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  • Original Articles
  • Open Access

Expression of Human GLI in Mice Results in Failure to Thrive, Early Death, and Patchy Hirschsprung-like Gastrointestinal Dilatation

  • 1,
  • 1,
  • 1,
  • 1,
  • 1 and
  • 1Email author
Molecular Medicine19973:BF03401719

https://doi.org/10.1007/BF03401719

  • Accepted: 20 October 1997
  • Published:

Abstract

Background

GLI is an oncodevelopmental gene in the vertebrate hedgehog/patched signaling pathway that is spatiotemporally regulated during development and is amplified in a subset of human cancers. GLI is the prototype for the Gli-Kruppel family of transcription factors, which includes the Drosophila segment polarity gene ci, the C. elegans sex-deteimining gene tra-1, and human and mouse GLI3, all of which contain a conserved domain of five C2-H2 zinc fingers. GLI3 mutations have been implicated in the mouse mutant extra toes, as well as in human Greig cephalopolydactaly syndrome and the autosomal dominant form of Pallister-Hall syndrome. As such, GLI and the vertebrate hedgehog/patched signaling pathway appear to play important roles in both normal development and neoplasia.

Materials and Methods

Since it is not known whether aberrant GLI expression is similarly linked to developmental disorders, we developed gain-of-function transgenic mice which express human GLI ectopically.

Results

Affected transgenic mice exhibit a phenotype of failure to thrive, early death, and Hirschsprung-like patches of gastrointestinal dilatation. The colons of affected mice have greatly attenuated smooth muscle layers and abnormal overlying epithelium. The density of myenteric plexuses is reduced in the colonic walls. The severity of the phenotype is related to the level of transgene expression.

Conclusions

The transgenic mouse model supports a role for GLI in gastrointestinal development. As part of the vertebrate hedgehog/patched signaling pathway, GLI is essential to mesoderm and CNS ectoderm development and transgenic GLI expression affects neuronal, muscular, and epithelial cell differentiation in the gut. Expression of human GLI in mice results in impairment of enteric neuronal development and a Hirschsprung-like phenotype.

Introduction

GLI is the prototypical gene of the Gli-Kruppel family of transcription factors and is a mediator of hedgehog/patched signaling (14). The pathway is highly conserved, with homologous genes present in C. elegans, Drosophila, chick, mouse, and human (57). The vertebrate hedgehog/patched signaling pathway has been shown to be essential for normal development (8,9). Mutations of the genes Sonic Hedgehog, Patched, and GLI3 cause the human disorders holoprosencephaly (10), basal cell nevus syndrome (1), and Greig cephalopolydactyly syndrome (12) and Pallister-Hall syndrome (1315), respectively. In vertebrates there are three GLI genes based on sequence homology in the region coding for the zinc finger DNA binding domains; GLI, GLI2, and GLI3. The human GLI gene has not yet been linked to a known developmental disorder, but its amplification in some gliomas, osetosarcomas, and rhabdomyosarcomas suggests an important role in growth regulation (16).

The human GLI gene is expressed in the human embryonal carcinoma cell lines Tera-1 and NTera-2 but not in normal adult tissues, except for very low levels in testes, myometrium, cerebellum, and oviduct (3,17). To localize the expression of mouse gli during development, in situ hybridization studies were performed on wild-type mouse embryos. In E7.5 mouse embryos, gli transcripts were present in ectoderm and mesoderm, but not in endoderm. In E10 through E18 embryos, gli transcripts were present in the primordia of the central nervous system, skeletal system, and the gastrointestinal (GI) tract. Expression was evident in the mesoderm of developing GI tract, Meckel’s precartilage mesenchyme, the basis occipitus, rib mesenchymal condensations, primordial vertebral bodies, digital mesenchymal condensations in forefoot and hindfoot plates, the ependymal layer of the spinal cord, most anterior and ventral parts of the telencephalon, several regions of the ventral mesencephalon, and the developing choroid plexus (8,9).

