RNA detection using non-radioactive in situ hybridization

Whole Mount In Situ Hybridization in Murine Tissues

Whole mount in situ hybridization is a sensitive method used to characterize the spatial and temporal expression of RNA transcripts throughout an entire tissue. This method is an excellent tool for studying gene expression during embryonic development. Here, we describe a procedure for digoxigenin labeled in situ hybridization on whole embryos.

Preparation of Adult Mouse Skeletal Tissue Sections for RNA In Situ Hybridization

The RNA in situ hybridization assay is essential in many studies to evaluate gene expression in vivo. It consists of generating tissue sections and subsequently hybridizing these sections with RNA probes. Keeping RNA intact is a challenge while harvesting tissue samples, processing through embedding, sectioning them, and conditioning the sections for hybridization. These challenges are particularly strong for adult skeletal tissues due to their copious, dense, and mineralized extracellular matrices. Here, we describe a method optimized to successfully hybridize RNA species, even of low abundance, in adult mouse bone and cartilage samples. This method involves tissue fixation with paraformaldehyde, demineralization with Morse's solution and paraffin embedding, all of which can be completed in 4 days. Sections are then generated and hybridized using a 1-day standard protocol. Sections prepared using this method are compatible with immunostaining and standard staining procedures for skeletal tissues.

Coordinate expression of pan-neuronal and functional signature genes in sympathetic neurons

Neuron subtypes of the mature nervous system differ in the expression of characteristic marker genes while they share the expression of generic neuronal genes. The regulatory logic that maintains subtype-specific and pan-neuronal genes is not well understood. To begin to address this issue, we analyze RNA sequencing results from whole sympathetic ganglia and single sympathetic neurons in the mouse. We focus on gene products involved in the neuronal cytoskeleton, neurotransmitter synthesis and storage, transmitter release and reception and electrical information processing. We find a particular high correlation in the expression of stathmin 2 and several members of the tubulin beta family, classical pan-neuronal markers. Noradrenergic transmitter-synthesizing enzymes and transporters are also well correlated in their cellular transcript levels. In addition, noradrenergic marker transcript levels correlate well with selected pan-neuronal markers. Such a correlation in transcript levels is also seen between a number of selected ion channel, receptor and synaptic protein genes. These results provide the foundation for the analyses of the coordinated expression of downstream target genes in nerve cells.

F-spondin negatively regulates dental follicle differentiation through the inhibition of TGF-β activity

OBJECTIVE

F-spondin is an extracellular matrix (ECM) protein that belongs to the thrombospondin type I repeat superfamily and is a negative regulator of bone mass. We have previously shown that f-spondin is specifically expressed in the dental follicle (DF), which gives rise to the periodontal ligament (PDL) during the tooth root formation stage. To investigate the molecular mechanism of PDL formation, we investigated the function of f-spondin in DF differentiation.

DESIGN

The expression patterning of f-spondin in the developing tooth germ was compared with that of periodontal ligament-related genes, including runx2, type I collagen and periostin, by in situ hybridization analysis. To investigate the function of f-spondin during periodontal ligament formation, an f-spondin adenovirus was infected into the bell stage of the developing tooth germ, and the effect on dental differentiation was analyzed.

RESULTS

F-spondin was specifically expressed in the DF of the developing tooth germ; by contrast, type I collagen, runx2 and periostin were expressed in the DF and in the alveolar bone. F-spondin-overexpresssing tooth germ exhibited a reduction in gene expression of periostin and type I collagen in the DF. By contrast, the knockdown of f-spondin in primary DF cells increased the expression of these genes. Treatment with recombinant f-spondin protein functionally inhibited periostin expression induced by transforming growth factor-β (TGF-β).

CONCLUSION

Our data indicated that f-spondin inhibits the differentiation of DF cells into periodontal ligament cells by inhibiting TGF-β. These data suggested that f-spondin negatively regulates PDL differentiation which may play an important role in the immature phenotype of DF.

