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The posterior boundaries of the hnf4a and irx3b domains were similarly shifted anteriorly, and also by unequal extents 3 somites for hnf4a and 1 somite for irx3b ; Fig. The net effect of these changes was a reduction in the rostral domain and expansion in both the central and caudal domains Fig. Despite these patterning changes, the correlations between the rostral-central-caudal domains at 15 somites and the positions of the final nephron segments that we noted in wildtype embryos were likewise the case in lib mutants. For instance, in both wildtypes and lib mutants, the boundaries of the PST segment correlate to the region of overlap between the rostral hnf4a and caudal mecom domains, despite this region being smaller and anteriorly shifted in lib mutants.

These results provide further support for the notion that renal transcription factor domains during early pronephros development are predictive of nephron segment fates at later stages. Between the 20—28 somite stages, lib embryos exhibited similar dynamic spatiotemporal shifts in central and caudal domain markers that we observed in wildtypes Fig. For example, the anterior expression boundary of the central domain gene irx3b and caudal domain marker mecom retracted in lib and wildtypes Fig.

However, there was one exception: Taken together, these results provide genetic evidence that RA has an early role in establishing the rostral and caudal domains within the intermediate mesoderm, and that RA is also required at later time-points to refine the expression patterns of genes such as pou3f3a and pou3f3b. Based on our previous work showing that aldh1a2 was highly expressed in developing somites, we hypothesized that the paraxial mesoderm was a major source of RA responsible for establishing the proximodistal pattern of the pronephros Wingert, et al.

A deficiency in tbx16 was associated with reduced podocytes and proximal tubule segments Fig. For instance, the rostral domain marker hnf4a was reduced, while the central domain marker irx3b and the caudal domain marker mecom were expanded anteriorly Fig. Precise mapping of the segment size differences relative to somite number was not possible in tbx16 morphants due to defective somitogenesis Fig.

Analysis of aldh1a2 expression in tbx16 morphants at the 5 and 28 somite stages showed a significant reduction in transcript levels, consistent with the loss of paraxial mesoderm that characterizes the tbx16 mutant phenotype Amacher, et al. The persistent presence of aldh1a2 transcripts in tbx16 morphants likely represents expression in the lateral plate mesoderm along with a small number of muscle precursors that form in tbx16 mutants Amacher, et al. Whole mount in situ hybridization analysis for nephron segment markers purple and mhc red at the 28 somite stage in wildtype embryos and tbx16 MO-injected embryos.

Embryos are shown in lateral views with anterior to the left. Black brackets and arrows indicate expression domains, and numbers correspond to somite position. A tbx16 knockdown in wildtypes was associated with formation of reduced podocyte numbers, shown by reduced wt1b expression, and shorter proximal segments, shown by smaller nbc1 , slc10a1a and trpm7 gene expression domains; conversely, distal segments were expanded, shown by longer clck , slc12a1 , and slc12a3 expression domains.

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The DL gata3 -expresing segment was unaffected. B tbx16 morpholino injected animals have a reduced rostral domain hnf4a , and shifts in the central irx3b , and caudal mecom domains at 28 somites that are consistent with shorter proximal and expanded distal segments. C—D tbx16 morpholino injected animals have dramatically reduced expression of aldh1a2 at 28 somites C and 5 somites D. Retinoid ligands transduce their effects via heterodimeric complexes of nuclear receptors that consist of a retinoic acid receptor RAR and retinoid X receptor RXR Duester, To explore whether modulations in retinoid receptor activity can alter nephron segmentation, we tested the effects of retinoid receptor antagonists and agonists in wildtype zebrafish embryos.

A striking feature of lib mutants is the significantly enlarged DE segment. Previous studies in Xenopus have demonstrated that Irx3 is needed to specify the distal segments during frog pronephros nephrogenesis Alarcon, et al. While the function of the zebrafish orthologue irx3b has not been assessed, our analysis of early transcription factor expression domains traced irx3b expression in medial nephron progenitors and showed a shift of this expression in lib mutants. To explore the functional importance of irx3b for specifying DE segment fate downstream of RA, we used morpholinos to knockdown this factor and examined nephron segmentation compared to mismatch control-injected animals.

