Evidence for a Conserved Function in Synapse Formation Reveals Phr1 as a Candidate Gene for Respiratory Failure in Newborn Mice

Abstract

Genetic studies using a set of overlapping deletions centered at the piebald locus on distal mouse chromosome 14 have defined a genomic region associated with respiratory distress and lethality at birth. We have isolated and characterized the candidate gene Phr1 that is located within the respiratory distress critical genomic interval. Phr1 is the ortholog of the human Protein Associated with Myc as well as Drosophila highwire and Caenorhabditis elegans regulator of presynaptic morphology 1. Phr1 is expressed in the embryonic and postnatal nervous system. In mice lacking Phr1, the phrenic nerve failed to completely innervate the diaphragm. In addition, nerve terminal morphology was severely disrupted, comparable with the synaptic defects seen in the Drosophila hiw and C. elegans rpm-1 mutants. Although intercostal muscles were completely innervated, they also showed dysmorphic nerve terminals. In addition, sensory neuron terminals in the diaphragm were abnormal. The neuromuscular junctions showed excessive sprouting of nerve terminals, consistent with inadequate presynaptic stimulation of the muscle. On the basis of the abnormal neuronal morphology seen in mice, Drosophila, and C. elegans, we propose that Phr1 plays a conserved role in synaptic development and is a candidate gene for respiratory distress and ventilatory disorders that arise from defective neuronal control of breathing.

The role of ubiquitylation in nerve cell development

“…Taken together, these finding are in nice accord with data obtained in C. elegans, further supporting the notion that Highwire/RPM-1 and FSN operate in the same pathway with DLK as a major target 122,125 . Even in mammals, the Highwire/RPM-1 and FSN orthologues, Phr1 and Fbxo45, seem to function in a complex at synapses 126,127 , but this complex may have neuronal targets other than DLK 128 .…”

Defining Minimal Binding Regions in Regulator of Presynaptic Morphology 1 (RPM-1) Using Caenorhabditis elegans Neurons Reveals Differential Signaling Complexes

“…The PHR proteins regulate various events in neuronal development, including synapse formation (3)(4)(5)(6), axon guidance (6 -9), and axon termination (7, 10 -13). In C. elegans, defects in neuronal development caused by loss of RPM-1 result in mild defects in locomotion and severe defects in short-term learning (14).…”

Motor Axon Guidance of the Mammalian Trochlear and Phrenic Nerves: Dependence on the Netrin ReceptorUnc5cand Modifier Loci

“…Neonatal respiratory distress and subsequent lethality can be associated with defects in innervation of the diaphragm and other respiratory muscles (Sanes and Lichtman, 2001;Burgess et al, 2004). To determine whether such defects occur in B6.Unc5c mutant mice, diaphragm innervation was analyzed in E18.5 mutant and littermate control embryos.…”

“…Unc5c riboprobes were generated as described previously (Ackerman et al, 1997). Serial sections through the cervical spinal cord of fresh-frozen E14.5 embryos were collected using a cryostat, and in situ hybridization was performed as described previously (Burgess et al, 2004). After hybridization, sections were incubated with peroxidaseconjugated anti-digoxygenin antibodies (1:2000; Roche Products, Welwyn Garden City, UK).…”