YAP/TAZ Are Mechanoregulators of TGF-β-Smad Signaling and Renal Fibrogenesis

Like many organs, the kidney stiffens after injury, a process that is increasingly recognized as an important driver of fibrogenesis. Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are related mechanosensory proteins that bind to Smad transcription factors, the canonical mediators of profibrotic TGF-β responses. Here, we investigated the role of YAP/TAZ in the matrix stiffness dependence of fibroblast responses to TGF-β In contrast to growth on a stiff surface, fibroblast growth on a soft matrix led to YAP/TAZ sequestration in the cytosol and impaired TGF-β-induced Smad2/3 nuclear accumulation and transcriptional activity. YAP knockdown or treatment with verteporfin, a drug that was recently identified as a potent YAP inhibitor, elicited similar changes. Furthermore, verteporfin reduced YAP/TAZ levels and decreased the total cellular levels of Smad2/3 after TGF-β stimulation. Verteporfin treatment of mice subjected to unilateral ureteral obstruction similarly reduced YAP/TAZ levels and nuclear Smad accumulation in the kidney, and attenuated renal fibrosis. Our data suggest that organ stiffening cooperates with TGF-β to induce fibrosis in a YAP/TAZ- and Smad2/3-dependent manner. Interference with this YAP/TAZ and TGF-β/Smad crosstalk likely underlies the antifibrotic activity of verteporfin. Finally, through repurposing of a clinically used drug, we illustrate the therapeutic potential of a novel mechanointerference strategy that blocks TGF-β signaling and renal fibrogenesis.

Analysis of Mouse Growth Plate Development

To investigate skeletal development, pathophysiological mechanisms of cartilage and bone disease, and eventually assess innovative treatments, the mouse is a very important resource. During embryonic development, mesenchymal condensations are formed, and cells within these mesenchymal condensations either directly differentiate into osteoblasts and give origin to intramembranous bone, or differentiate into chondrocytes and form a cartilaginous anlage. The cartilaginous anlage or fetal growth plate is then replaced with bone. This process is also called endochondral bone development, and it is responsible for the generation of most of our skeleton. Here we discuss in detail the most common in vivo and in vitro techniques our laboratory is currently using for the analysis of the mouse fetal growth plate during development.

Whole-mount in situ hybridization on murine skeletogenic tissues

Whole-mount in situ hybridization (WISH) is a highly sensitive method for spatial and temporal visualization of RNA transcripts throughout an entire tissue. This method is an excellent tool for studying both embryonic development and disease. It is based on sequence complementation between a Digoxigenin (DIG)-labeled antisense RNA probe and the sense RNA transcript of interest in the tissue. The labeled probe is then visualized by immunohistochemical methods using an antibody conjugated to alkaline phosphatase that catalyzes a color reaction.

Radioactive in situ hybridization to detect gene expression in skeletal tissue sections

In situ hybridization (ISH) using RNA probes is a valuable technique to characterize gene expression patterns in animal tissues. It provides valuable spatial information about gene expression. Compared to the nonradioactive alternatives,(35)S radioactive ISH generally provides higher sensitivity. Here, we describe the procedure for(35)S ISH on paraffin sections from the skeletal tissues of mouse embryos.

LIM homeodomain transcription factor Isl1 directs normal pyloric development by targeting Gata3

Background

Abnormalities in pyloric development or in contractile function of the pylorus cause reflux of duodenal contents into the stomach and increase the risk of gastric metaplasia and cancer. Abnormalities of the pyloric region are also linked to congenital defects such as the relatively common neonatal hypertrophic pyloric stenosis, and primary duodenogastric reflux. Therefore, understanding pyloric development is of great clinical relevance. Here, we investigated the role of the LIM homeodomain transcription factor Isl1 in pyloric development.

Results

Examination of Isl1 expression in developing mouse stomach by immunohistochemistry, whole mount in situ hybridization and real-time quantitative PCR demonstrated that Isl1 is highly expressed in developing mouse stomach, principally in the smooth muscle layer of the pylorus. Isl1 expression was also examined by immunofluorescence in human hypertrophic pyloric stenosis where the majority of smooth muscle cells were found to express Isl1. Isl1 function in embryonic stomach development was investigated utilizing a tamoxifen-inducible Isl1 knockout mouse model. Isl1 deficiency led to nearly complete absence of the pyloric outer longitudinal muscle layer at embryonic day 18.5, which is consistent with Gata3 null mouse phenotype. Chromatin immunoprecipitation, luciferase assays, and electrophoretic mobility shift assays revealed that Isl1 ensures normal pyloric development by directly targeting Gata3.

Conclusions

This study demonstrates that the Isl1-Gata3 transcription regulatory axis is essential for normal pyloric development. These findings are highly clinically relevant and may help to better understand pathways leading to pyloric disease.

