As a step toward generating a fate map of identified neuron populations in the mammalian hindbrain, we assessed the contributions of individual rhombomeres to the vestibular nuclear complex, a major sensorimotor area that spans the entire rhombencephalon. Transgenic mice harboring either the lacZ or the enhanced green fluorescent protein reporter genes under the transcriptional control of rhombomere-specific Hoxa2 enhancer elements were used to visualize rhombomere-derived domains. We labeled functionally identifiable vestibular projection neuron groups retrogradely with conjugated dextran-amines at successive embryonic stages and obtained developmental fate maps through direct comparison with the rhombomere-derived domains in the same embryos. The fate maps show that each vestibular neuron group derives from a unique rostrocaudal domain that is relatively stable developmentally, suggesting that anteroposterior migration is not a major contributor to the rostrocaudal patterning of the vestibular system. Most of the groups are multisegmental in origin, and each rhombomere is fated to give rise to two or more vestibular projection neuron types, in a complex pattern that is not segmentally iterated. Comparison with studies in the chicken embryo shows that the rostrocaudal patterning of identified vestibular projection neuron groups is generally well conserved between avians and mammalians but that significant speciesspecific differences exist in the rostrocaudal limits of particular groups. This mammalian hindbrain fate map can be used as the basis for targeting genetic manipulation to specific subpopulations of vestibular projection neurons.

We have studied the axonal projection patterns of commissural interneurons (CINs) in the neonatal rat spinal cord. Some CINs are integral components of the neuronal networks in the vertebrate spinal cord that generate locomotor activity. By using differential retrograde labeling protocols with fluorescent dextran amines, we show that CINs with ascending axons (ascending CINs, or aCINs) and CINs with descending axons (descending CINs, or dCINs) constitute largely different populations. We show that aCINs and dCINs occupy partially overlapping domains in the transverse plane. The aCINs are located at the dorsal margin, within the dorsal horn, centrally within the intermediate zone, and in the medial region of the ventral horn, whereas the dCINs are located predominantly among the ventral and central aCINs and in smaller numbers within the dorsal horn. The labeled aCINs and dCINs project for at least one and a half segment rostrally or caudally and are present in roughly equal numbers. We also demonstrate the presence of a third, smaller population of CINs whose axons bifurcate to project for at least one and a half segment both rostrally and caudally (adCINs). The adCINs are located predominantly among the central and ventral groups of aCINs and dCINs. Finally, we demonstrate the presence of CINs with axons projecting for fewer than one and a half segment in either direction. These "short-range CINs" are intermingled with the aCINs, dCINs, and adCINs. Our results provide an anatomical framework for further electrophysiological studies aimed at identifying the CINs that participate in the mammalian locomotor central pattern generator.

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BackgroundGlioblastomas are invasive therapy resistant brain tumors with extremely poor prognosis. The Glioma initiating cell (GIC) population contributes to therapeutic resistance and tumor recurrence. Targeting GIC-associated gene candidates could significantly impact GBM tumorigenicity. Here, we investigate a protein kinase, PBK/TOPK as a candidate for regulating growth, survival and in vivo tumorigenicity of GICs.MethodsPBK is highly upregulated in GICs and GBM tissues as shown by RNA and protein analyses. We knocked down PBK using shRNA vectors and inhibited the function of PBK protein with a pharmacological PBK inhibitor, HITOPK-032. We assessed viability, tumorsphere formation and apoptosis in three patient derived GIC cultures.ResultsGene knockdown of PBK led to decreased viability and sphere formation and in one culture an increase in apoptosis. Treatment of cells with inhibitor HITOPK-032 (5 μM and 10 μM) almost completely abolished growth and elicited a large increase in apoptosis in all three cultures. HI-TOPK-032 treatment (5 mg/kg and 10 mg/kg bodyweight) in vivo resulted in diminished growth of experimentally induced subcutaneous GBM tumors in mice. We also carried out multi-culture assays of cell survival to investigate the relative effects on GICs compared with the normal neural stem cells (NSCs) and their differentiated counterparts. Normal NSCs seemed to withstand treatment slightly better than the GICs.ConclusionOur study of identification and functional validation of PBK suggests that this candidate can be a promising molecular target for GBM treatment.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-015-0398-x) contains supplementary material, which is available to authorized users.