Here we report the production of transgenic mice which express human GLI. The transgenic animals display a complex phenotype related to the level of transgene expression, which includes abnormal development of the colon and patchy Hirschsprung-like dilatation. The colonic defect is associated with abnormal epithelium and decreased density of myenteric plexuses.

Materials and Methods

Transgenic Mice

To generate gain-of-function mice, full-length human GLI cDNA was ligated to the inducible 770 bp mouse metallothionein-1 (pMT-1) promoter. An SV40 small t intron was inserted between pMT-1 and GLI, and the plasmid was cut with BssHII to yield a 4.7 kb fusion gene for microinjection. We then microinjected 2 µg/µl DNA into the pronucleus of one-cell ICR mouse embryos, which were transferred to pseudopregnant CB6F1 surrogate mothers. Southern blot analysis of mouse tail DNA identified one male founder, which was bred to a wild-type ICR female. The GLI transgene showed Mendelian transmission, and hemizygous Fl siblings (GLI/+) were mated to produce homozygous transgenic mice (GLI/GLI), which were identified by Southern blot analysis. Homozygosity was confirmed by analysis of the test-cross offspring.

DNA Isolation

One-half centimeter of mouse tail was incubated in 1 ml lysis buffer (50 mM Tris, pH 9.0, 50 mM EDTA, 0.4 M NaCl, 5 mM DTT, 2.5 mM Spermidine, 1% SDS, 1 mg/ml fresh Proteinase K) at 55°C overnight. The supernatant was mixed with 5 ml lysis buffer B (50 mM Tris, pH 8.0, 50 mM EDTA, 400 mM NaCl) and 2 ml saturated NaCl. After centrifuging, 5 ml isopropanol was added to the supernatant and mixed by swirling. The DNA was redissolved in TE.

RNA Isolation

Total RNA or poly (A)+ RNA were isolated with Qiagen RNeasy™ or Oligotex™ mRNA kits, respectively. For reverse transcription-polymerase chain reaction (RT-PCR), total RNA was treated with RNase-free DNase, which was removed from the RNA samples with RNeasy™ columns.

Southern Hybridization Analysis

Five micrograms of genomic DNA from each mouse was digested with BamHI and XbaI and electrophoresed on 0.8% agarose gels, then transferred to Bio-Rad Zeta-probe membranes in 0.4 M NaOH for 2–3 hr. The membranes were air-dried and baked at 80°C for 30 min. The probe for Southern analysis was a 2.1 kb fragment of human GLI cDNA cut with XhoII and was labeled with a random primer labeling kit at 109 cpm/µg specific activity. The membranes were prewet with hybridization solution (0.5 M NaH2PO4, pH 7.2 and 7% SDS) and hybridized at 65°C overnight in 3 ml of hybridization solution; the final probe concentration was 2 × 106 cpm/ml. After hybridization, the membranes were washed three times at 65°C in 20 mM Na2HPO4, pH 7.2, 1% SDS solution.

RT-PCR

One hundred nanograms of total RNA or 50 ng of poly (A)+ RNA was treated with RNase-free DNase I (Boehringer Mannheim), and RT-PCR was performed using the GeneAmp RNA PCR kit (Perkin Elmer Cetus). The reverse transcription reaction was performed at room temperature for 10 min for annealing and at 42°C for 50 min for synthesis of cDNA, then at 99°C for 5 min, and finally placed on ice until the reaction buffer for PCR amplification was added. Primers and polymerase were added for PCR amplification. The method distinguished between endogenous and transgene expression by using human-specific primers (5′-GACCATGCACTGTCTTGACA-3′ and 5′-AGTCATACTCACGCCTCGAA-3′) to amplify a 238 bp fragment of the transgene.

Quantitative PCR

RT-PCR reactions were carried out using five concentrations of RNA. Band intensities were quantified using NIH Image after digital scanning. Linear response ranges were established for both actin and the transgene RT-PCR product. Actin-to-transgene band intensity ratios were established and compared using data points from the 10-ng reactions, which were within the linear ranges of both actin and the transgene.