We observed pericardial edema in irx3b morphants at 72 hpf, suggestive of renal failure or salt imbalance data not shown , and analyzed nephron segmentation in irx3b morphants by whole mount in situ hybridization. In place of the DE segment, the proximal segments were slightly expanded, shown by lengthened domains of the PCT marker slc20a1a and PST marker trpm7, such that the boundary between these segments was shifted caudally along the trunk Fig.

In addition, the corpuscle of Stannius CS , a gland derived from the tubular epithelium between the DE and DL segments and marked by gata3 , was dramatically expanded Fig. A Whole mount in situ hybridization analysis for nephron segment markers purple and mhc red at the 28 somite stage in wildtype embryos, irx3b MO-injected embryos, lib homozygous mutants, lib homozygous mutants injected with irx3b MO, DEAB-treated embryos, and DEAB-treated embryos injected with irx3b MO.

DEAB-treated embryos injected with irx3b MO showed expression of irx3b in the same region of the pronephros, suggesting that DE regionalization had been established, but that in the absence of irx3b DE-specific solute transporter expression does not ensue.

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Consistent with the onset of irx3b expression at 15 somites, irx3b- deficient embryos showed no changes in renal gene expression until late somitogenesis. At 28 somites, we found changes in transcription factor domains that correlated with the alterations in the mature nephron segmentation pattern at 28 somites Fig. In addition, the domains of pou3f3a and pou3f3b were shifted posteriorly, such that they were located next to somite 10 compared to somite 9 in wildtype embryos, also corresponding with the shifted position of the PST Fig.

Interestingly, the posterior boundary of pou3f3a was located at somite 14, coincident with the location of the expanded CS population observed in irx3b morphants, and possibly representing ectopic expression in these cells. Lastly, the domains of mecom, emx1, and gata3 were unchanged in irx3b morphants, consistent with the normal location and size of the DL and PD segments Fig. The finding that transcription factor domains were not altered until approximately the 28 somite stage suggests that irx3b function is required late, likely between the 24 and 28 somite stages, to establish a DE-specific gene program and restrict the expression of proximal tubule markers.

These findings indicated that while RA signaling is needed to establish the initial PCT and PST progenitor domains, the ultimate size of these segments is not irrevocably set during early nephron patterning and can be altered by modulating the activity of the later-acting gene irx3b. Recent work in Xenopus has shown that overexpression of Irx3 induces ectopic expression of mature distal tubule markers Alarcon, et al. However, it is not clear whether Irx3 plays an early patterning role during nephron development to specify the DE domain or whether it acts later within this segment to upregulate or restrict gene expression.

This issue is challenging to address in the zebrafish as early markers specific to DE progenitors have not been identified and irx3b transcripts are found in both PST and DE segments. Consistent with this, we found irx3b transcripts in the same region of the nephron as the DE marker slc12a1 at the 28 somite stage Fig. There are many gaps in our knowledge about the mechanisms that accomplish nephron patterning during kidney development. Here, we show that the nephron segments in the zebrafish pronephros arise following an elaborate series of spatiotemporal gene expression changes in the intermediate mesoderm.

We have constructed a detailed transcription factor map that describes this process and is predictive of the mature segmentation pattern of the pronephros. Spatiotemporal expression domains in nephron progenitors during mid- to late-somitogenesis were unaffected by blocking cell proliferation, suggesting that cellular turnover does not significantly account for the dynamic alterations that we detected. Furthermore, our genetic evidence demonstrates that RA is essential for delineating the earliest rostrocaudal patterning events in the intermediate mesoderm, and suggest that RA dosage influences the size and positioning of subsequent transcription factor domains and thereby the mature nephron segmentation pattern.

Together, our study provides a new molecular map that can be utilized to guide future interrogations into the workings of nephrogenesis, and adds additional insights to previous reports about the ways that RA and irx3b influences nephron formation. Several lines of evidence now indicate that retinoid signaling is crucial for pronephros patterning, and that the location of RA, time of production, and dosage are all crucial.

We recently demonstrated that the caudal homeobox genes regulate the locale of RA by establishing the expression domains of the aldh1a2 and cyp26a1 genes Wingert, et al. Axial shifts in the expression of these enzymes were associated with shifts in pronephros position along the embryo trunk, suggesting that the position of RA synthesis had important inductive consequences for nephron patterning Wingert, et al.

It should be noted, however, that the disruption of the formation of the paraxial mesoderm via tbx16 knockdown alters both aldh1a2 expression and leads to other broad defects, thus we cannot eliminate the possibility that the change in nephron patterning in tbx16 morphants is affected by dirsuptions in global patterning.

