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M R Capecchi

Publications and source records attributed to M R Capecchi.

At least 55 records · Page 3Linked to original sources
PubMed1996

Mice with targeted disruption of Hoxb-1 fail to form the motor nucleus of the VIIth nerve.

Mice were generated with targeted disruptions in the hoxb-1 gene. Two separate mutations were created: the first disrupts only the homeodomain and the second inactivates the first exon as well as the homeodomain. The phenotypes associated with these two mutant alleles are indistinguishable in surviving adult mice. The predominant defect in these mutant mice is a failure to form the somatic motor component of the VIIth (facial) nerve, possibly through a failure to specify these neurons. The phenotype of hoxb-1 mutant homozygotes closely resembles features of the clinical profile associated with humans suffering from Bell's Palsy or Moebius Syndrome. These animals should therefore provide a useful animal model for these human diseases.

Animals↗
PubMed1996

Targeted disruption of the Hoxb-2 locus in mice interferes with expression of Hoxb-1 and Hoxb-4.

Mice with a disruption in the hoxb-2 locus were generated by gene targeting. 75% of the hoxb-2 mutant homozygotes died within 24 hours of birth. While a majority of these mice had severe sternal defects that compromised their ability to breathe, some had relatively normal sternum morphology, suggesting that one or more additional factor(s) contributed to neonatal lethality. At 3-3.5 weeks of age, half of the remaining hoxb-2 homozygotes became weak and subsequently died. All of the mutants that survived to 3 weeks of age showed marked facial paralysis similar to, but more severe than, that reported for hoxb-1 mutant homozygotes (Goddard, J. M., Rossel, M., Manley, N. R. and Capecchi, M. R. (1996) Development 122, 3217-3228). As for the hoxb-1 mutations, the facial paralysis observed in mice homozygous for the hoxb-2 mutation results from a failure to form the somatic motor component of the VIIth (facial) nerve which controls the muscles of facial expression. Features of this phenotype closely resemble the clinical signs associated with Bell's Palsy and Moebius Syndrome in humans. The sternal defects seen in hoxb-2 mutant mice are similar to those previously reported for hoxb-4 mutant mice (Ramirez-Solis, R., Zheng, H., Whiting, J., Krumlauf, R. and Bradley. A. (1993) Cell 73, 279-294). The above results suggest that the hoxb-2 mutant phenotype may result in part from effects of the hoxb-2 mutation on the expression of both hoxb-1 and hoxb-4. Consistent with this proposal, we found that the hoxb-2 mutation disrupts the expression of hoxb-1 in cis. In addition, the hoxb-2 mutation changes the expression of hoxb-4 and the hoxb-4 mutation, in turn, alters the pattern of hoxb-2 expression. Hoxb-2 and hoxb-4 appear to function together to mediate proper closure of the ventral thoracic body wall. Failure in this closure results in severe defects of the sternum.

Abnormalities, Multiple↗
PubMed1996

A mutational analysis of the 5' HoxD genes: dissection of genetic interactions during limb development in the mouse.

Using gene targeting in mice, we have undertaken a systematic mutational analysis of the homeobox-containing 5' HoxD genes. In particular, we have characterized the limb defects observed in mice with independent targeted disruptions of hoxd-12 and hoxd-13. Animals defective for hoxd-12 are viable, fertile, and appear outwardly normal yet have minor autopodal defects in the forelimb which include a reduction in the bone length of metacarpals and phalanges, and a malformation of the distal carpal bone d4. The limb phenotypes observed in hoxd-13 mutant mice are more extensive, including strong reductions in length, complete absences, or improper segmentations of many metacarpal and phalangeal bones. Additionally, the d4 carpal bone is not properly formed and often produces an extra rudimentary digit. To examine the genetic interactions between the 5' HoxD genes, we bred these mutant strains with each other and with our previously characterized hoxd-11 mouse to produce a series of trans-heterozygotes. Skeletal analyses of these mice reveal that these genes interact in the formation of the vertebrate limb, since the trans-heterozygotes display phenotypes not present in the individual heterozygotes, including more severe carpal, metacarpal and phalangeal defects. Some of these phenotypes appear to be accounted for by a delay in the ossification events in the autopod, which lead to either the failure of fusion or the elimination of cartilaginous elements. Characteristically, these mutations lead to the overall truncation of digits II and V on the forelimb. Additionally, some trans-animals show the growth of an extra postaxial digit VI, which is composed of a bony element resembling a phalange. The results demonstrate that these genes interact in the formation of the limb. In addition to the previously characterized paralogous interactions, a multitude of interactions between Hox genes is used to finely sculpt the forelimb. The 5' Hox genes could therefore act as a major permissive genetic milieu that has been exploited by evolutionary adaptation to form the tetrapod limbs.