Yap- and Cdc42-dependent nephrogenesis and morphogenesis during mouse kidney development

Yap is a transcriptional co-activator that regulates cell proliferation and apoptosis downstream of the Hippo kinase pathway. We investigated Yap function during mouse kidney development using a conditional knockout strategy that specifically inactivated Yap within the nephrogenic lineage. We found that Yap is essential for nephron induction and morphogenesis, surprisingly, in a manner independent of regulation of cell proliferation and apoptosis. We used microarray analysis to identify a suite of novel Yap-dependent genes that function during nephron formation and have been implicated in morphogenesis. Previous in vitro studies have indicated that Yap can respond to mechanical stresses in cultured cells downstream of the small GTPases RhoA. We find that tissue-specific inactivation of the Rho GTPase Cdc42 causes a severe defect in nephrogenesis that strikingly phenocopies loss of Yap. Ablation of Cdc42 decreases nuclear localization of Yap, leading to a reduction of Yap-dependent gene expression. We propose that Yap responds to Cdc42-dependent signals in nephron progenitor cells to activate a genetic program required to shape the functioning nephron.

The mammalian kidney undergoes reiterative and stereotypical morphogenetic changes to create the elaborately convoluted adult nephron, the functional filtration unit of the kidney. How these sequential morphological events are controlled remains poorly understood. Here we show that the transcriptional activator Yap is essential in the developing murine kidney. Yap mutants have reduced nephrogenesis and defective morphogenesis. Yap function in nephrogenesis is independent of its previously described role in regulation of cell proliferation and apoptosis. Instead, Yap activity is needed for proper expression of a suite of genes that control cell signaling and cell structure. Remarkably, we find that ablation of Cdc42 phenocopies loss of Yap. We show that Cdc42 is essential for nuclear access of Yap, both in vivo and in tissue culture studies. Taken together, our work shows that Yap and Cdc42 are essential for the cell fate and morphogenesis decisions necessary to shape functioning nephrons, and suggests that Yap functions downstream of Cdc42 during kidney development.

Flexibility of neural stem cells

Embryonic cortical neural stem cells are self-renewing progenitors that can differentiate into neurons and glia. We generated neurospheres from the developing cerebral cortex using a mouse genetic model that allows for lineage selection and found that the self-renewing neural stem cells are restricted to Sox2 expressing cells. Under normal conditions, embryonic cortical neurospheres are heterogeneous with regard to Sox2 expression and contain astrocytes, neural stem cells, and neural progenitor cells sufficiently plastic to give rise to neural crest cells when transplanted into the hindbrain of E1.5 chick and E8 mouse embryos. However, when neurospheres are maintained under lineage selection, such that all cells express Sox2, neural stem cells maintain their Pax6⁺ cortical radial glia identity and exhibit a more restricted fate in vitro and after transplantation. These data demonstrate that Sox2 preserves the cortical identity and regulates the plasticity of self-renewing Pax6⁺ radial glia cells.

Endotoxin and CD14 in the progression of biliary atresia

Background

Biliary atresia (BA) is a typical cholestatic neonatal disease, characterized by obliteration of intra- and/or extra-hepatic bile ducts. However, the mechanisms contributing to the pathogenesis of BA remain uncertain. Because of decreased bile flow, infectious complications and damaging endotoxemia occur frequently in patients with BA. The aim of this study was to investigate endotoxin levels in patients with BA and the relation of these levels with the expression of the endotoxin receptor, CD14.

Methods

The plasma levels of endotoxin and soluble CD14 were measured with a pyrochrome Limulus amebocyte lysate assay and enzyme-linked immunosorbent assay in patients with early-stage BA when they received the Kasai procedure (KP), in patients who were jaundice-free post-KP and followed-up at the outpatient department, in patients with late-stage BA when they received liver transplantation, and in patients with choledochal cysts. The correlation of CD14 expression with endotoxin levels in rats following common bile duct ligation was investigated.

Results

The results demonstrated a significantly higher hepatic CD14 mRNA and soluble CD14 plasma levels in patients with early-stage BA relative to those with late-stage BA. However, plasma endotoxin levels were significantly higher in both the early and late stages of BA relative to controls. In rat model, the results demonstrated that both endotoxin and CD14 levels were significantly increased in liver tissues of rats following bile duct ligation.

