Flanking regulatory sequences of the locus encoding the murine GDNF receptor, c-ret, directs lac Z (beta-galactosidase) expression in developing somatosensory system

Tbx4 function during hindlimb development reveals a mechanism that explains the origins of proximal limb defects

We dissect genetically a gene regulatory network that involves the transcription factors Tbx4, Pitx1 and Isl1 acting cooperatively to establish the hindlimb bud, and identify key differences in the pathways that initiate formation of the hindlimb and forelimb. Using live image analysis of murine limb mesenchyme cells undergoing chondrogenesis in micromass culture, we distinguish a series of changes in cellular behaviours and cohesiveness that are required for chondrogenic precursors to undergo differentiation. Furthermore, we provide evidence that the proximal hindlimb defects observed in Tbx4 mutant mice result from a failure in the early differentiation step of chondroprogenitors into chondrocytes, providing an explanation for the origins of proximally biased limb defects.

Multipotent cell fate of neural crest-like cells derived from embryonic stem cells

Neural crest cells migrate throughout the embryo and differentiate into diverse derivatives: the peripheral neurons, cranial mesenchymal cells, and melanocytes. Because the neural crest cells have critical roles in organogenesis, detailed elucidation of neural crest cell differentiation is important in developmental biology. We recently reported that melanocytes could be induced from mouse ESCs. Here, we improved the culture system and showed the existence of neural crest-like precursors. The addition of retinoic acid to the culture medium reduced the hematopoiesis and promoted the expression of the neural crest marker genes. The colonies formed contained neural crest cell derivatives: neurons and glial cells, together with melanocytes. This suggested that neural crest-like cells assuming multiple cell fates had been generated in these present cultures. To isolate the neural crest-like cells, we analyzed the expression of c-Kit, a cell-surface protein expressed in the early stage of neural crest cells in vivo. The c-Kit-positive (c-Kit(+)) cells appeared as early as day 9 of the culture period and expressed the transcriptional factors Sox10 and Snail, which are expressed in neural crest cells. When the c-Kit(+) cells were separated from the cultures and recultured, they frequently formed colonies containing neurons, glial cells, and melanocytes. Even a single c-Kit(+) cell formed colonies that contained these three cell types, confirming their multipotential cell fate. The c-Kit(+) cells were also capable of migrating along neural crest migratory pathways in vivo. These results indicate that the c-Kit(+) cells isolated from melanocyte-differentiating cultures of ESCs are closely related to neural crest cells.

Phenotyping of sensory and sympathetic ganglion neurons of a galanin-overexpressing mouse--possible implications for pain processing

The distribution of galanin was studied in the lumbar 5 dorsal root ganglia (DRGs) and spinal cord, superior cervical ganglia (SCGs), and skin of transgenic mice overexpressing galanin under the dopamine beta-hydroxylase (DBH) promoter (GalOE-DBH mice) and in wild type (WT) mice. The DRGs and spinal cord were analysed before and after a unilateral, complete transection (axotomy) of the sciatic nerve and after dorsal rhizotomy. Both galanin protein and transcript were studied by, respectively, immunohistochemistry and in situ hybridization. Increased galanin expression was observed in several small, medium-sized and large DRG neuron profiles (NPs) in the naïve transgenic mouse, frequently in neurons lacking calcitonin gene-related peptide (CGRP) and isolectin B4-binding. This lack of coexistence was particularly evident in the medium-sized/large NPs. In the dorsal horn of the spinal cord, no differences were detected between GalOE-DBH and WT mice, both displaying a strong galanin-positive neuropil in the superficial laminae of the dorsal horn, but the transgenic mice showed a more abundant galanin-positive innervation of the ventral horn. A 12-day dorsal rhizotomy, surprisingly, failed to alter the galanin staining patterns in the dorsal (and ventral) dorsal horn. Unilateral axotomy induced upregulation of galanin in DRG NPs of all sizes in both types of mouse. In the hindpaw skin, a profuse galanin-positive fiber plexus was observed in sweat glands and around blood vessels of the transgenic mice, being much more restricted in WT mice. Finally, GalOE mice exhibited a strong galanin-like immunoreactivity in most SCG NPs. The overexpression of the peptide in DRGs and SCGs was paralleled by increased mRNA levels. The present results show that overexpression of galanin under the control of the DBH promoter does not only occur, as expected in these mice, in noradrenline/adrenaline neurons but also in DRG neurons, particularly in large and medium-sized NPs. To what extent and how this overexpression pattern is related to the previously shown elevated pain threshold under normal and lesion conditions is discussed [Grass, S., Crawley, J.N., Xu, X.J., Wiesenfeld-Hallin, Z., 2003a. Reduced spinal cord sensitization to C-fibre stimulation in mice over-expressing galanin. Eur. J. Neurosci. 17, 1829-1832; Hygge-Blakeman, K., Brumovsky, P., Hao, J.X., Xu, X.J., Hökfelt, T., Crawley, J.N., Wiesenfeld-Hallin, Z., 2004. Galanin over-expression decreases the development of neuropathic pain-like behaviour in mice after partial sciatic nerve injury. Brain Res. 1025, 152-158].

