Short-tailed Mouse Research Articles

A new endemic species of the subgenus Mus (Rodentia, Mammalia) on the Island of Cyprus

The house mouse (Mus musculus domesticus) and the short-tailed mouse of the eastern Mediterranean area (M. macedonicus) were thought to live sympatrically on Cyprus Island. Recently, a phylogenetic survey has shown that the non-commensal mouse of Cyprus was an unknown sister species of European wild mice. Here, we describe this new species of the genus Mus (Rodentia, Mammalia), namely Mus cypriacus sp. n., based on 19 specimens trapped in the southern part of Cyprus. These animals were first compared to Eurasian species of mice using both molecular genetics (complete D-loop sequences and nuclear gene intron) and cytogenetics to state on its systematic status. Then classical and geometric morphometric analyses on both cranial and dental characters have been performed to compare Mus cypriacus with circum-Mediterranean species and provide diagnositic morphological characters. Genetic data strongly support a sister species relationship of the new species to M. macedonicus, the closest mainland taxon. Morphometric analyses provide satisfying criteria for diagnosis of this species relative to other Mediterranean species. The most obvious phenotypic characteristics are its long tail and the allometric gigantism and shape robustness of its cranial and dental characters compared to other Mediterranean mice. The molecular clock and the history of the murine settlement on Cyprus are congruent and suggest that the common ancestor of M. cypriacus and M. macedonicus arrived on Cyprus during the Middle Pleistocene by a founder event on natural raft. The remoteness of Cyprus through time has prevented introgression from the mainland gene pool, and favoured phenotypic adaptation to competition release, leading to the allopatric speciation of M. cypriacus.

A Novel Murine Gene, Sickle tail, Linked to the Danforth's short tail Locus, Is Required for Normal Development of the Intervertebral Disc

We established the mutant mouse line, B6;CB-SktGtAyu8021IMEG (SktGt), through gene-trap mutagenesis in embryonic stem cells. The novel gene identified, called Sickle tail (Skt), is composed of 19 exons and encodes a protein of 1352 amino acids. Expression of a reporter gene was detected in the notochord during embryogenesis and in the nucleus pulposus of mice. Compression of some of the nuclei pulposi in the intervertebral discs (IVDs) appeared at embryonic day (E) 17.5, resulting in a kinky-tail phenotype showing defects in the nucleus pulposus and annulus fibrosus of IVDs in SktGt/Gt mice. These phenotypes were different from those in Danforth's short tail (Sd) mice in which the nucleus pulposus was totally absent and replaced by peripheral fibers similar to those seen in the annulus fibrosus in all IVDs. The Skt gene maps to the proximal part of mouse chromosome 2, near the Sd locus. The genetic distance between them was 0.95 cM. The number of vertebrae in both [Sd +/+ SktGt] and [Sd SktGt/+ +] compound heterozygotes was less than that of Sd heterozygotes. Furthermore, the enhancer trap locus Etl4lacZ, which was previously reported to be an allele of Sd, was located in the third intron of the Skt gene.

Distribution, habitat and conservation status ofLeggadina lakedownensis(Rodentia: Muridae) in Queensland

The Lakeland Downs Mouse Leggadina lakedownensis is one of two species of short-tailed mice endemic to Australia. In Queensland there have been only very few recent sightings, and the species was thought to be restricted to parts of northern Cape York Peninsula. Five new localities are reported, including range extensions to central Queensland. Habitat for the species varies from chenopod to spinifex grasslands, Melaleuca woodlands and open savanna Eucalyptus woodlands, ranging from tropical coastal esplanades to sub-tropical rangelands. Trap localities encompass altitude from sea level to over 1000 m, and annual rainfall from 600-1800 mm, but are unified by a dense ground cover and waterlogging red or white sandy clays. Some potential threats to these rodent's populations are postulated including loss of ground cover and clearing of habitat in coastal regions. Despite contentions of a plaguing species, this rodent was rarely encountered in areas extensive sampled within its range. Notwithstanding the spa...

Two deeply divergent mitochondrial clades in the wild mouse Mus macedonicus reveal multiple glacial refuges south of Caucasus.