Animals↗
PubMed1996

Mice lacking angiotensin-converting enzyme have low blood pressure, renal pathology, and reduced male fertility.

Mammals produce two isozymes of angiotensin-converting enzyme (ACE). Somatic ACE plays an important role in the control of blood pressure. The function of testis ACE, produced by male and germ cells, is not known. To examine the roles of these isozymes, we used targeted homologous recombination to introduce a modified ACE allele into a mouse line. Mice homozygous for this mutant allele lack both ACE isozymes and have markedly reduced blood pressures. Contrary to a previous report, we found heterozygous male mice to have normal blood pressures. Homozygous mutant mice also have severe renal disease. The renal papilla is markedly reduced, and the intrarenal arteries exhibit vascular hyperplasia associated with a perivascular inflammatory infiltrate. These animals cannot effectively concentrate urine. They also have an abnormally low urinary sodium to potassium ratio despite reduced levels of aldosterone. Homozygous mutant male mice sire significantly smaller litters than wild-type male mice; however, no defect in sperm number, morphology, or motility was detected. ACE-deficient animals demonstrate the role of this enzyme in systemic blood pressure, renal development and function, and male fertility.

Animals↗
PubMed1995

Absence of radius and ulna in mice lacking hoxa-11 and hoxd-11.

Mice with targeted disruptions in Hox genes have been generated to evaluate the role of the Hox complex in determining the mammalian body plan. This complex of 38 genes encodes transcription factors that specify regional information along the embryonic axes. Early in vertebrate evolution an ancestral complex shared with invertebrates was duplicated twice to give rise to the four linkage groups (Hox A, B, C and D). As a consequence, corresponding genes on the separate linkage groups, called paralogues, are most closely related to each other. Based on sequence similarities, the Hox genes have been subdivided into 13 paralogous groups. The five most 5' groups (Hox 9-13) pattern the posterior region of the vertebrate embryo and the appendicular skeleton. Mice with individual mutations in the paralogous genes hoxa-11 and hoxd-11 have been described. By breeding these two strains together we have generated double mutants which have dramatic phenotypes not apparent in mice homozygous for the individual mutations. The radius and the ulna of the forelimb are almost entirely eliminated, the axial skeleton shows homeotic transformations, and there are severe kidney defects not present in either single mutant. The limb and axial phenotypes are quantitative: as more mutant alleles are added to the genotype, the phenotype becomes progressively more severe. The appendicular skeleton defects suggest that paralogous Hox genes function together to specify limb outgrowth and patterning along the proximodistal axis.

Alleles↗
PubMed1995

Genetic interaction between hoxb-5 and hoxb-6 is revealed by nonallelic noncomplementation.

hoxb-5 and hoxb-6 are adjacent genes in the mouse HoxB locus and are members of the homeotic transcription factor complex that governs establishment of the mammalian body plan. To determine the roles of these genes during development, we generated mice with a targeted disruption in each gene. Three phenotypes affecting brachiocervicothoracic structures were found in the mutant mice. First, hoxb-5- homozygotes have a rostral shift of the shoulder girdle, analogous to what is seen in the human Sprengel anomaly. This suggests a role for hoxb-5 in specifying the position of limbs along the anteroposterior axis of the vertebrate body. Second, hoxb-6- homozygotes frequently have a missing first rib and a bifid second rib. The third phenotype, an anteriorizing homeotic transformation of the cervicothoracic vertebrae from C6 through T1, is common to both hoxb-5- and hoxb-6- homozygotes. Quite unexpectedly, hoxb-5, hoxb-6 transheterozygotes (hoxb-5-hoxb-6+/hoxb-5+ hoxb-6-) also show the third phenotype. By this classical genetic complementation test, these two mutations appear as alleles of the same gene. This phenomenon is termed nonallelic noncomplementation and suggests that these two genes function together to specify this region of the mammalian vertebral column.

