The midbrain-hindbrain boundary (MHB) is a long-lasting organizing center in the vertebrate neural tube that is both necessary and sufficient for the ordered development of midbrain and anterior hindbrain (midbrain-hindbrain domain, MH). The MHB also coincides with a pool of progenitor cells that contributes neurons to the entire MH. Here we show that the organizing activity and progenitor state of the MHB are co-regulated by a single microRNA, miR-9, during late embryonic development in zebrafish. Endogenous miR-9 expression, initiated at late stages, selectively spares the MHB. Gain- and loss-of-function studies, in silico predictions and sensor assays in vivo demonstrate that miR-9 targets several components of the Fgf signaling pathway, thereby delimiting the organizing activity of the MHB. In addition, miR-9 promotes progression of neurogenesis in the MH, defining the MHB progenitor pool. Together, these findings highlight a previously unknown mechanism by which a single microRNA fine-tunes late MHB coherence via its co-regulation of patterning activities and neurogenesis.

The chick midbrain is subdivided into functionally distinct ventral and dorsal domains, tegmentum and optic tectum. In the mature tectum, neurons are organized in layers, while they form discrete nuclei in the tegmentum. Dorsoventral (DV) specification of the early midbrain should thus play a crucial role for the organization of the neuronal circuitry in optic tectum and tegmentum. To investigate regional commitment and establishment of cellular differences along the midbrain DV axis, we examined

BackgroundMiR-9 is a small non-coding RNA that is highly conserved between species and primarily expressed in the central nervous system (CNS). It is known to influence proliferation and neuronal differentiation in the brain and spinal cord of different vertebrates. Different studies have pointed to regional and species-specific differences in the response of neural progenitors to miR-9.MethodsIn ovo and ex ovo electroporation was used to overexpress or reduce miR-9 followed by mRNA in situ hybridisation and immunofluorescent stainings to evaluate miR- expression and the effect of changed miR-9 expression.ResultsWe have investigated the expression and function of miR-9 during early development of the mid-hindbrain region (MH) in chick. Our analysis reveals a closer relationship of chick miR-9 to mammalian miR-9 than to fish and a dynamic expression pattern in the chick neural tube. Early in development, miR-9 is diffusely expressed in the entire brain, bar the forebrain, and it becomes more restricted to specific areas of the CNS at later stages. MiR-9 overexpression at HH9–10 results in a reduction of FGF8 expression and premature neuronal differentiation in the mid-hindbrain boundary (MHB). Within the midbrain miR-9 does not cause premature neuronal differentiation it rather reduces proliferation in the midbrain.ConclusionOur findings indicate that miR-9 has regional specific effects in the developing mid-hindbrain region with a divergence of response of regional progenitors.Electronic supplementary materialThe online version of this article (10.1186/s12861-017-0159-8) contains supplementary material, which is available to authorized users.

Background: The autosomal dominant form of Emery-Dreifuss muscular dystrophy (AD-EDMD) is caused by mutations in the gene encoding for the lamins A and C (LMNA). Lamins are intermediate filament proteins which form the nuclear lamina underlying the inner nuclear membrane. We have studied the expression and the localization of nuclear envelope proteins in three different cell types and muscle tissue of an AD-EDMD patient carrying a point mutation R377H in the lamin A/C gene.

Dopamine-producing neurons in the mammalian midbrain have received considerable attention in recent years because of their involvement in diverse neurological and psychiatric human disorders such as Parkinson's Disease (PD), schizophrenia and addiction. Although the underlying pathogenic mechanisms of these disorders are far from being understood, it is meanwhile accepted that a combination of genetic predisposition and environmental factors lead to the disease state. More recent evidence also suggests that both neurological and psychiatric disorders result from early disturbances affecting the normal development of the mesencephalic dopaminergic (mesDA) neurons. Understanding the cues directing the generation of the different mesDA cell groups, the establishment of their proper connections within the brain and their maintenance in the adult are therefore also of great clinical interest. Rodents, and in particular the mouse, have served as the classical "surrogate" organism for these studies based on their phylogenetic relationship to humans, their relatively well characterized mesDA system on both the anatomical and physiological levels, and especially on the propensity of the mouse to genetic manipulation enabling the dissection of genetic pathways underlying the proper generation and maintenance of the mesDA system in this species. In the present review, we will summarize recent findings in the overall context of murine mesDA neuron development.