A survey of 77 individuals covering the range of Mus macedonicus from Georgia in the East to Greece and Bulgaria in the West and Israel in the South has shown the existence of two deeply divergent mitochondrial clades. The southern clade was until now undetected and characterises mice from Israel. Nuclear genes also show some amount of regional differentiation tending to separate the southern M. macedonicus from the northern ones. These results point towards the fact that the eastern Mediterranean short-tailed mouse, which was seen as a fairly homogeneous monotypic species, has in fact a more complex phylogeographic history than has been suspected, and that it warrants the existence of two subspecies. The reasons for this non-uniformity probably ought to be looked for in the history of faunal movements linked to glacial periods, underlining the possible existence of at least two refugia south of the Caucasus.

Screening Evaluation of the Ecological Risks to Terrestrial Wildlife Associated with a Coal Ash Disposal Site

Between 1955 and 1989, coal ash was deposited within an impounded watershed on the U.S. Department of Energy's Oak Ridge Reservation in Tennessee, creating the 3.6 ha Filled Coal Ash Pond (FCAP). The site has subsequently become vegetated wildlife habitat. To evaluate risks that metals in ash may pose to wildlife; ash, surface water, small mammal, and vegetation samples were collected and metal residues were determined. Metal concentrations, As and Se in particular, were elevated in ash, surface water, plant foliage, and small mammals relative to reference materials. Estimates of metal exposures were calculated for short-tailed shrews, white-footed mice, white-tailed deer, red fox, and red-tailed hawks. While shrews and mice were assumed to reside exclusively at and receive 100% exposure from the site, exposure experienced by deer, fox, and hawks was assumed to be proportional to the size of the site relative to their home range. Because deer had been observed to consume ash, presumably for its high sodium content, exposure experienced by deer consuming ash to meet sodium requirements was also estimated. Exposure estimates were compared to body-size adjusted toxicity data for each metal. These comparisons suggest that metals at the site may be detrimental to reproduction and survivorship of mice, shrews, and deer consuming ash for sodium; fox and hawks do not appear to be at risk

Diets and predictions of feeding rate of house mice and Lakeland Downs short-tailed mice inhabiting an arid-zone island in Western Australia

An analysis of the faecal pellets of two species of arid-zone mouse, the house mouse (Mus domesticus) and Lakeland Downs short-tailed mouse (Leggadina lakedownensis), inhabiting Thevenard Island in Western Australia was conducted to ascertain their dietary requirements, and to use this information to predict their feeding rates in the field. Both species consumed seed, monocotyledon and dicotyledon plant material and invertebrate material, although the relative frequency-of-occurrence of these items varied throughout the year. Invertebrate material formed the highest proportion of dietary intake for both rodent species at all times, suggesting that this dietary strategy is advantageous for rodent species that inhabit environments where plant seeding is seasonal and rainfall dependent. The dry-matter intake (DMI) of free-ranging M.�domesticus and L. lakedownensis was predicted and compared using information from two sources: their isotopic water fluxes and the water content of their diet, and their isotopic sodium fluxes and the sodium content of their diet with and without corrections for non-dietary (exogenous) sources of sodium. The DMI derived from the water turnover was high for both species, suggesting that the mice were drinking and that assumptions inherent in this calculation were violated. Feeding rates were also high if no correction was made for exogenous, non-dietary sodium. When corrections were made, however, M. domesticus was predicted to ingest 4.62 ± 0.20 g dry matter day–1 compared with 3.86 ± 0.23 g dry matter day–1 for L.�lakedownensis. When DMI was scaled on the basis of allometric predictions for desert eutherians, only estimates of DMI for M. domesticus fell outside the predicted 95% confidence intervals. The results presented suggest that M. domesticus were obtaining some sodium from sources additional to their diet. Taken together, this methodology provides a useful application for measuring the feeding rate of free-ranging species given known dietary requirements in the field.