Crosstalk between Jagged1 and GDNF/Ret/GFRalpha1 signalling regulates ureteric budding and branching

Glial-Cell-Line-Derived Neurotrophic Factor (GDNF) is the major mesenchyme-derived regulator of ureteric budding and branching during nephrogenesis. The ligand activates on the ureteric bud epithelium a receptor complex composed of Ret and GFRalpha1. The upstream regulators of the GDNF receptors are poorly known. A Notch ligand, Jagged1 (Jag1), co-localises with GDNF and its receptors during early kidney morphogenesis. In this study we utilized both in vitro and in vivo models to study the possible regulatory relationship of Ret and Notch pathways. Urogenital blocks were exposed to exogenous GDNF, which promotes supernumerary ureteric budding from the Wolffian duct. GDNF-induced ectopic buds expressed Jag1, which suggests that GDNF can, directly or indirectly, up-regulate Jag1 through Ret/GFRalpha1 signalling. We then studied the role of Jag1 in nephrogenesis by transgenic mice constitutively expressing human Jag1 in Wolffian duct and its derivatives under HoxB7 promoter. Jag1 transgenic mice showed a spectrum of renal defects ranging from aplasia to hypoplasia. Ret and GFRalpha1 are normally downregulated in the Wolffian duct, but they were persistently expressed in the entire transgenic duct. Simultaneously, GDNF expression remained unexpectedly low in the metanephric mesenchyme. In vitro, exogenous GDNF restored the budding and branching defects in transgenic urogenital blocks. Renal differentiation apparently failed because of perturbed stimulation of primary ureteric budding and subsequent branching. Thus, the data provide evidence for a novel crosstalk between Notch and Ret/GFRalpha1 signalling during early nephrogenesis.

Loss of forebrain cholinergic neurons and impairment in spatial learning and memory in LHX7-deficient mice

The identification of the genetic determinants specifying neuronal networks in the mammalian brain is crucial for the understanding of the molecular and cellular mechanisms that ultimately control cognitive functions. Here we have generated a targeted allele of the LIM-homeodomain-encoding gene Lhx7 by replacing exons 3-5 with a LacZ reporter. In heterozygous animals, which are healthy, fertile and have no apparent cellular deficit in the forebrain, b-galactosidase activity reproduces the pattern of expression of the wild-type Lhx7 locus. However, homozygous mutant mice show severe deficits in forebrain cholinergic neurons (FCNs), while other classes of forebrain neurons appear unaffected. Using the LacZ reporter as a marker, we show that in LHX7-deficient mice FCN progenitors survive but fail to generate cholinergic interneurons in the striatum and cholinergic projection neurons in the basal forebrain. Analysis of behaviour in a series of spatial and non-spatial learning and memory tasks revealed that FCN ablation in Lhx7 mutants is associated with severe deficits in spatial but only mild impairment of non-spatial learning and memory. In addition, we found no deficit in long-term potentiation in mutant animals, suggesting that FCNs modulate hippocampal function independently of its capacity to store information. Overall our experiments demonstrate that Lhx7 expression is required for the specification or differentiation of cholinergic forebrain neurons involved in the processing of spatial information.