expressed in the floor plate and we show that it is necessary and sufficient for the development of dopamine neurons, in embryonic midbrain progenitors and embryonic stem cells.Foxa2 continues to be expressed in dopamine neurons in the adult mouse brain. In old, foxa2-heterozygous, mutant mice, we observe the spontaneous appearance of motor deficits; this movement disorder is accompanied by a loss of dopamine neurons. A loss of dopamine neurons is characteristic of Parkinson's Disease (PD) and additional features of the dopamine neuron loss in mutant mice are reminiscent of PD. This is the first mouse model of spontaneous, age-dependent dopamine neuron degeneration.Targeting the survival function of the foxa2 gene may prove important in stem cell-based and pharmacological approaches to dopamine neuron disease. Stem cell biology, embryology, and this animal model of PD suggest that foxa2 is a critical gene during multiple windows of the ''molecular biography'' of the dopamine neuron. Our results suggest that the stem cell approach can shed valuable insights, not only in the realm of developmental biology, but, also, into the mechanisms of human degenerative disease.

Mesodiencephalic dopaminergic (mdDA) neurons are located in the ventral mesencephalon and caudal diencephalon of all tetrapod species studied so far. They are the most prominent DA neuronal population and are implicated in control and modulation of motor, cognitive and rewarding/affective behaviors. Their degeneration or dysfunction is intimately linked to several neurological and neuropsychiatric human diseases. To gain further insights into their generation, we studied spatiotemporal expression patterns and epistatic interactions in chick embryos of selected marker genes and signaling pathways associated with mdDA neuron development in mouse. We detected striking differences in the expression patterns of the chick orthologs of the mouse mdDA marker genes Pitx3 and Aldh1a1, which suggests important differences between the species in the generation/generating of these cells. We also discovered that the sonic hedgehog signaling pathway is both necessary and sufficient for the induction of ectopic PITX3 expression in chick mesencephalon downstream of WNT9A-induced LMX1a transcription. These aspects of early chicken development resemble the ontogeny of zebrafish diencephalic DA neuronal populations, and suggest a divergence between birds and mammals during evolution.

Poster abstracts / Int. J. Devl Neuroscience 24 (2006) 495-603 585 response depends mostly on OPL-derived signals and not brain signals. We cross-bred WBC mice with mice knock-out for the Dlx5 homeogene, a model of lack of olfactory innervation. Grafting of Dlx5 mutant OPL onto WT slice cultures indicates that the connectivity defect is primarily axonal. Conversely, grafting of a Dlx5 mutant OB in WT newborn animals resulted in OB innervation, suggests that the mutant OB is able to accept incoming neurites.We show that in Dlx5 mutant embryos WBC responsive cells are nearly absent, as the expression of several Wnt mRNAs is reduced in the adjacent territory. At the same time, the basement membrane of the forebrain fails to be fenestrated and the formation of the OB nerve layer is prevented. The role of Wnt signalling in olfactory connectivity has been assayed by the use of purified DKK-1 or sFRP2, blockers of the WBC pathway, in slice cultures. Results will be presented.These data highlight the existence of a complex interplay between cell populations of different embryonic origins for the establishment of olfactory connections, in which Wnt signals play a key role.Dopamine-synthesizing (DA) neurons constitute a prominent neuronal population in the vertebrate brain as they are involved in the control and modulation of key cerebral functions. The mesencephalic dopaminergic (mesDA) neurons of the mouse arise from the ventral midbrain during embryonic development. In mouse there are several key factors identified which control their induction, specification, proliferation and differentiation, like Fgf8, Shh and Wnt1. Even though the mouse mesDA system is the best studied, the spatiotemporal development of this neuronal population is complex and not yet fully understood. This makes it important to investigate additional vertebrate models in terms of conserved developmental mechanisms. We performed for the first time a precise mapping of the expression patterns of the chicken orthologs for the mouse mesDA marker genes Aldh1a1, Nr4a2/Nurr1, Pitx3, Lmx1b, En1 and Th during early chicken development.With the in situ hybridisation technique on whole mount embryos or consecutive paraffin sections we investigated the mesDA marker genes at different developmental stages of the chicken embyro.We found striking differences in the spatiotemporal expression of some of these marker genes between the two species mouse and chicken, for example cAldh1a1 was not expressed at all in the developing ventral midbrain in chicken embryos. These differences may reflect partly different functions of the corresponding genes in birds and mammals that arose during evolution, whereas the similarities might show conserved pathways in the development of mesDA neurons. Spinocerebellar ataxia type 17 (SCA17) is a neurodegenerative disorder disease belonging to the autosomal dominant cerebellar ataxia (ADCA). SCA17 is caused by expansion of CAA/CAG trinucleotide repeats in the TATA box-binding protein (TBP) gene. It was proposed that the length ...