Synaptic patterning by morphogen signaling

Beadex, the Drosophila LIM only protein, is required for the growth of the larval neuromuscular junction

The appropriate growth of the neurons, accurate organization of their synapses, and successful neurotransmission are indispensable for sensorimotor activities. These processes are highly dynamic and tightly regulated. Extensive genetic, molecular, physiological, and behavioral studies have identified many molecular candidates and investigated their roles in various neuromuscular processes. In this article, we show that Beadex (Bx), the Drosophila LIM only (LMO) protein, is required for motor activities and neuromuscular growth of Drosophila. The larvae bearing Bx7, a null allele of Bx, and the RNAi-mediated neuronal-specific knockdown of Bx show drastically reduced crawling behavior, a diminished synaptic span of the neuromuscular junctions (NMJs) and an increased spontaneous neuronal firing with altered motor patterns in the central pattern generators (CPGs). Microarray studies identified multiple targets of Beadex that are involved in different cellular and molecular pathways, including those associated with the cytoskeleton and mitochondria that could be responsible for the observed neuromuscular defects. With genetic interaction studies, we further show that Highwire (Hiw), a negative regulator of synaptic growth at the NMJs, negatively regulates Bx, as the latter's deficiency was able to rescue the phenotype of the Hiw null mutant, HiwDN. Thus, our data indicate that Beadex functions downstream of Hiw to regulate the larval synaptic growth and physiology.NEW & NOTEWORTHY A novel role for Beadex (Bx) regulates the larval neuromuscular junction (NMJ) structure and function in a tissue-specific manner. Bx is expressed in a subset of Toll-6-expressing neurons and is involved in regulating synaptic span and physiology, possibly through its negative interaction with Highwire (Hiw). The findings of this study provide insights into the molecular mechanisms underlying NMJ development and function and warrant further investigation to understand the role of Bx in these processes fully.

Communicating by touch--neurons are not alone

Long-distance cell-cell communication is essential for organ development and function. Whereas neurons communicate at long distances by transferring signals at sites of direct contact (i.e., at synapses), it has been presumed that the only way other cell types signal is by dispersing signals through extracellular fluid--indirectly. Recent evidence from Drosophila suggests that non-neuronal cells also exchange signaling proteins at sites of direct contact, even when long distances separate the cells. We review here contact-mediated signaling in neurons and discuss how this signaling mechanism is shared by other cell types.

The best-laid plans go oft awry: synaptogenic growth factor signaling in neuropsychiatric disease

Growth factors play important roles in synapse formation. Mouse models of neuropsychiatric diseases suggest that defects in synaptogenic growth factors, their receptors, and signaling pathways can lead to disordered neural development and various behavioral phenotypes, including anxiety, memory problems, and social deficits. Genetic association studies in humans have found evidence for similar relationships between growth factor signaling pathways and neuropsychiatric phenotypes. Accumulating data suggest that dysfunction in neuronal circuitry, caused by defects in growth factor-mediated synapse formation, contributes to the susceptibility to multiple neuropsychiatric diseases, including epilepsy, autism, and disorders of thought and mood (e.g., schizophrenia and bipolar disorder, respectively). In this review, we will focus on how specific synaptogenic growth factors and their downstream signaling pathways might be involved in the development of neuropsychiatric diseases.