Results

Generation of GLI Gain-of-Function Transgenic Mice

To study GLI expression in vivo, we generated gain-of-function transgenic mice expressing full-length human GLI cDNA under the control of the inducible mouse metallothionein-1 (pMT-1) promoter; microinjections were performed using standard techniques (18). Homozygosity was confirmed by Southern blot analysis of mouse tail DNA and test cross (Fig. 1). The mice were divided into four groups: wild type, wild type with zinc supplementation (25 mM ZnSO4 in drinking water), transgenic mice, and transgenic mice with zinc supplementation. Zinc treatment to induce transgene expression in treated groups was first administered to pregnant mothers and then to pups throughout life. Zinc treatment had no effect on wild-type mice.
Fig. 1
Fig. 1

GLI transgenic mice

The transgene construct comprised full-length human GLI under the control of the 770 bp mouse metallothionein (pMT-1) promoter, separated by the SV40 small t intron. The 4.7 kb fusion gene was released from the plasmid by BssHII digestion and was microinjected into the pronuclei of fertilized mouse eggs. (A) Pedigree of the GLI transgenic mice. The four-digit designation for each mouse denotes the generation, litter number, and specific animal. (B, left) F1 litter Southern hybridization analysis: for each animal, 5 µg mouse tail genomic DNA was digested with BamHI and XbaI, then hybridized under stringent conditions with a 2.1 kb XhoII-digested human GLI cDNA probe. Lanes 1, 3, 4, 5, 7, and 8 are transgenic animals; lanes 2, 6, and 9 are nontransgenic litter mates. The arrow indicates the predicted 2.9 kb band. (B, right) Southern blot analysis of homozygous transgenic mice resulting from hemizygous Fl mating. Lane 1 is an F1 hemizygous transgenic animal; lanes 2–5 were presumed to be homozygous transgenic animals because of their double-intensity hybridization signals. This was subsequently proved by breeding.

GLI Transgenic Mice Exhibit Failure to Thrive, Premature Death, and Hirschsprung-like Gastrointestinal Dilatation

Fifty-one percent of the Zn++-induced GLI homozygotes failed to grow normally; on average, they were 40% smaller than comparably aged control animals (Fig. 2A). It is not known why only some of the induced transgenic animals demonstrated this phenotype. The small mice did continue to grow, and their growth curves remained parallel to those of unaffected mice (Fig. 2B). A few small animals were also noted in the noninduced homozygous group, suggesting leaky induction of GLI transgene expression. Interestingly, the females were twice as likely to demonstrate the undersized phenotype (Fig. 2C). Several of the small males were noted to have priapism. In addition to inhibited growth, many of the homozygous mice died prematurely. Of the zinc treated transgenic animals, 35.2% died between 1 and 4 days after birth; additional zinc-treated mice died at 3 to 4 weeks of age, and a significant number of transgenic animals with or without zinc treatment died between 3 and 6 months of age. Within 6 months, 60.3% of the zinc-induced animals and 25.5% of the nonzinc-induced homozygotes died. In contrast, none of the wild-type mice died during this period (Fig. 2D).
Fig. 2
Fig. 2

