TMEM161B regulates cerebral cortical gyration, Sonic Hedgehog signaling, and ciliary structure in the developing central nervous system.

Sonic hedgehog signaling regulates processes of embryonic development across multiple tissues, yet factors regulating context-specific Shh signaling remain poorly understood. Exome sequencing of families with polymicrogyria (disordered cortical folding) revealed multiple individuals with biallelic deleterious variants in TMEM161B, which encodes a multi-pass transmembrane protein of unknown function. Tmem161b null mice demonstrated holoprosencephaly, craniofacial midline defects, eye defects, and spinal cord patterning changes consistent with impaired Shh signaling, but were without limb defects, suggesting a CNS-specific role of Tmem161b. Tmem161b depletion impaired the response to Smoothened activation in vitro and disrupted cortical histogenesis in vivo in both mouse and ferret models, including leading to abnormal gyration in the ferret model. Tmem161b localizes non-exclusively to the primary cilium, and scanning electron microscopy revealed shortened, dysmorphic, and ballooned ventricular zone cilia in the Tmem161b null mouse, suggesting that the Shh-related phenotypes may reflect ciliary dysfunction. Our data identify TMEM161B as a regulator of cerebral cortical gyration, as involved in primary ciliary structure, as a regulator of Shh signaling, and further implicate Shh signaling in human gyral development.

An optimized method for histological detection of dopaminergic neurons in Drosophila melanogaster.

Parkinson's disease (PD) affects >1 million Americans and is marked by the loss of dopaminergic neurons in the substantia nigra. PD has been linked to two causative factors: genetic risks (hereditary PD) and environmental toxins (idiopathic PD). In recent years, considerable effort has been devoted to the development of a Drosophila model of human PD that might be useful for examining the cellular mechanisms of PD pathology by genetic screening. In 2000, Feany and Bender reported a Drosophila model of PD in which transgenic flies expressing human mutant alpha-synuclein exhibited shortened life spans, dopaminergic losses, Parkinsonian behaviors, and Lewy bodies in surviving dopaminergic neurons. Since then, a number of studies have been published that validate the model or build on it; conversely, a number report an inability to replicate the results and suggest that most protocols for dopaminergic histology underreport the actual numbers of dopaminergic neurons in the insect brain. Here we report the optimization of dopaminergic histology in Drosophila and identification of new dopaminergic neurons, show the remarkable dendritic complexity of these neurons, and provide an updated count of these neurons in adult brains. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.

Zfh1, a somatic motor neuron transcription factor, regulates axon exit from the CNS.

Motor neurons are defined by their axon projections, which exit the CNS to innervate somatic or visceral musculature, yet remarkably little is known about how motor axons are programmed to exit the CNS. Here, we describe the role of the Drosophila Zfh1 transcription factor in promoting axon exit from the CNS. Zfh1 is detected in all embryonic somatic motor neurons, glia associated with the CNS surface and motor axons, and one identified interneuron. In zfh1 mutants, ventral projecting motor axons often stall at the edge of the CNS, failing to enter the muscle field, despite having normal motor neuron identity. Conversely, ectopic Zfh1 induces a subset of interneurons--all normally expressing two or more "ventral motor neuron transcription factors" (e.g. Islet, Hb9, Nkx6, Lim3)--to project laterally and exit the CNS. We conclude that Zfh1 is required for ventral motor axon exit from the CNS.

Combinatorial RNAi: a method for evaluating the functions of gene families in Drosophila.

Individual members of gene families often have partially redundant functions during nervous system development, making conventional genetic analysis problematic. Here we review experiments showing that several genes can be silenced together by injection of double-stranded RNAs into wild-type Drosophila embryos. By dye-labeling single neuroblasts in injected embryos, the effects of multigene silencing on individual CNS axon pathways can now be examined.