Evaluation and cost-benefits of controlling house mice ( Mus domesticus) on islands: an example from Thevenard Island, Western Australia

Feral mammals occur on many offshore islands around Australia, but their eradication by poison-baiting requires a careful assessment of the associated costs and long-term benefits. This paper describes a replicated trial program to poison house mice Mus domesticus selectively on Thevenard Island, Western Australia, in the presence of a native species of mouse, and to evaluate whether the eradication of house mice from the island is an achievable and cost-effective goal. It was found the densities and survivorship of house mice declined more on grids with bait stations spaced every 10 m than on grids baited every 20 m when compared to unbaited (control) grids. On one grid baited every 10 m, the abundance of house mice declined by 83% 22 days after baiting commenced. This decline was correlated with an increase in the abundance of short-tailed mice Leggadina lakedownensis on the grid. A total of 55 person days was required to conduct the present poison-baiting trials, and expenses incurred were over $AUS1000 ha −1. Baiting islands for house mice can prove a costly excercise, and management organisations need to assess whether ground-based baiting is an efficacious and cost-effective management option if complete eradication fails.

Population structure and dynamics of sympatric house mice, Mus domesticus, and Lakeland Downs short-tailed mice, Leggadina lakedownensis, on Thevenard Island, Western Australia

A trapping study from 1994 to 1996 examined the population structure and dynamics of two sympatric populations of rodent, Mus domesticus and Leggadina lakedownensis, inhabiting an island off the coast of Western Australia. Population abundance fluctuated dramatically within and between years for both species, and those of M. domesticuswere influenced by cyclones that passed close to the island. Population densities for M. domesticus reached 13.4 mice ha–1 in November 1995, and were always twice those of L. lakedownensis. M. domesticus bred throughout the year. In contrast, the breeding season for L. lakedownensis was strictly seasonal, and was restricted to the mid-year months. Numbers of M. domesticus were correlated with rainfall that fell 3–6 months previously. Similarly, numbers of L. lakedownensis were correlated with rain that fell 3 months previously. Although no significant relationship was detected between total invertebrate and mouse abundance, numbers of M. domesticus were correlated with those of lepidopteran larvae collected in pitfall traps. These data suggest that species coexistence on the island may be mediated by extreme rainfall events, and a lack of competition during low population densities.

Movements and refugia of Lakeland Downs short-tailed mice, Leggadina lakedownensis, and house mice, Mus domesticus, on Thevenard Island, Western Australia

Radio-telemetry was used to identify the home range and refuge sites of two species of mouse inhabiting a semi-arid island off the Western Australian coast, in an effort to understand differences in their water metabolism. The native short-tailed mouse, Leggadina lakedownensis, had a median home range of 4.8 ha. This area increased during the non-breeding season (5.3 ha) compared with the breeding season (3.0 ha), but this difference was not significant. In contrast, the median home range for the house mouse, Mus domesticus, was smaller (2.8 ha), although this was variable. Core areas were best represented by the 75% and 60% isopleths for M. domesticus and L. lakedownensis, respectively. Core areas were greater in L. lakedownensis (1.0 ha) than in M. domesticus (0.8 ha). Furthermore, the degree of overlap in core areas was low for L. lakedownensis, but absent for M. domesticus. There was no evidence that M. domesticus used burrows as refuges. Instead, they sheltered in dense bushes above ground during the day where air temperatures were ameliorated by the cover. L. lakedownensis rested in burrows during the day where high air temperatures were mainatined at a constant 28°C, and a relative humidity of between 72–97%. Burrow morphology was simple and comprised two types: burrows with a single chamber, and those without a chamber, indicative of a solitary habit. These results suggest that a fossorial behaviour in L. lakedownensis may lower its water economy compared with M. domesticus, which shelters above ground.

Water and sodium balances and metabolic physiology of house mice (Mus domesticus) and short-tailed mice (Leggadina lakedownensis) under laboratory conditions.

