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Semaphorin 3A (Sema3A), a secretory semaphorin, exerts various biological actions through a complex between neuropilin-1 and plexinAs (PlexAs). Sema3A induces retrograde signaling, which is involved in regulating dendritic localization of GluA2 (also known as GRIA2), an AMPA receptor subunit. Here, we investigated a possible interaction between retrograde signaling pathways for Sema3A and nerve growth factor (NGF). Sema3A induces colocalization of PlexA4 (also known as PLXNA4) signals with those of tropomyosin-related kinase A (TrkA, also known as NTRK1) in growth cones, and these colocalized signals were then observed along the axons. The timelapse imaging of PlexA4 and several TrkA mutants showed that the kinase and dynein-binding activity of TrkA were required for Sema3A-induced retrograde transport of the PlexA4-TrkA complex along the axons. The inhibition of the phosphoinositide 3-kinase (PI3K)-Akt signal, a downstream signaling pathway of TrkA, in the distal axon suppressed Sema3A-induced dendritic localization of GluA2. The knockdown of TrkA suppressed Sema3A-induced dendritic localization of GluA2 and that suppressed Sema3A-regulated dendritic branching both in vitro and in vivo. These findings suggest that by interacting with PlexA4, TrkA plays a crucial role in redirecting local Sema3A signaling to retrograde axonal transport, thereby regulating dendritic GluA2 localization and patterning.

Noncompaction of the left ventricular myocardium (NCLV) is an uncommon congenital cardiomyopathy with poor prognosis. We describe a case of NCLV that developed in a pregnant woman and her neonate. A nulliparous woman was referred at 24 weeks' gestation due to dyspnea and fetal hydrops. Maternal echocardiography demonstrated NCLV with characteristic findings of prominent and excessive ventricular trabeculations and deep intertrabecular recesses in the left ventricle. An M-mode echocardiography suggested depressed left ventricular systolic function. A fetal echocardiography at 24 weeks' gestation demonstrated cardiomegaly, but morphologic findings were not definitive for NCLV. An emergency cesarean section was performed due to maternal heart failure. A neonatal echocardiography diagnosed NCLV with depressed left ventricular systolic function. The neonate died of cardiac failure on the second day of life. Autopsy confirmed the echocardiographic findings. Since patients with NCLV may develop heart failure, multidisciplinary management is mandatory. In addition, awareness of familial occurrence of NCLV should be kept in mind for early diagnosis in the fetus and neonate.

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