Hereditary hormone excess: genes, molecular pathways, and syndromes

Hereditary origin of a tumor helps toward early discovery of its mutated gene; for example, it supports the compilation of a DNA panel from index cases to identify that gene by finding mutations in it. The gene for a hereditary tumor may contribute also to common tumors. For some syndromes, such as hereditary paraganglioma, several genes can cause a similar syndrome. For other syndromes, such as multiple endocrine neoplasia 2, one gene supports variants of a syndrome. Onset usually begins earlier and in more locations with hereditary than sporadic tumors. Mono- or oligoclonal ("clonal") tumor usually implies a postnatal delay, albeit less delay than for sporadic tumor, to onset and potential for cancer. Hormone excess from a polyclonal tissue shows onset at birth and no benefit from subtotal ablation of the secreting organ. Genes can cause neoplasms through stepwise loss of function, gain of function, or combinations of these. Polyclonal hormonal excess reflects abnormal gene dosage or effect, such as activation or haploinsufficiency. Polyclonal hyperplasia can cause the main endpoint of clinical expression in some syndromes or can be a precursor to clonal progression in others. Gene discovery is usually the first step toward clarifying the molecule and pathway mutated in a syndrome. Most mutated pathways in hormone excess states are only partly understood. The bases for tissue specificity of hormone excess syndromes are usually uncertain. In a few syndromes, tissue selectivity arises from mutation in the open reading frame of a regulatory gene (CASR, TSHR) with selective expression driven by its promoter. Polyclonal excess of a hormone is usually from a defect in the sensor system for an extracellular ligand (e.g., calcium, glucose, TSH). The final connections of any of these polyclonal or clonal pathways to hormone secretion have not been identified. In many cases, monoclonal proliferation causes hormone excess, probably as a secondary consequence of accumulation of cells with coincidental hormone-secretory ability.

Use of genetically engineered transgenic mice to investigate the role of galanin in the peripheral nervous system after injury

The neuropeptide galanin is present at high levels within the dorsal root ganglia (DRG) and spinal cord during development and after peripheral nerve damage in the adult. This pattern of expression suggests that it may play a role in the adaptive response of the peripheral nervous system (PNS) to injury. Several experimental paradigms have demonstrated that galanin modulates pain transmission, particularly after nerve injury. In our laboratory we have used a transgenic approach to further elucidate the functions of galanin within the somatosensory system. We have generated mice which over-express galanin (either inducibly after nerve injury, or constitutively), and knock-out (KO) mice, in which galanin is absent in all cells, throughout development and in the adult. Analysis of the nociceptive behaviour of the galanin over-expressing animals, before and after nerve injury, supports the view that galanin is an inhibitory neuromodulator of spinal cord transmission. In apparent contradiction to these findings, galanin KO animals fail to develop allodynia and hyperalgesia after nerve injury. However, further studies have shown that galanin is critical for the developmental survival of a subset of small diameter, unmyelinated sensory neurons that are likely to be nociceptors. This finding may well explain the lack of neuropathic pain-like behaviour after injury in the KO animals. Furthermore, the developmental survival role played by galanin is recapitulated in the adult where the peptide is required for optimal neuronal regeneration after injury, and in the hippocampus where it plays a neuroprotective role after excitotoxic injury.

Transgenic overexpression of galanin in the dorsal root ganglia modulates pain-related behavior

The neuropeptide galanin is expressed in the dorsal root ganglia (DRG) and spinal cord and is thought to be involved in the modulation of pain processing. However, its mechanisms of action are complex and poorly understood, as both facilitatory and inhibitory effects have been described. To understand further the role played by galanin in nociception, we have generated two transgenic lines that overexpress galanin in specific populations of primary afferent DRG neurons in either an inducible or constitutive manner. In the first line, a previously defined enhancer region from the galanin locus was used to target galanin to the DRG (Gal-OE). Transgene expression recapitulates the spatial endogenous galanin distribution pattern in DRG neurons and markedly overexpresses the peptide in the DRG after nerve injury but not in the uninjured state. In the second line, an enhancer region of the c-Ret gene was used to constitutively and ectopically target galanin overexpression to the DRG (Ret-OE). The expression of this second transgene does not alter significantly after nerve injury. Here, we report that intact Ret-OE, but not Gal-OE, animals have significantly elevated mechanical and thermal thresholds. After nerve damage, using a spared nerve-injury model, mechanical allodynia is attenuated markedly in both the Gal-OE and Ret-OE mice compared with WT controls. These results support an inhibitory role for galanin in the modulation of nociception both in intact animals and in neuropathic pain states.