A laboratory study investigated the metabolic physiology, and response to variable periods of water and sodium supply, of two arid-zone rodents, the house mouse (Mus domesticus) and the Lakeland Downs short-tailed mouse (Leggadina lakedownensis) under controlled conditions. Fractional water fluxes for M. domesticus (24 +/- 0.8%) were significantly higher than those of L. lakedownensis (17 +/- 0.7%) when provided with food ad libitum. In addition, the amount of water produced by M. domesticus and by L. lakedownensis from metabolic processes (1.3 +/- 0.4 ml.day-1 and 1.2 +/- 0.4 ml.day-1, respectively) was insufficient to provide them with their minimum water requirement (1.4 +/- 0.2 ml.day-1 and 2.0 +/- 0.3 ml.day-1, respectively). For both species of rodent, evaporative water loss was lowest at 25 degrees C, but remained significantly higher in M. domesticus (1.1 +/- 0.1 mg H2O.g-0.122.h-1) than in L. lakedownensis (0.6 +/- 0.1 mg H2O.g-0.122.h-1). When deprived of drinking water, mice of both species initially lost body mass, but regained it within 18 days following an increase in the amount of seed consumed. Both species were capable of drinking water of variable saline concentrations up to 1 mol.l-1, and compensated for the increased sodium in the water by excreting more urine to remove the sodium. Basal metabolic rate was significantly higher in M. domesticus (3.3 +/- 0.2 mg O2.g-0.75.h-1) than in L. lakedownensis (2.5 +/- 0.1 mg O2.g-0.75.h-1). The study provides good evidence that water flux differences between M. domesticus and L. lakedownensis in the field are due to a requirement for more water in M. domesticus to mect their physiological and metabolic demands. Sodium fluxes were lower than those observed in free-ranging mice, whose relatively high sodium fluxes may reflect sodium associated with available food.

Anorectal malformations associated with enteric dysganglionosis in Danforth's short tail (Sd) mice

Background: The spontaneous mutant Danforth's short tail (Sd) mouse has been studied over the last 60 years from the morphological, embryological, and genetic point of view. The Sd mutation affects a gene essential to notochordal development, and the Sd mouse phenotype represents an analogue of human caudal regression syndrome. The Sd Sd mouse presents different types of anorectal malformations (ARM) and was suggested as a simple and cheap model of investigation of ARM morphology and embryology. In the current study, the Sd mouse enteric nervous system (ENS) was thoroughly investigated with specific immunohistochemical markers. Methods: Macroscopic analysis, normal histology, and immunohistochemical techniques for detecting neurofilaments (NF) and NOS 1 were used to study ENS of 138 Sd mice and 25 controls. Results: The surprising results of this study showed that Sd mutation is associated with different degrees of hypoganglionosis and aganglionosis. In 41% of Sd SD -affected mice, the rectal pouch was aganglionic and in the remaining 58% was severely hypoganglionic. In addition, 4.1% of heterozygous mice presented a distal aganglionosis and 8.3% hypoganglionsis. Conclusions: These results suggest that Sd mutation independently affects distinct cell lines during early organogenesis, as notochord cells, ventral hingut endoderm, and neuroblasts migrating from neural crest cells. Comparing the Sd murine model with human pathology, this study confirms that the association between ARM and intestinal dysganglionosis is not rare and underlines the importance of detecting in every ARM patient the innervation abnormalities of rectal pouch and fistulas.

Murine viruses in an island population of introduced house mice and endemic short-tailed mice in Western Australia.

House mice (Mus domesticus) were recently introduced to Thevenard Island, off the northwest coast of Western Australia. This island is also habitat for an endangered native rodent, the short-tailed mouse (Leggadina lakedownensis). Concerns have been raised that house mice may pose a threat to L. lakedownensis both through competition and as a source of infection. To assess the threat to L. lakedownensis posed by viral pathogens from M. domesticus, a serological survey was conducted from 1994 to 1996 of both species for evidence of infection with 14 common murine viruses (mouse hepatitis virus, murine cytomegalovirus, lymphocytic choriomeningitis virus, ectromelia virus, mouse adenovirus strains FL and K87, minute virus of mice, mouse parvovirus, reovirus type 3, Sendai virus, Theiler's mouse encephalomyelitis virus, polyoma virus, pneumonia virus of mice, and encephalomyocarditis virus) and Mycoplasma pulmonis. Despite previous evidence that populations of free-living M. domesticus from various locations on the Australian mainland were infected with up to eight viruses, M. domesticus on Thevenard Island were seropositive only to murine cytomegalovirus (MCMV). Antibodies to MCMV were detected in this species at all times of sampling, although seroprevalence varied. Infectious MCMV could be isolated in culture of salivary gland homogenates from seropositive mice. In contrast, L. lakedownensis on Thevenard Island showed no serological evidence of infection with MCMV, any of the other murine viruses, or M. Pulmonis, and no virus could be isolated in culture from salivary gland homogenates. Although MCMV replicated to high titers in experimentally infected inbred BALB/c laboratory mice as expected, it did not replicate in the target organs of experimentally inoculated L. lakedownensis, indicating that the strict host specificity of MCMV may prevent its infection of L. lakedownensis. These results suggest that native mice on Thevenard Island are not at risk of MCMV infection from introduced house mice, and raise interesting questions about the possible selective survival of MCMV in small isolated populations of M. domesticus.