Conclusions

The significant increase in plasma endotoxin and soluble CD14 levels during BA implies a possible involvement of endotoxin stimulated CD14 production by hepatocytes in the early stage of BA for removal of endotoxin; whereas, endotoxin signaling likely induced liver injury and impaired soluble CD14 synthesis in the late stages of BA.

Gene transfer by electroporation into hemogenic endothelium in the avian embryo

Hematopoiesis is the dynamic process whereby blood cells are continuously produced in an organism. Blood cell production is sustained by a population of self-renewing multipotent hematopoietic stem cells (HSCs) throughout the life of an organism. Cells with definitive HSC properties appear in the mid-gestation embryo as dense clusters of cells budding from the floor of the aorta, and that of the vitelline and umbilical arteries in the aorta-gonads-mesonephros region. Attempts to genetically modify the aortic floor from which these HSCs arise have been unsuccessful in the mouse, since the regulation of gene expression in the hemogenic endothelium is largely unknown. Here we report the implementation of gene transfer by electroporation into dorsal aortic endothelial cells in the chick embryo. This approach provides a quick and reproducible method of generating gain/loss-of-function models to investigate the function of genes involved in HSC birth.

BMPs and FGFs target Notch signalling via jagged 2 to regulate tooth morphogenesis and cytodifferentiation

The Notch signalling pathway is an evolutionarily conserved intercellular signalling mechanism that is essential for cell fate specification and proper embryonic development. We have analysed the expression, regulation and function of the jagged 2 (Jag2) gene, which encodes a ligand for the Notch family of receptors, in developing mouse teeth. Jag2 is expressed in epithelial cells that give rise to the enamel-producing ameloblasts from the earliest stages of tooth development. Tissue recombination experiments showed that its expression in epithelium is regulated by mesenchyme-derived signals. In dental explants cultured in vitro, the local application of fibroblast growth factors upregulated Jag2 expression, whereas bone morphogenetic proteins provoked the opposite effect. Mice homozygous for a deletion in the Notch-interaction domain of Jag2 presented a variety of severe dental abnormalities. In molars, the crown morphology was misshapen, with additional cusps being formed. This was due to alterations in the enamel knot, an epithelial signalling structure involved in molar crown morphogenesis, in which Bmp4 expression and apoptosis were altered. In incisors, cytodifferentiation and enamel matrix deposition were inhibited. The expression of Tbx1 in ameloblast progenitors, which is a hallmark for ameloblast differentiation and enamel formation, was dramatically reduced in Jag2(-/-) teeth. Together, these results demonstrate that Notch signalling mediated by Jag2 is indispensable for normal tooth development.

Six2 activity is required for the formation of the mammalian pyloric sphincter

The functional activity of Six2, a member of the so/Six family of homeodomain-containing transcription factors, is required during mammalian kidney organogenesis. We have now determined that Six2 activity is also necessary for the formation of the pyloric sphincter, the functional gate at the stomach-duodenum junction that inhibits duodenogastric reflux. Our data reveal that several genes known to be important for pyloric sphincter formation in the chick (e.g., Bmp4, Bmpr1b, Nkx2.5, Sox9, and Gremlin) also appear to be required for the formation of this structure in mammals. Thus, we propose that Six2 activity regulates this gene network during the genesis of the pyloric sphincter in the mouse.

Six2 is required for suppression of nephrogenesis and progenitor renewal in the developing kidney

During kidney development and in response to inductive signals, the metanephric mesenchyme aggregates, becomes polarized, and generates much of the epithelia of the nephron. As such, the metanephric mesenchyme is a renal progenitor cell population that must be replenished as epithelial derivatives are continuously generated. The molecular mechanisms that maintain the undifferentiated state of the metanephric mesenchymal precursor cells have not yet been identified. In this paper, we report that functional inactivation of the homeobox gene Six2 results in premature and ectopic differentiation of mesenchymal cells into epithelia and depletion of the progenitor cell population within the metanephric mesenchyme. Failure to renew the mesenchymal cells results in severe renal hypoplasia. Gain of Six2 function in cortical metanephric mesenchymal cells was sufficient to prevent their epithelial differentiation in an organ culture assay. We propose that in the developing kidney, Six2 activity is required for maintaining the mesenchymal progenitor population in an undifferentiated state by opposing the inductive signals emanating from the ureteric bud.