Alleles↗
PubMed1995

A mouse model for the delta F508 allele of cystic fibrosis.

The most common cause of cystic fibrosis is a mutation that deletes phenylalanine 508 in cystic fibrosis transmembrane conductance regulator (CFTR). The delta F508 protein is misprocessed and degraded rather than traveling to the apical membrane. We used a novel strategy to introduce the delta F508 mutation into the mouse CFTR gene. Affected epithelia from homozygous delta F508 mice lacked CFTR in the apical membrane and were Cl-impermeable. These abnormalities are the same as those observed in patients with delta F508 and suggest that these mice have the same cellular defect. 40% of homozygous delta F508 animals survived into adulthood and displayed several abnormalities found in human disease and in CFTR null mice. These animals should provide an excellent model to investigate pathogenesis and to examine therapies directed at correcting the delta F508 defect.

Alleles↗
PubMed1995

The role of Hoxa-3 in mouse thymus and thyroid development.

Targeted disruption of Hoxa-3 results in a number of regionally restricted defects in tissues and structures derived from or patterned by mesenchymal neural crest. However, analysis of mutant embryos with injections of a carbocyanine dye or with molecular markers that label these cells indicates that neither the amount nor the migration patterns of this neural crest population are grossly affected. Therefore, it appears that the loss of Hoxa-3 affects the intrinsic capacity of this neural crest cell population to differentiate and/or to induce proper differentiation of the surrounding pharyngeal arch and pouch tissues. Hoxa-3 mutant mice are athymic and show thyroid hypoplasia. Thymus development is first evident as an expansion of mesenchymal neural crest in the posterior part of the 3rd pharyngeal pouch. Prior to this expansion, a marked reduction in pax-1 expression is observed in these cells in the mutant embryos. As pax-1 mutant mice also show thymic hypoplasia, these results suggest that Hoxa-3 may be required to maintain pax-1 expression in these cells and that the reduction of pax-1 expression is part of the athymic teleology in Hoxa-3 mutant mice. The thyroid gland is formed from the fusion of two structures of separate embryonic origin, the thyroid diverticulum, which is formed from endodermal epithelium in the floor of the pharynx, and the ultimobranchial body, formed from mesenchymal neural crest in the 4th pharyngeal pouch. Both of these sites express Hoxa-3 and are defective in mutant mice. Often a vesicle is observed in mutant mice that is exclusively composed of calcitonin-producing cells, suggesting the persistence of an ultimobranchial body. Both aspects of the thyroid phenotype show variable expressivity among mutant animals, even on the two sides of the same mutant animal. This variability suggests the presence of a compensating gene or genes, whose utilization is stochastic. A reasonable candidate for providing this compensatory function is the paralogous gene Hoxb-3.

Animals↗
PubMed1994

Targeted disruption of the even-skipped gene, evx1, causes early postimplantation lethality of the mouse conceptus.

Implantation within the mammalian uterus elicits dramatic changes in the growth, differentiation, and morphogenesis of the conceptus. This process is interrupted in mice carrying a targeted disruption of the murine evx1 gene, a homolog of the Drosophila even-skipped (eve) gene. Upon implantation, presumptive evx1- homozygotes elicit a decidual response, invade the uterine epithelium, and attach to the basement membrane between uterine stroma and epithelium, but fail to differentiate extraembryonic tissues or to form egg cylinders prior to resorption. Retrograde analysis of embryo genotypes demonstrates that homozygotes could be isolated as free-floating blastocysts but not as gastrulating egg cylinders. Homozygous mutant blastocysts appeared normal and, when grown in vitro, attach, proliferate, and form trophoblastic giant cells surrounding a growing inner cell mass before rapidly degenerating. In situ hybridization analysis demonstrates evx1 gene expression within the visceral endoderm after implantation and prior to gastrulation, at a time in which the mutant phenotype is first detected.

