroalgal dominance has been a prominent issue in coral reef ecology for more than 20 years. Alternative stable state theory predicts that these changes are reversible but, to date, there is little indication of this having occurred. Here we present evidence of the initiation of such a reversal in Jamaica, where shallow reefs at five sites along 8 km of coastline now are characterized by a sea urchin-grazed zone with a mean width of 60 m. In comparison to the seaward algal zone, macroalgae are rare in the urchin zone, where the density of Diadema antillarum is 10 times higher and the density of juvenile corals is up to 11 times higher. These densities are close to those recorded in the late 1970s and early 1980s and are in striking contrast to the decade-long recruitment failure for both Diadema and scleractinians. If these trends continue and expand spatially, reefs throughout the Caribbean may again become dominated by corals and algal turf.