Establishment of immortalized dental follicle cells for generating periodontal ligament in vivo

The dental follicle is a mesenchymal tissue that surrounds the developing tooth germ. During tooth root formation, periodontal components, viz., cementum, periodontal ligament (PDL), and alveolar bone, are created by dental follicle progenitors. Here, we report the presence of PDL progenitors in mouse dental follicle (MDF) cells. MDF cells were obtained from mouse incisor tooth germs and immortalized by the expression of a mutant human papilloma virus type 16 E6 gene lacking the PDZ-domain-binding motif. MDF cells expressing the mutant E6 gene (MDF( E6-EGFP ) cells) had an extended life span, beyond 150 population doublings (PD). In contrast, normal MDF cells failed to proliferate beyond 10 PD. MDF( E6-EGFP ) cells expressed tendon/ligament phenotype-related genes such as Scleraxis (Scx), growth and differentiation factor-5, EphA4, Six-1, and type I collagen. In addition, the expression of periostin was observed. To elucidate the differentiation capacity of MDF( E6-EGFP ) cells in vivo, the cells were transplanted into severe combined immunodeficiency mice. At 4 weeks, MDF( E6-EGFP ) cell transplants had the capacity to generate a PDL-like tissue that expressed periostin, Scx, and type XII collagen and the fibrillar assembly of type I collagen. Our findings suggest that MDF( E6-EGFP ) cells can act as PDL progenitors, and that these cells may be a useful research tool for studying PDL formation and for developing regeneration therapies.

The Tlx gene regulates the timing of neurogenesis in the cortex

The tailless (tlx) gene is a forebrain-restricted transcription factor. Tlx mutant animals exhibit a reduction in the size of the cerebral hemispheres and associated structures (Monaghan et al., 1997). Superficial cortical layers are specifically reduced, whereas deep layers are relatively unaltered (Land and Monaghan, 2003). To determine whether the adult laminar phenotype has a developmental etiology and whether it is associated with a change in proliferation/differentiation decisions, we examined the cell cycle and neurogenesis in the embryonic cortex. We found that there is a temporal and regional requirement for the Tlx protein in progenitor cells (PCs). Neurons prematurely differentiate at all rostrocaudal levels up to mid-neurogenesis in mutant animals. Heterozygote animals have an intermediate phenotype indicating there is a threshold requirement for Tlx in early cortical neurogenesis. Our studies indicate that PCs in the ventricular zone are sensitive to loss of Tlx in caudal regions only; however, PCs in the subventricular zone are altered at all rostrocaudal levels in tlx-deficient animals. Furthermore, we found that the cell cycle is shorter from embryonic day 9.5 in tlx-/- embryos. At mid-neurogenesis, the PC population becomes depleted, and late PCs have a longer cell cycle in tlx-deficient animals. Consequently, later generated structures, such as upper cortical layers, the dentate gyrus, and the olfactory bulbs, are severely reduced. These studies indicate that tlx is an essential intrinsic regulator in the decision to proliferate or differentiate in the developing forebrain.

Expression and function of periostin-isoforms in bone

Periostin was originally identified in MC3T3-E1 osteoblast-like cells. We have identified an isoform of periostin referred to as periostin-like-factor (PLF). It is homologous to other proteins such as fasciclin I (fas I), MPB70, betaIG-H3, and Algal-CAMs. All of these proteins are implicated in regulating cell adhesion. PLF and the other isoforms of periostin differ in their C-terminal sequences. PLF and periostin differ in two specific regions, between 673 and 699 amino acids (aa) and 785-812 aa. Periostin isoforms are expressed in vivo and in vitro during the stages of osteoblast differentiation and maturation. Their mRNAs are present in pre-osteoblast cells as detected by in situ hybridization, and the proteins are between 86 and 93 kD in size as determined by Western blot analysis. Antisense oligonucleotides and antibodies directed against the isoforms of periostin were used to block the activity of these proteins. In both cases, the levels of osteoblast-specific-differentiation markers were markedly reduced suggesting a role for these proteins in osteoblast differentiation.