Kidney Structure in Two Species of Arid Zone Rodent: Lakeland Downs Short-Tailed Mouse, Leggadina lakedownensis, and the House Mouse, Mus domesticus

Native rodents that inhabit the arid zones of Australia produce amongst the most concentrated urines recorded in an effort to conserve water during periods when it is scarce (Mac MiiJen and Lee 1967; Hewitt 1981). Their ability to survive in the absence of free water has been inherently associated with the morphology of their kidneys. Sperber (1944) developed the relative medullary thickness (RMT) index to compare the size of the medulla, and hence the concentrating ability of the kidney among mammalian species. This concept was extended further by Schmidt-Nielsen and O'Dell (1961) and later by Greenwald (1989) and Beuchat (1990), who compared absolute and RMT with the maximum urine osmolality of mammals.

Apoptosis of Epaxial Myotome inDanforth's short-tail(Sd) Mice in Somites That Form Following Notochord Degeneration

Danforth's short-tail(Sd) mouse is a semidominant mutation that prevents completion of notochord development. In homozygous mutant mice, the notochord completely degenerates at embryonic day 9.5 (E9.5), whereas the neural tube and somites continue to form, permitting analysis of somite development in the absence of inductive signals from the notochord and floor plate. In the somites formed after notochord degeneration,Myf5expression initiates in a normal temporal sequence, but instead of the normal restriction to the dorsomedial somite, its expression extends into the ventral somite.MyoD, myogenin,andmyosin heavy chainare normally expressed in the ventral myotome and there is normal development of hypaxial muscles. In contrast, subsequent to initialMyf5expression, muscle gene expression was not detected in the dorsal myotome and a high level of apoptosis was observed with significantly decreased formation of epaxial muscles. The apoptosis of epaxial muscle in somites that formed after notochord degeneration is consistent with a role for the notochord in the survival and differentiation of the dorsal myotome.

The Thevenard Island mouse: historic and conservation implications from mitochondrial DNA sequence-variation

The level of mitochondrial differentiation between Thevenard Island and mainland populations of the short-tailed mice Leggadina lakedownensis was determined using DNA sequencing of the Control Region. Using temperature gradient gel electrophoresis, outgroup heteroduplex analysis detected eight haplotypes. These were sequenced for 362 basepairs. Our results show that the Thevenard Island Short-tailed Mouse is indeed L. lakedownensis, and is most closely related to L. lakedownensis in the Pilbara in Western Australia. Together, Thevenard Island and adjacent mainland populations are sufficiently divergent from those in northern Australia as to be recognized as two clearly distinct mitochondrial DNA lineages. Conservation and taxonomic implications arising from a phylogeny of haplotypes suggest that two Management Units exist within L. lakedownensis ? a northern unit that includes individuals from the Kimberley (Western Australia) to Kakadu National Park (Northern Territory), and a western unit comprising individuals from Thevenard Island and the Pilbara (Western Australia). These conservation units should be managed as separate subspecies of L. lakedownensis, and a high conservation priority should be given to the Thevenard Island population because it provides an important refugium for L. lakedownensis not just in the Pilbara, but in Australia.

Mutation watch: mouse brachyury (T), the T-box gene family, and human disease.