Failure to thrive and premature death in homozygous GLI transgenic mice

(A) Four-week old mice, from right to left: normal wild-type CD-1 mouse, homozygous noninduced transgenic mouse, three Zn++-induced homozygous transgenic mice. (B) Growth curves of male (top) and female (bottom) mice illustrate failure to thrive in a subset of Zn++-induced homozygous transgenic animals. Growth of small animals remains parallel to the growth of unaffected animals. Points represent mean values. : wild-type Zn++-noninduced, n = 17 females, 24 males; : wild-type Zn++-induced, n = 12 females, 9 males; : heterozygous Zn++-noninduced, n = 16 females, 6 males; : heterozygous Zn++-induced, n = 11 females, 11 males; □: homozygous Zn++-noninduced, n = 7 females, 7 males; ■: homozygous small-sized animals Zn++-induced, n = 14 females, 5 males; : homozygous normal sized animals Zn++-induced, n = 9 females, 13 males. There is no significant difference between wild type Zn++-induced and the other groups except homozygous GLI transgenic small-sized animals Zn++-induced. P < .05 for both male and female (t-test). (C) Failure to thrive was defined as weight smaller than 2 SD below wild-type weight. The phenotype was more prevalent in females than in males. P < .03 (Fisher’s. exact test). (D) Cumulative premature death in homozygous GLI transgenic mice. Zn++ (+): homozygous transgenic mice fed 25 mM ZnSO4 in drinking water since conception; Zn++ (−): homozygous transgenic mice without supplemental zinc; control group: wild-type animals with Zn++-induction. The y-axis is cumulative mortality in percentage.

GLI is normally expressed during the development of gastrointestinal mesoderm, so it was hypothesized that normal GI tract development might be affected in GLI transgenic mice. The transgenic mice showed histologic and gross intestinal abnormalities. Seven of 13 dissected homozygous mice displayed a Hirschsprung-like phenotype of patchy dilatation of the intestinal wall from the ileum to the colon (Fig. 3A, E, F). Hematoxylin and eosin-stained tissue showed that the smooth muscle layer of the gastrointestinal wall was attenuated and the number of myenteric plexuses was greatly reduced in affected regions (Table 1); neuron-specific enolase (NSE) stains confirmed that plexuses were virtually absent from the affected areas (Fig. 3B). Some NSE-positive material suggested the presence of preganglionic fibers in affected areas of colonic wall. In unaffected regions of the same specimens, myenteric plexuses were present, but at a reduced number compared with control colon. In regions of attenuated smooth muscle the overlying colonic epithelium was distinctly abnormal, with greatly decreased overall thickness and relative absence of goblet cells. The attenuated epithelium was low cuboidal and arrayed in small pseudovilli (Fig. 3A, B). Complete epithelial development has been shown to require correct signaling from underlying mesodermal elements (1922). It is possible that dysregulated GLI expression in the mesoderm of the developing GI tract results directly both in improper smooth muscle development and functionally abnormal GI epithelium. Our results indicate, on the other hand, that transgene expression resulted in abnormal enteric nerve development, which in turn caused abnormal development of colonic smooth muscle.
Fig. 3
Fig. 3

Gastrointestinal phenotype in GLI transgenic mice

(A) Attenuation of smooth muscle (sm) in colon of homozygous transgenic mouse 2402. (B) Neuron-specific enolase (NSE) shows normal myenteric plexuses (brown-stained structures, m) in the unaffected musculature. (C, D) Normal mouse colon. Note scale bar; the magnification in D is one-half that of A and C. Scale bars in A–D are 75 µm. (E) Segmental dilatation in homozygous transgenic mouse 3502 with Zn++ induction. Arrows indicate dilatation and attenuation of intestine wall in the colon. c-caecum (F) Low-magnification view of a transverse section of colon from animal 5305 showing relatively unaffected muscle and epithelium (arrow), severely affected muscle with abnormal epithelium (triple arrow), and transitional zones (double arrow). Bar = 2 mm.

Table 1

Number of myenteric plexuses/mm in transverse sections of colon

 

Wild-type CD-1

Healthy Tg with Zn

Sick Tg with Zn

Sick Tg; normal wall

Sick Tg; transitional wall

Sick Tg; thin wall

n a

22, 2

30, 2

116, 3

6, 1

13, 1

16, 1

Number of myenteric plexuses

5.1 ± 1.1

1.9 ± 1.3

1.2 ± 1.4

4.3 ± 1.2

3.1 ± 1.0

0.3 ± 0.6

  

*

*

N.S.