A chicken model for DGCR6 as a modifier gene in the DiGeorge critical region

DGCR6 is the most centromeric gene in the human DiGeorge critical region and is the only gene in the region with a second functional copy on a repeat localized more distally on chromosome 22. We isolated the chicken ortholog of DGCR6 and showed an embryonic expression pattern that is initially broad but becomes gradually restricted to neural crest cell derivatives of the cardiovasculature. Retrovirus based gene transduction was used to deliver sense and antisense messages to premigrating neural crest cells in vivo. Embryos in which DGCR6 expression was attenuated revealed cardiovascular anomalies reminiscent of those found in DiGeorge syndrome. Moreover, the expression profiles of three other genes from the DiGeorge critical region, TBX-1, UFD1L, and HIRA, were shown to be altered in this model. TBX-1 and UFD1L levels were increased, whereas HIRA was decreased in the hearts and pharyngeal arches of embryos treated with antisense or partial sense constructs, but not with sense constructs for DGCR6. The expression changes were transient and followed the normal DGCR6 expression profile. These data show that neural crest cells might have a role in the distribution of modulator signals to the heart and pharyngeal arches. Moreover, it shows a repressor function for DGCR6 on the expression of TBX-1 and UFD1L. For the first time, DiGeorge syndrome is shown to be a contiguous gene syndrome in which not only several genes from the critical region, but also different cell types within the embryo, interact in the development of the phenotype.

Signaling dynamics of feather tract formation from the chick somatopleure

In the chick, most feathers are restricted to specific areas of the skin, the feather tracts or pterylae, while other areas, such as the apteria, remain bare. In the embryo, the expansion and closure of the somatopleure leads to the juxtaposition of the ventral pteryla, midventral apterium and amnion. The embryonic proximal somatopleural mesoderm is determined to form a feather-forming dermis at 2 days of incubation (E2), while the embryonic distal and the extra-embryonic somatopleure remain open to determination. We found a progressive, lateral expression of Noggin in the embryonic area, and downregulation of Msx1, a BMP4 target gene, with Msx1 expression being ultimately restricted to the most distal embryonic and extra-embryonic somatopleural mesoderm. Msx1 downregulation thus correlates with the formation of the pterylae, and its maintenance to that of the apterium. Suspecting that the inhibition of BMP4 signaling might be linked to the determination of a feather-forming dermis, we grafted Noggin-expressing cells in the distal somatopleure at E2. This elicited the formation of a supplementary pteryla in the midventral apterium. Endogenous Noggin, which is secreted by the intermediate mesoderm at E2, then by the proximal somatopleure at E4, could be sufficient to suppress BMP4 signaling in the proximal somatopleural mesoderm and then in part of the distal somatopleure, thus in turn allowing the formation of the dense dermis of the future pterylae. The same result was obtained with the graft of Shh-producing cells, but Noggin and Shh are both required in order to change the future amnion into a feather-bearing skin. A possible synergistic role of endogenous Shh from the embryonic endoderm remains to be confirmed.

The TALE homeodomain protein Pbx2 is not essential for development and long-term survival

Pbx2 is one of four mammalian genes that encode closely related TALE homeodomain proteins, which serve as DNA binding partners for a subset of Hox transcription factors. The expression and contributions of Pbx2 to mammalian development remain undefined, in contrast to the essential roles recently established for family members Pbx1 and Pbx3. Here we report that Pbx2 is widely expressed during embryonic development, particularly in neural and epithelial tissues during late gestation. Despite wide Pbx2 expression, mice homozygous mutant for Pbx2 are born at the expected Mendelian frequencies and exhibit no detectable abnormalities in development and organogenesis or reduction of long-term survival. The lack of an apparent phenotype in Pbx2(-)/(-) mice likely reflects functional redundancy, since the Pbx2 protein is present at considerably lower levels than comparable isoforms of Pbx1 and/or Pbx3 in embryonic tissues. In postnatal bone marrow and thymus, however, Pbx2 is the predominant high-molecular-weight (MW)-isoform Pbx protein detectable by immunoblotting. Nevertheless, the absence of Pbx2 has no measurable effect on steady-state hematopoiesis or immune function in adult mice, suggesting possible compensation by low-MW-isoform Pbx proteins present in these tissues. We conclude that the roles of Pbx2 in murine embryonic development, organogenesis, hematopoiesis, immune responses, and long-term survival are not essential.

Analysis of homing receptor expression on infiltrating leukocytes in disease states

Chemokines represent a large family of polypeptides that signal through G-protein-coupled receptors and have a role in chemotaxis, leukocyte homing, inflammation, hematopoiesis, angiogenesis and tumor growth. The chemokine/chemokine receptor system acts in coordination with a complex cytokine network to elicit and direct leukocyte infiltration into the inflamed tissue. In addition to promoting movement into the inflamed tissue, the chemokine/chemokine receptor system may also activate infiltrating cells, such as neutrophils and eosinophils, and induce local damage. In recent years, the elucidation of intricate chemokine networks has led to the identification of potential target molecules for therapeutic intervention. Of considerable interest has been the role of chemokine/chemokine receptors in regulating allergic lung inflammation. In this review, techniques to study in situ expression of chemokine receptors in inflamed tissues are presented and discussed.