Animals↗
PubMed1994

Mice with targeted disruptions in the paralogous genes hoxa-3 and hoxd-3 reveal synergistic interactions.

The Hox genes encode transcription factors which mediate the formation of the mammalian body plan along the anteroposterior and appendicular axes. Paralogous Hox genes within the separate linkage groups are closely related with respect to DNA sequence and expression, suggesting that they could have at least partially redundant functions. We showed previously that mice homozygous for independent targeted disruptions in the paralogous genes hoxa-3 and hoxd-3 had no defects in common. But our current analysis of double mutants has revealed strong, dosage-dependent interactions between these genes. We report here that in hoxd-3- homozygotes the first cervical vertebra, the atlas, is homeotically transformed to the adjacent anterior structure. Unexpectedly, in double mutants, rather than observing a more extensive homeotic transformation, the entire atlas is deleted. These observations are interpreted in terms of a model in which these Hox genes differentially regulate the proliferation rates of the appropriate sets of precursor cells.

Animals↗
PubMed1994

Targeted disruptions of the murine Hoxa-4 and Hoxa-6 genes result in homeotic transformations of components of the vertebral column.

It is becoming clear that Hox genes, which encode transcription factors of the Antennapedia homeodomain family, are key players in establishing the body plan of mammalian embryos. They have already been implicated in the formation of the central nervous system, tissues derived from neural crest, the vertebral column and the limbs. In order to examine the roles of hoxa-4 and hoxa-6 during development, mice with targeted disruptions in these genes were generated. Each shows homeotic transformation of cervical vertebrae, at positions that approximate the anterior borders of expression of these genes in the prevertebrae. Defects were not observed in other tissues that normally express these genes. Hoxa-4-/hoxa-4- mice show, with 100% penetrance, anterior transformations of the dorsal aspects of the third cervical vertebra by acquiring features normally associated with the second cervical vertebra. Mice homozygous for the hoxa-6 mutation show, with incomplete penetrance, even on opposite sides of the same animal, posterior transformations of the seventh cervical vertebra to the first thoracic vertebra. In addition, both hoxa-4-/hoxa-4- and hoxa-6-/hoxa-6- mice show variability in expressivity. These data indicate that alternative genetic pathways can partially, and at times completely, substitute for the function of these two genes. Other members of these two paralogous Hox families are good candidates for providing the substitutions. As paralogous genes lie on different chromosomes, it is possible to examine the degree of redundancy among these genes by intercrossing mice with the appropriate individual disruptions. The analysis of double, triple and even quadruple mutants should determine the ways in which these Hox genes interact in order to specify the multitude of tissues in a restricted region of the developing mouse embryo.

Alleles↗
PubMed1994

Axial homeosis and appendicular skeleton defects in mice with a targeted disruption of hoxd-11.

Using gene targeting, we have created mice with a disruption in the homeobox-containing gene hoxd-11. Homozygous mutants are viable and the only outwardly apparent abnormality is male infertility. Skeletons of mutant mice show a homeotic transformation that repatterns the sacrum such that each vertebra adopts the structure of the next most anterior vertebra. Defects are also seen in the bones of the limb, including regional malformations at the distal end of the forelimb affecting the length and structure of phalanges and metacarpals, inappropriate fusions between wrist bones, and defects at the most distal end in the long bones of the radius and ulna. The phenotypes show both incomplete penetrance and variable expressivity. In contrast to the defects observed in the vertebral column, the phenotypes in the appendicular skeleton do not resemble homeotic transformations, but rather regional malformations in the shapes, length and segmentation of bones. Our results are discussed in the context of two other recent gene targeting studies involving the paralogous gene hoxa-11 and another member of the Hox D locus, hoxd-13. The position of these limb deformities reflects the temporal and structural colinearity of the Hox genes, such that inactivation of 3' genes has a more proximal phenotypic boundary (affecting both the zeugopod and autopod of the limb) than that of the more 5' genes (affecting only the autopod). Taken together, these observations suggest an important role for Hox genes in controlling localized growth of those cells that contribute to forming the appendicular skeleton.

Animals↗
PubMed1993

Location of crossovers during gene targeting with insertion and replacement vectors.