*

*

aDensity of myenteric plexuses in colon wall was determined by examining H&E sections taken randomly for wild type, healthy transgenic (Tg), and sick Tg, and selected as described for normal wall, transitional wall, and thin wall. Wild-type CD-1 mice were nontransgenic. Healthy Tg with Zn were Tg mice with induction of transgene expression but which did not show illness (small size, poor grooming, poor mobility) at the time of sacrifice. These animals, however, did display thinning of the colonic wall with a patchy distribution. Sick Tg with Zn were Tg mice with induction of transgene expression which did show illness (small size, poor grooming, poor mobility). n, number of sections examined, number of animals examined; Tg, transgenic.

*p < 0.0001; N.S. = not significant (Mann-Whitney Test).

Other tissues known to express GLI in normal development were not shown to be affected in the transgenic mice. A complete histologic evaluation of the central nervous system of a 3-month-old transgenic animal showed no abnormalities, and X-ray examination showed no changes in the skeleton. Blood panels and chemistries were all within normal limits, with no evidence of renal or hepatic failure that might have accounted for the failure-to-thrive phenotype. On necropsy, there was no evidence of bowel perforation, peritonitis, or gross mechanical obstruction.

Phenotype Severity Correlates with Increased GLI Transgene Expression

RT-PCR was used to demonstrate expression of the transgene using primers specific for human GLI; mouse gli was not amplified in this system (Fig. 4A, B). The RT-PCR reaction was sensitive to RNase and resistant to DNase I, which indicates that the product was amplified from mRNA rather than contaminating genomic DNA. Transgenic mRNA was detected in neonatal abdomen and chest tissue as well as in adult mouse brain, liver, intestine, and lung (Fig. 4B). GLI transgene expression was not detected in skeletal muscle.
Fig. 4
Fig. 4

Transgene expression detected by RT-PCR

DNase I-treated RNA was used for all reactions, and the predicted 238 bp band is shown. (A) Low concentrations of RNase reduced the amplified transgene produced by RT-PCR. Absence of reverse transcriptase results in no amplification, indicating that DNase I treatment eliminated all of the DNA and that the amplified product results from RNA-derived cDNA generated by the reverse transcriptase. Samples came from intestine of homozygous transgenic animals 4402 (lanes 1–3), 4302 (lanes 4, 5), and 4503 (lanes 6, 7). Lanes 1, 4, and 6: reaction with reverse transcription; lane 2: reaction with reverse transcription plus pretreatment with low concentration of RNase; lanes 3, 5, and 7: reaction without reverse transcription. (B) Multiple-tissue expression of transgene. Lanes 1–4: brain, intestine, liver, lung RNA from animal 4402; lane 5: liver from animal 4302; lane 6: liver RNA from animal 4503; lane 7: intestinal RNA from animal 4503; lane 8: abdominal and chest RNA in day 1 newborn animal 4301; lane 9: abdominal and chest RNA in day 2 newborn animal 4501. (C) Quantitative RT-PCR from intestinal RNA from animals 5308 and 4603. Lanes 1–5: actin and gli expression in a sick, zinc-induced transgenic animal (5308); lanes 6–10: actin and gli expression in a healthy, Zn++-induced transgenic animal (4603). Lanes 1 and 6: 5 ng RNA; lanes 2 and 7: 10 ng RNA; lanes 3 and 8: 20 ng RNA; lanes 4 and 9: 40 ng RNA; lanes 5 and 10: 80 ng of RNA. Actin expression was linear from 5 to 20 ng, and GLI expression was linear from 5 to 40 ng of intestinal RNA. (D) Quantification of relative RNA expression. The ratio of GLI/actin band intensities from gels as those shown in C were compared using NIH Image after digital scanning.