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Further studies are needed to delineate between RA-specific and other changes. Given the outcomes of genetic or chemical alterations in RA signaling, we favor the hypothesis that RA produced by paraxial mesoderm acts to pattern nephron progenitors. Proximal tubule segment identities rely on RA for their specification, and dramatic alterations in segment fates ensue when RA levels are greatly elevated or repressed: Interestingly, segmentation changes only occur if RA bioavailability was altered from the onset of gastrulation through to early somitogenesis stages, establishing an early role for retinoid signaling in pronephros development.

In this study, our analysis of the lib presumptive null allele and nls hypomorph allele mutants provides genetic evidence that modulating RA levels produces graded effects on the nephron segmentation pattern. By morphological criteria, lib mutants exhibit a more severe RA-deficiency phenotype than nls , and form a slightly shorter PST segment concomitant with an expanded DE segment. The rescue of the lib mutant phenotype accordingly requires treatment with higher levels of exogenous RA than the nls mutant.

Taken together, these lines of evidence suggest that RA dosage determines the size of the proximal tubule domain. This finding could reflect the involvement of other RA receptors during nephron progenitor patterning, though such an interpretation may be complicated by partial drug efficacy in zebrafish cells as compared to other organisms for this particular compound. Future studies, such as RA receptor knockdown experiments, are needed to tease out the specific roles of RA receptors during nephrogenesis, and to address fully whether RA receptor activity is necessary in nephron progenitors themselves.

Our studies raise several intriguing questions about how RA actually affects the nephron progenitors. Cell-autonomy has yet to be assessed regarding RA activity in the nephron progenitors. Another pressing question is whether RA and its receptors cooperate to directly or indirectly modulate the expression of renal genes.

Interestingly, a recent study provided evidence that RA participates actively to trigger gene expression of the kidney podocyte lineage. Abrogation of RA synthesis in the lib mutant this study and with chemical inhibitors to aldh1 enzymes Wingert, et al. These findings illuminate the possibility that RA may act directly, by activating genes required for proximal tubule fate and also by repressing distal caudal domain genes.

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However, these data do not rule out the notion that indirect mechanisms are also operative. Interestingly, changes in RA synthesis are associated with alterations in the earliest regionalization of the intermediate mesoderm. Nephron progenitors display at least two regional identities between the 6—8 somite stages, which we have termed rostral and caudal. We found a fascinating, partial overlap of these domains at the 8 somite stage, perhaps suggestive of a more complex arrangement of molecular identities that will be better understood as more early renal markers are discovered.

Nevertheless, in the lib setting of decreased RA production, the rostral nephron progenitor population is reduced while the caudal population is expanded, and we noted previously that DEAB treatment abrogates the rostral domain entirely Wingert, et al. These data support the notion that RA ultimately works to induce a rostral progenitor identity among nephron progenitors. While the genes involved in nephron patterning downstream of RA are still unclear, the notch ligand genes dlc and jag2 are excellent candidates, given the role of the Notch pathway in promoting proximal tubule fates during mammalian kidney development Cheng, et al.

Irx genes encode homeodomain transcription factors, and members of this gene family have functions in the development of many tissues. In diverse settings ranging from imaginal discs in flies to the vertebrate neural plate, Irx genes act to pattern regional differences amongst cell territories and can both to activate and repress target gene expression Cavodeassi, et al. Irx3 has recently been identified as a requisite player in two aspects of Xenopus pronephros development: In this work, we show a conserved requirement for irx3b in distal tubule differentiation in the zebrafish pronephros.

Consistent with a late role for irx3b during nephron development, alterations in gene expression domains were only detectable in irx3b morphants at time-points that immediately preceded the onset of the segment-specific solute transporter genes. In support of this, there is precedence in other tissues for such diverse targets of Irx factors; regional patterning in the developing vertebrate brain utilizes a system of transcription factor antagonism between Irx3 and Six3, while Irx4 and Irx5 in myocardial cells alters potassium ion channel gene expression Constantini, et al.

We have identified putative Iroquois binding sites upstream of zebrafish slc12a1 , consistent with the possibility that irx3b regulates the expression of this DE-specific transporter Wingert and Davidson, unpublished. In contrast, the role of Irx3 in the maintenance of the pronephros territory does not appear to be conserved in zebrafish, highlighting one functional difference between the frog and zebrafish Irx3 genes.