Gene targeting was used to introduce nonselectable genetic changes into chromosomal loci in mouse embryo-derived stem cells. The nonselectable markers were linked to a selectable marker in both insertion- and replacement-type vectors, and the transfer of the two elements to the Hprt locus was assayed. When insertion vectors were used as substrates, the frequency of transfer was highly dependent upon the distance between the nonselectable marker and the double-strand break in the vector. A marker located close to the vector ends was frequently lost, suggesting that a double-strand gap repair activity is involved in vector integration. When replacement vectors were used, cotransfer of a selectable marker and a nonselectable marker 3 kb apart was over 50%, suggesting that recombination between vector and target often occurs near the ends of the vector. To illustrate the use of replacement vectors to transfer specific mutations to the genome, we describe targeting of the delta F508 mutation to the CFTR gene in mouse embryo-derived stem cells.

Animals↗
PubMed1993

Mice homozygous for a targeted disruption of the proto-oncogene int-2 have developmental defects in the tail and inner ear.

We derived mice that carry a targeted insertion of a neor gene in the int-2 (Fgf-3) proto-oncogene coding sequences. The mutation was found to be recessive and mice that were homozygous for the insertion did not often survive to adulthood. The mutant mice had defects in the development of the tail and inner ear that could be correlated with disruption of int-2 expression in the posterior primitive streak and hindbrain or otic vesicle. While the tail phenotype was 100% penetrant, we found that the inner ear phenotype had reduced penetrance and variable expressivity. The variable expressivity could not be attributed to variability in the genetic background of the mutant allele or to leaky expression from the mutant allele. Thus, we conclude that even in a uniform genetic background, stochastic variation in the expression of a developmental circuit can result in dramatic differences in phenotypic consequences.

Animals↗
PubMed1993

Loss of Hox-A1 (Hox-1.6) function results in the reorganization of the murine hindbrain.

Targeted disruption of the murine hox-A1 gene results in severe defects in the formation of the hindbrain and associated cranial ganglia and nerves. Carbocyanine dye injections were used to trace afferent and efferent projections to and from the hindbrain in hox-A1-/hox-A1- mutant mice. Defects were observed in the position of efferent neurons in the hindbrain and in their projection patterns. In situ hybridization was used to analyze the transcription pattern of genes expressed within specific rhombomeres. Krox-20, int-2 (fgf-3), and hox-B1 all display aberrant patterns of expression in hox-A1- mutant embryos. The observed morphological and molecular defects suggest that there are changes in the formation of the hindbrain extending from rhombomere 3 through rhombomere 8 including the absence of rhombomere 5. Also, motor neurons identified by their axon projection patterns which would normally be present in the missing rhombomere appear to be respecified to or migrate into adjacent rhombomeres, suggesting a role for hox-A1 in the specification of cell identity and/or cell migration in the hindbrain.

Animals↗
PubMed1993

Mice homozygous for a targeted disruption of Hoxd-3 (Hox-4.1) exhibit anterior transformations of the first and second cervical vertebrae, the atlas and the axis.

Gene targeting in embryo-derived stem (ES) cells was used to generate mice with a disruption in the homeobox-containing gene Hoxd-3 (Hox-4.1). Mice homozygous for this mutation show a radically remodeled craniocervical joint. The anterior arch of the atlas is transformed to an extension of the basioccipital bone of the skull. The lateral masses of the atlas also assume a morphology more closely resembling the exoccipitals and, to a variable extent, fuse with the exoccipitals. Formation of the second cervical vertebra, the axis, is also affected. The dens and the superior facets are deleted, and the axis shows 'atlas-like' characteristics. An unexpected observation is that different parts of the same vertebra are differentially affected by the loss of Hoxd-3 function. Some parts are deleted, others are homeotically transformed to more anterior structures. These observations suggest that one role of Hox genes may be to differentially control the proliferation rates of the mesenchymal condensations that give rise to the vertebral cartilages. Within the mouse Hox complex, paralogous genes not only encode very similar proteins but also often exhibit very similar expression patterns. Therefore, it has been postulated that paralogous Hox genes would perform similar roles. Surprisingly, however, no tissues or structures are affected in common by mutations in the two paralogous genes, Hoxa-3 and Hoxd-3.

Animals↗