The hippocampus is divided into dorsal and ventral zones along its principal axis. The dorsal hippocampus is critical for learning and memory, yet the basic function of the ventral hippocampus remains elusive. Here we genetically manipulate a subset of excitatory neurons expressing the serotonin receptor 2c (Htr2c) in the ventral hippocampus. Genetically modified virus tracing reveals that these Htr2c cells establish monosynaptic excitatory connections with newly identified neurons in the Edinger-Westphal nucleus (EW), which directly innervate the medial prefrontal cortex. Inactivation of Htr2c cells impairs behavioral performance in a visual-detection task that demands attention, without affecting novel-object recognition, learning, or memory. This attention deficit was recapitulated by inhibition of EW cells and rescued by activation of EW cells or synaptic projections from Htr2c cells onto EW cells. This study uncovers a synaptic pathway for control of attention.
Synthetic viruses provide a powerful platform to delve deeper into the nature and function of viruses as well as to engineer viruses with novel properties. So far, most synthetic viruses have been RNA viruses (<30 kb) and small DNA viruses, such as bacteriophage phiX174. Baculoviruses contain a large circular dsDNA genome of 80-180 kb and have been used as biocontrol agents and protein expression vectors. Here, we report on the first synthesis of a baculovirus based on the type species Autographa californica nucleopolyhedrovirus, AcMNPV, by a combination of PCR and transformation-associated recombination in yeast. The synthetic genome, designated AcMNPV-WIV-Syn1, is 145 299 bp comprising the complete genome of AcMNPV except for the hr4a locus that was replaced with an ∼11.5 kb cassette of bacterial and yeast artificial chromosomal elements and an egfp gene. Sf9 insect cells were transfected with AcMNPV-WIV-Syn1 DNA and progeny virus was examined by electron microscopy, and assayed in one-step growth curves and oral infectivity. The results conclusively showed that the rescued virus AcMNPV-WIV-Syn1 had structural and biological properties comparable to the parental virus. We validated a proof of concept that a bona fide baculovirus can be synthesized. The new platform allows manipulation at any or multiple loci and will facilitate future studies such as identifying the minimal baculovirus genome and construction of better expression vectors. This is the largest DNA virus synthesized so far, and its success is likely to be the impetus to stimulate the fields of other large DNA viruses such as herpesviruses and poxviruses.
Cholinergic system is very important for many higher brain functions, including learning and memory. Cholinergic neurons, especially those in the basal forebrain, are specifically susceptible in some neurodegenerative diseases, such as in Alzheimer's disease (AD). Here, we studied the cholinergic system lesion effects of five familial AD mutations in 5XFAD mice, a transgenic mouse model of AD. Although the cholinergic system has been studied in this mouse model, the cholinergic deficits in AD mice have never been systematically mapped in a whole-brain three-dimensional (3D) reconstruction. Using the 3D reconstruction technology combined with immunohistochemistry (3D-IHC) and design-based stereology, we comprehensively compared the differences of the cholinergic neurons and fibers between the 5XFAD mice and C57BL/6 control mice at different age. Here, we found that the lesion of cholinergic fibers occurred earlier than the cholinergic neuron loss in 5XFAD mice. The cholinergic fiber lesions in the AD mice started sequentially in amygdala, cortex, hippocampus, and then basal forebrain. However, the basal forebrain was the first brain region observed with cholinergic neuron loss at the age of 9 months in 5XFAD mice, whereas such phenomenon first occurred at the age of 15 months in C57BL/6 control mice. Moreover, using 3D reconstruction to compare the lesion of cholinergic system of aged 5XFAD and C57BL/6 control mice, it is intuitive to notice the pathologic regions and severity of lesion. Therefore, the 3D-IHC provides detailed overview of the cholinergic neurons in the whole mouse brain, which will contribute to the study of the developing and pathologic mouse brain.
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