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In zebrafish, at least four irx orthologues are expressed in the zebrafish pronephros, irx2a, irx3b, irx4a , and irx5a , which may explain the difference between these species Lecaudey, et al. Further, Irx3 expression in Xenopus embryos appears to be positively regulated by retinoids, as fewer transcripts are detected in the absence of retinoids while exogenous RA is associated with elevated transcript numbers Alarcon, et al.

These alterations appear linked to early changes in the mesoderm destined to form the pronephros rather than later proximodistal patterning events Alarcon, et al. While RA similarly appears to function upstream of irx3b in the zebrafish pronephros, changes in the irx3b domain correlate with altered nephron patterning. This study has identified critical roles for RA and irx3b during zebrafish pronephros segmentation, but other vital signals have yet to be determined. Our characterization of transcription factor gene expression in the intermediate mesoderm has revealed a complex molecular profile that is spatially and temporally dynamic, and future functional analysis of these genes will reveal key determinants of segment identity and cross-regulatory interactions.

A similar level of transcriptional complexity is beginning to be realized during mammalian nephrogenesis, largely in part due to the efforts of the GenitoUrinary Development Molecular Anatomy Project GUDMAP , which has mapped the expression of mouse genes to different compartments of the developing metanephric kidney Brunskill, et al, ; Georgas, et al.

Findings from the GUDMAP, as well as previous studies, have documented a set of genes with regionalized domains within murine nephrons. For example, Pou3f3 is restricted to prospective distal regions of the nephron, similar to our observations of the zebrafish orthologues pou3f3a and pou3f3b Nakai, et al. It is likely that many of the same transcriptional pathways underlie proximodistal nephron patterning in all vertebrates.

Therefore our work, establishing a detailed molecular description of gene expression during nephrogenesis, should provide a rich source of data for generating hypothesis-driven experiments in other model organisms such as the mouse. A greater knowledge of the molecular basis of vertebrate nephron development will help elucidate the causes of congenital kidney defects, which are often poorly understood, as well as further our understanding of the regulatory networks that maintain nephron function in the adult.

Zebrafish were maintained and staged as described Kimmel, et al. Families were screened to isolate mutants with kidney development defects, as manifested by edema between 24 and 72 hpf. A panel of CA simple sequence length polymorphisms SSLP markers were used to scan chromosomes and establish linkage as described Wingert, et al.


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For lib rescues and aldh1a2 expression studies, see below , full-length wild-type aldh1a2 was subcloned into the pCS2 expression vector using the EcoRI and XhoI sites. Reported expression patterns show representative results as gathered from analysis of between 10 and 15 animals per each timepoint and genotype mutant studies and knockdown. Gene expression domains as reported by somite boundaries were based on counts of at least 5 separate samples to ensure accurate documentation. For chemical treatments, wild-type embryos were incubated with camptothecin and nocodazole, as described Murphey, et al.

For lib rescue studies, embryos from lib or nls heterozygous incrosses were incubated in RA treatment, as described Wingert, et al. All chemical treatments were fully penetrant and produced consistent results at the doses and treatment windows that were examined. Embryos were injected with pg of cRNA at the 1-cell stage.

For all morpholino experiments, morpholinos were solubulized as recommended by Gene-Tools at and stored at a 4mM concentration. Dilution of morpholino stocks were injected into 1-cell stage wild-type embryos. Whole mount in situ hybridization for cdh17, clck, dlc, gata3, jag2, mecom, mhc, myoD, nbc1, pax2a, pax8, raldh2, wt1a and wt1b were performed as described Wingert, et al. Expression of emx1 , etv5, grhl2a, hnf1ba, hnf1bb, hnf4a, irx3b, pou3f3a, pou3f3b were previously reported Hauptmann and Gerster, ; Kawahara and Dawid, ; Lecaudey, et al.

Nephron progenitors, derived from the intermediate mesoderm IM are situated adjacent to the paraxial mesoderm PM. Subsequent to RA signaling, nephron progenitors are broadly regionalized into rostral and caudal domains by the 6—8 somite stages. At the 15 somite stage, a nested pattern of transcription factor domains suggests the continued presence of broad rostral and caudal domains as well as an overlapping medial domain, defined by irx3b expression. Activity of irx3b sets the DE identity given its dynamic spatiotemporal shifts in this vicinity during later somitogenesis stages.