The T complex distorter 2 candidate gene, Dnahc8, encodes at least two testis-specific axonemal dynein heavy chains that differ extensively at their amino and carboxyl termini

Homozygosity for the t haplotype allele of the testis-specifically expressed axonemal dynein heavy chain (axDHC) gene, Dnahc8, has been linked to male sterility resulting from aberrant sperm motility. However, the near absence of Dnahc8 expression has been associated with male sterility resulting from an early breakdown in sperm flagellar development. Although axDHCs are integral participants in flagellar motility, a role in flagellar morphogenesis has never been attributed to a member of this highly conserved gene family. To gain a better understanding of this presumed novel role for Dnahc8, we have studied the organization and expression of full-length Dnahc8(+) and Dnahc8(t) transcripts. Our results demonstrate the existence of at least two alternatively spliced, testis-specific Dnahc8 mRNAs transcribed from both the + and t alleles. A highly expressed isoform encodes a protein with significant homology nearly throughout to the gamma heavy chain of the Chlamydomonas axonemal outer arm dynein, while a more poorly expressed isoform codes for a protein whose sequence diverges significantly from that of other axDHCs at both its N and C termini. While in situ hybridization studies demonstrate that both mRNA species accumulate exclusively in mid to late spermatocytes, each isoform shows spatial independence. Additional experiments demonstrate the existence of a testis-expressed mRNA with no significant open reading frame, a portion of which is antisense to the 5'-untranslated region of the highly divergent Dnahc8 isoform. The cumulative data imply that Dnahc8 may have acquired functional plasticity in the testis through the tightly controlled expression of both typical and unusual isoforms.

The dynamic expression pattern of frzb-1 suggests multiple roles in chick development

The Wnt family of secreted proteins has been shown to have multiple roles in embryonic development. Wnt signals are thought to be propagated by binding to the cysteine-rich extracellular domain (CRD) of Frizzled, a seven-transmembrane-domain cell surface receptor. Secreted Frizzled-related proteins (generally denoted Frzb or Sfrp) possess a domain with a high degree of sequence identity and structural similarity with the CRD of Frizzled. Current data indicate that the cysteine-rich domain of secreted Frzb proteins can bind Wnt proteins, suggesting the possibility that Frzbs compete with membrane-bound Frizzled for Wnt binding and consequently act as competitive inhibitors of Wnt signaling. In order to gain a better understanding of the potential roles of Frzb-1 in chick development, we utilized the polymerase chain reaction to isolate a partial cDNA of the chick orthologue of frzb-1, cfrzb-1, and compared its expression pattern to that of Wnt-1, Wnt-3a, Wnt-5a, Wnt-7a, and Wnt-8c. Whole-mount in situ hybridizations have revealed three major phases of expression for cfrzb-1 in the developing chick. The earliest expression of cfrzb-1 is in cells fated to become neural ectoderm in streak-stage embryos. Expression of cfrzb-1 in the neural ectoderm continues up through stage 8. After stage 8, cfrzb-1 expression is gradually attenuated in the closing neural tube of the trunk and is concomitantly up-regulated in neural crest cells. Finally, cfrzb-1 appears in the condensing mesenchyme of the bones in both the limb and the trunk in stage 25+ embryos. Comparative analysis of the cfrzb-1 and the Wnt gene expression patterns suggests possible interactions between cFrzb-1 and all of the Wnt family members examined.

Shared and distinct functions of RAGS and ELF-1 in guiding retinal axons

Two ligands for Eph-related receptor tyrosine kinases, RAGS and ELF-1, have been implicated in the control of development of the retinotectal projection. Both molecules are expressed in overlapping gradients in the tectum, the target area of retinal ganglion cell axons. In two in vitro assays ELF-1 is shown to have a repellent axon guidance function for temporal, but apparently not for nasal axons. RAGS on the other hand is repellent for both types of axons, though to different degrees. Thus, RAGS and ELF-1 share some and differ in other properties. The biological activities of these molecules correlate with the strength of interaction with their receptors expressed on RGC axons. The meaning of these findings for guidance of retinal axons in the tectum is discussed.