Functional Consequences of Necdin Nucleocytoplasmic Localization

Background: Necdin, a MAGE family protein expressed primarily in the nervous system, has been shown to interact with both nuclear and cytoplasmic proteins, but the mechanism of its nucleocytoplasmic transport are unknown. Methodology/Principal Findings: We carried out a large-scale interaction screen using necdin as a bait in the yeast RRS system, and found a wide range of potential interactors with different subcellular localizations, including over 60 new candidates for direct binding to necdin. Integration of these interactions into a comprehensive network revealed a number of coherent interaction modules, including a cytoplasmic module connecting to necdin through huntingtin-associated protein 1 (Hap1), dynactin and hip-1 protein interactor (Hippi); a nuclear P53 and Creb-binding-protein (Crebbp) module, connecting through Crebbp and WW domain-containing transcription regulator protein 1 (Wwtr1); and a nucleocytoplasmic transport module, connecting through transportins 1 and 2. We validated the necdin-transportin1 interaction and characterized a sequence motif in necdin that modulates karyopherin interaction. Surprisingly, a D234P necdin mutant showed enhanced binding to both transportin1 and importin b1. Finally, exclusion of necdin from the nucleus triggered extensive cell death. Conclusions/Significance: These data suggest that necdin has multiple roles within protein complexes in different subcellular compartments, and indicate that it can utilize multiple karyopherin-dependent pathways to modulate its localization

Necdin Protects Embryonic Motoneurons from Programmed Cell Death

NECDIN belongs to the type II Melanoma Associated Antigen Gene Expression gene family and is located in the Prader-Willi Syndrome (PWS) critical region. Necdin-deficient mice develop symptoms of PWS, including a sensory and motor deficit. However, the mechanisms underlying the motor deficit remain elusive. Here, we show that the genetic ablation of Necdin, whose expression is restricted to post-mitotic neurons in the spinal cord during development, leads to a loss of 31% of specified motoneurons. The increased neuronal loss occurs during the period of naturally-occurring cell death and is not confined to specific pools of motoneurons. To better understand the role of Necdin during the period of programmed cell death of motoneurons we used embryonic spinal cord explants and primary motoneuron cultures from Necdin-deficient mice. Interestingly, while Necdin-deficient motoneurons present the same survival response to neurotrophic factors, we demonstrate that deletion of Necdin leads to an increased susceptibility of motoneurons to neurotrophic factor deprivation. We show that by neutralizing TNFα this increased susceptibility of Necdin-deficient motoneurons to trophic factor deprivation can be reduced to the normal level. We propose that Necdin is implicated through the TNF-receptor 1 pathway in the developmental death of motoneurons

Postprandial cardiac autonomic function in Prader-Willi syndrome

Objective To measure, as indicators of cardiac autonomic function, postprandial heart rate variability (HRV) and arterial stiffness in adults with PWS. Methods Ten adults with PWS were compared with 11 matched healthy obese subjects and 9 healthy lean subjects. Electrocardiographic traces and arterial stiffness were recorded over a period of 10 minutes at −60, 0, 30, 60, 120 and 240 minutes after consumption of a standardized 600-kCal breakfast. Frequency domain analysis was performed using fast Fourier transform to estimate power spectral density in the full spectrum and in low-frequency (LF 0·04–0·15 Hz) and high-frequency (HF 0·15–0·40 Hz) bands. Results ANCOVA revealed a reduced LF HRV meal response in adults with PWS compared with obese controls, with no differences in HF HRV, LF/HF ratio, heart rate, total power or arterial stiffness meal responses. Conclusions This study assessed cardiac autonomic function in adults with PWS compared with matched obese and lean subjects in response to a meal. Results suggest impaired postprandial ANS responsiveness in PWS, which could contribute to both the known increased cardiovascular risk and obesity