Segment epithelia have unique solute transporter expression patterns at the 28 somite stage, concomitant with an end to many spatiotemporal transcription factor domain shifts in the nephron progenitors. Whole mount in situ hybridization analysis for nephron segment markers purple and mhc red at the 28 somite stage in wildtype embryos treated with DMSO vehicle alone or camptothecin starting at the 24, 22, 20, 18 and 15 somite stage or B nocodazole starting at the 22 somite stage.

Embryos in all chemical treatments formed PCT, PST, DE, and DL segments at the same somite position as wildtype embryos, consistent with a negligible role for cell proliferation in the establishment of segment domains after the 15 somite stage. The segments detected using the following transcripts for all embryos except the 15 somite stage treatment: The 15 somite stage camptothecin-treated embryos were significantly delayed by the drug treatment and did not show trpm7 or slc12a1 transcripts data not shown.

To probe the existence of these areas, the overlap between hnf4a and irx3b was ascertained, as indicated by a single asterisk for hnf4a and double asterisk for irx3b transcripts. The overlap between hnf4a and irx3b showed the presence of the PCT identity cells that expressed hnf4a only and PST region of cells that expressed both hnf4a and irx3b , a correlation based on that seen in wildtype embryos at this stage. A Lateral views of living 28 somite wildtype and lib embryos compared to embryos injected with aldh1a2 cRNA transcripts. Rescue evaluation was determined by presence of pectoral fins in mutant embryos.

Similar phenotype trends were observed in wildtypes exposed to this dosage of RA. C Summary of nephron segmentation with respect to embryo somite number for each treatment. Gene expression patterns of transcription factors in nephron progenitors in wild-type embryos compared to lib mutant embryos at the 20, 22, 24, and 28 somite stage. Embryos are shown in lateral views with anterior to the left, and have been stained by whole mount in situ hybridization to mark kidney expression purple and the somites with mhc red. Black lines indicate areas of high gene expression, and numbers correspond to the adjacent somite position.

The spatial distributions of hnf1a, hnf4a, and hnf1bb transcripts were unaltered between 20—28 somites 28 somite stage not shown. The distributions of etv5 and irx3b changed in wildtypes and lib at the 28 and 24 somite stages, respectively. The spatial distributions of pou3f3a and pou3f3b transcripts in lib mutants were continually expressed in rostral regions between 20—28 somites 28 somite stage not shown. The distribution of mecom changed progressively in both wildtypes and lib throughout the 20—28 somite stages. The distribution of emx1 and gata3 transcripts was unaltered in wildtypes between the 20—28 somite stages, whereas lib had progressive restrictions of these transcripts to caudal populations.

A Gene expression patterns of transcription factors in nephron progenitors in wildtype embryos and irx3b MO injected animals at the 28 somite stage. In irx3b morphants, the domains of hnf1ba, hnf1g, irx3b, mecom, emx1, and gata3 were unchanged, while the expression of hnf4a was expanded slightly and the rostral boundary of pou3f3a and pou3f3b were shifted distally by one somite. In addition, the pou3f3a domain was expanded to somite B The domain of transcription factor gene expression in wildtype and irx3b morphant embryos correlates closely to the segment pattern.

Foreground Summary of transcription factor expression domains represented by black bars are schematized in the nephrons at the 28 somite stages Note: Background Nephron segment identities form adjacent to particular somites demarcated by numbered columns, top , and each segment region is color-coded to envisage a comparison between the transcription factor expression domains and the nephron segments. RAW wishes to thank the staff of the Center for Zebrafish Research at the University of Notre Dame for providing ongoing husbandry of the lib zebrafish strain.

National Center for Biotechnology Information , U. Author manuscript; available in PMC Jun Wingert 1, 2, 3, 4 and Alan J. Davidson 1, 2, 3, 5. The publisher's final edited version of this article is available free at Dev Dyn. See other articles in PMC that cite the published article. Abstract Kidney nephrons are comprised of proximal and distal tubule segments that perform unique roles in excretion. RESULTS Expression domains are dynamic within the nephron progenitor territory To study the origins of nephron segments, we analyzed the expression of transcription factors and signaling molecules between the time when the intermediate mesoderm is first detected around the 3 somite stage to the emergence of mature nephron segments around 24 hours post fertilization hpf; equivalent to the 28 somite stage Wingert, et al.