Quantitative RT-PCR studies showed that zinc induction was clearly linked to transgene expression and that the severity of the phenotype was related to the level of transgene GLI expression (Fig. 4C, D). Homozygous zinc-induced transgenic mice demonstrating the “sick” phenotype (small size, poor grooming, poor mobility) showed a 3.1-fold increase in intestinal transgene GLI RNA levels compared with healthy, noninduced mice. Healthy transgenic animals induced with zinc expressed 2.5 times the amount of intestinal transgene RNA compared with their noninduced healthy transgenic counterparts. Liver tissue from noninduced animals also showed that the quantity of transgene RNA correlated with phenotype; sick animals demonstrated 5.1 times the transgene RNA of healthy ones. In adult mice, endogenous mouse gli expression is limited to the brain, testes, and uterus. These results show that message levels have an effect on the phenotype of the transgenic animals.

Discussion

These results demonstrate that expression of human GLI cDNA in mice can lead to a distinctive phenotype involving failure to thrive, premature death, and patchy Hirschsprung-like gastrointestinal dilatation. In this model, dysregulation of GLI has a profound effect. There is dysmorphogenesis of the colon of the animals with decreased density of myenteric plexuses in the colonic wall. The gain-of-function phenotype is transgene dose-dependent, as demonstrated by RT-PCR of transgene expression levels. The phenotype of the zinc-induced homozygous mice is more extreme than that of the noninduced animals.

Sonic hedgehog (Shh), one of the vertebrate homologs of Drosophila hedgehog (hh), is the ligand for the patched (ptc) receptor. In flies, hh regulates a negative feedback loop of ptc with ci in which ci activates the expression of dpp and ptc (23). GLI is the vertebrate homolog of ci, and Bmp-2/4 are the vertebrate homologs of dpp. Dysregulation of dpp in Drosophila disrupts normal midgut constriction (21,24), and dysregulation of Shh causes ectopic expression of Bmp-4 and Hoxd genes in chick hindgut mesoderm (25). Mouse gli is highly expressed in the mesodermal layer of normal GI tract from E13 until birth (8,26). Thus, the essential elements of a mesoderm-epithelial signaling network in the GI tract involving Shh, ptc, gli, and Bmp-4 are conserved from Drosophila to vertebrates. Therefore, ectopic expression of GLI would be expected to disrupt the pathway and result in abnormal gut development; this is precisely the result obtained in the present study. A similar but more posterior phenotype to the one presented here is obtained when Hoxd13 is knocked out in mice (27).

In humans, disruption of Shh results in holoprosencephaly, a very serious dysmorphogenic syndrome with numerous midline defects and axial skeletal abnormalities (10). These patterning defects, including cyclopia, are recapitulated in mice with null mutations of Shh (28). Deletions in the 3′ end of GLI3 in humans results in Pallister-Hall syndrome, manifesting hypothalamic hamartoma, hypopituitarism, polydactyly, imperforate anus, and renal and lung anomalies (13). There is a variant of Pallister Hall syndrome which includes holoprosencephaly and Hirschsprung’s disease (14,15); the genetic defect responsible for this variation is not known, but our results indicate that GLI is a candidate gene.

The role of GLI in GI tract development remains to be established, but since GLI has been placed in the vertebrate hedgehog/patched pathway (11,29), it is reasonable to suppose that GLI is part of a signaling cascade that is important in mesoderm development and in turn affects neuronal, muscular, and epithelial cell differentiation in the gut. In this model, it is likely that impairment of enteric neuronal development led to the Hirschsprung-like phenotype.

Declarations

Acknowledgments

We thank Dr. M. DalCanto for performing the CNS histologic evaluation of the transgenic mice and Dr. P. Chou for histologic evaluation of GI tract walls. This work was aided by grants 93-32 and 94-51 from the American Cancer Society, Illinois Division, Inc. and was supported in part by Public Health Service grant CA64395 from the National Cancer Institute and HD28992 from the National Institute of Child Health and Human Development.

Authors’ Affiliations

(1)
Department of Pediatrics and Children’s Memorial Institute for Education and Research, Northwestern University Medical School, 2300 Children’s Plaza, MC 204, Chicago, Illinois 60614, USA

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Copyright

© Picower Institute Press 1997

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