Open in a separate window. Pronephros progenitors are delineated into a series of molecularly distinct regions during early somitogenesis that are RA-dependent Gene expression patterns in the nephron territory in wildtype embryos and lib mutants at the A 8 somite stage B 15 somite stage and schematized respectively C—D. Analysis of gene expression domain dynamics in the pronephros progenitors reveals that progressive refinements ultimately correlate with specific segment fates Foreground Gene expression domains represented by black bars are schematized in the pronephros territory between 8 and 28 somite stages.

Dynamic spatiotemporal expression changes during late somitogenesis precede the appearance of segment identities in the pronephros Gene expression patterns of transcription factors in nephron progenitors in wildtype embryos at the 20, 22, 24, and 28 somite stage. Cell proliferation is not essential for nephron segmentation during somitogenesis One possible explanation for the dynamic spatiotemporal alterations in gene expression domains is that regional changes in cell proliferation generate shifts in the physical arrangement of nephron tubule progenitors.

Mutation of the lightbulb gene disrupts proximo-distal patterning of nephron segments We next sought to gain insight into the genetic pathways that establish nephron segment fates. Genetic and chemical models of RA biosynthesis deficiency exhibit a similar nephron segment phenotype of reduced proximal fates and expanded distal fates, and lib is the most severely affected aldh1a2 mutant Whole mount in situ hybridization analysis for nephron segment markers purple and mhc red at the 28 somite stage in aldh1a2 mutants and DEAB-treated wildtype embryos.

Paraxial mesoderm is necessary for proximo-distal nephron patterning Based on our previous work showing that aldh1a2 was highly expressed in developing somites, we hypothesized that the paraxial mesoderm was a major source of RA responsible for establishing the proximodistal pattern of the pronephros Wingert, et al. RA receptor activity is also essential for nephron segment patterning Retinoid ligands transduce their effects via heterodimeric complexes of nuclear receptors that consist of a retinoic acid receptor RAR and retinoid X receptor RXR Duester, RA signals demarcate an early subdivision of pronephros progenitors Several lines of evidence now indicate that retinoid signaling is crucial for pronephros patterning, and that the location of RA, time of production, and dosage are all crucial.

Conserved and unique elements of Irx3 function during zebrafish and frog nephrogenesis Irx genes encode homeodomain transcription factors, and members of this gene family have functions in the development of many tissues. Insights into conserved nephron segmentation mechanisms among vertebrates This study has identified critical roles for RA and irx3b during zebrafish pronephros segmentation, but other vital signals have yet to be determined. Embryo chemical treatments, morpholinos and in situ hybridization analysis Reported expression patterns show representative results as gathered from analysis of between 10 and 15 animals per each timepoint and genotype mutant studies and knockdown.

Model of how RA and irx3b signals sequentially pattern the pronephros territory to generate discrete nephron segments Nephron progenitors, derived from the intermediate mesoderm IM are situated adjacent to the paraxial mesoderm PM. Cell proliferation of pronephros progenitors is not required to establish segment boundaries: Click here to view. Supplemental Figure 2 Supplemental Figure 2. Supplemental Figure 3 Supplemental Figure 3.

Supplemental Figure 4 Supplemental Figure 4. Dynamic alterations in renal transcription factors in lib mutants follow trends similar to wild-type embryos in rostral and central domains: Supplemental Figure 5 Supplemental Figure 5. Dynamic alterations in renal transcription factors in lib mutants show some trends analogous to wild-type embryo caudal domains, but with some differences: Supplemental Figure 6 Supplemental Figure 6.

Transcription factor domain alterations in irx3b morphants correspond to changes in segment boundaries: A dual requirement for Iroquois genes during Xenopus kidney development. Golden knee-high grasses sway in the winds. Bison roam, white-rumped pronghorn antelope dash past in swift-footed herds, and black-tailed prairie dogs poke curious heads out of the ground.

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Visitors have to register with a parks team and take safety training, then a guide leads groups to the park boundary by boat or dog team, skis or snowmobile, depending on the weather. Extreme climbers can brave Mount Thor, a sheer 1,metre face. Guides and outfitters can lead the less experienced. There are no campsites. Backcountry camping is permitted, but watch for polar bears! The hamlet of Pangnirtung is home to the renowned Uqqurmiut arts and crafts centre of Inuit art, with print shop and tapestry studio.

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