The classical mouse mutation brachyury (‘‘short tail’’), first described in 1927, is located in the T/t region of proximal mouse Chromosome (Chr) 17. Heterozygotes for null alleles of brachyury have short tails and mild skeletal defects due to haploinsufficiency. Homozygous null mice have a severe developmental disorder that includes defective mesoderm formation and regression of the notochord, and they do not survive beyond E10. Seventy years of work on the short tail mouse has resulted in isolation of an important family of transcriptional regulators of early development, as well as the recent identification of the genes responsible for two complex human developmental disorders: the Holt-Oram syndrome of cardiac and limb defects, and the ulnar-mammary syndrome affecting limb, tooth, and genital development.

Localization of extracellular matrix molecules, integrins and their regulators, TGF βs, is correlated with axon pathfinding in the spinal cord of normal and Danforth's short tail mice

To clarify the roles of extracellular matrix molecules (ECMs) and their receptors, integrins, in axonal pathfinding, their spatiotemporal localization was studied immunohistochemically in the developing mouse spinal cord. Immunoreactivities for collagen type IV (Col IV), laminin, integrins (α2, α3 and β1 subunits), and transforming growth factor (TGF) βs (TGF β2 and TGF β3), putative regulators of gene expression of these molecules, were localized on the midline of the ventral spinal cord, or the `floor plate', in normal ICR mice. These immunoreactions appeared at embryonic day 9 (E9), when commissural axons began to cross the floor plate, and peaked at E13–E14 when more axons crossed, turned rostrally, and projected longitudinally. At this stage, TAG-1-immunopositive commissural axons passed through the floor plate region. Longitudinal axons, on the other hand, projected ipsilaterally parallel to the midline. Immunoreactions for ECMs, integrins and TGF βs were weakly positive at the midline until postnatal day 0 (P0), after which they decreased markedly. In Danforth's short tail ( Sd) heterozygous mutants with discontinuous floor plates, immunoreactions for ECMs, integrins, and TGF βs were not detected at P0. Few crossing axons were seen at this stage, and longitudinally ascending axons crossed via aberrant paths in these regions. These results suggest that the restricted localization of ECMs, integrins, and TGF βs at the floor plate is involved in the pathfinding of commissural and longitudinal axons.

Proteoglycans are required for maintenance of Wnt-11 expression in the ureter tips.

Development of the metanephric kidney requires the concerted interaction of two tissues, the epithelium of the ureteric duct and the metanephric mesenchyme. Signals from the ureter induce the metanephric mesenchyme to condense and proliferate around the ureter tip, reciprocal signals from the mesenchyme induce the ureter tip to grow and to branch. Wnt genes encode secreted glycoproteins, which are candidate mediators of these signaling events. We have identified three Wnt genes with specific, non-overlapping expression patterns in the metanephric kidney, Wnt-4, Wnt-7b and Wnt-11. Wnt-4 is expressed in the condensing mesenchyme and the comma- and S-shaped bodies. Wnt-7b is expressed in the collecting duct epithelium from 13.5 days post coitum onward. Wnt-1l is first expressed in the nephric duct adjacent to the metanephric blastema prior to the outgrowth of the ureteric bud. Wnt-l1 expression in Danforth's short-tail mice suggests that signaling from the mesenchyme may regulate Wnt-ll activation. During metanephric development, Wnt-11 expression is confined to the tips of the branching ureter. Maintenance of this expression is independent of Wnt-4 signaling and mature mesenchymal elements in the kidney. Moreover, Wnt-ll expression is maintained in recombinants between ureter and lung mesenchyme suggesting that branching morphogenesis and maintenance of Wnt-ll expression are independent of metanephric mesenchyme-specific factors. Interference with proteoglycan synthesis leads to loss of Wnt-ll expression in the ureter tip. We suggest that Wnt-11 acts as an autocrine factor within the ureter epithelium and that its expression is regulated at least in part by proteoglycans.

Annexin IV is a marker of roof and floor plate development in the murine CNS

Midline structures, such as the notochord and floor plate, are crucial to the developing central nervous system (CNS). Previously, we demonstrated that annexin IV is an excellent marker of midline structures. In the present study, we explore the possible role of annexin IV in development of the CNS midline. Using immunocytochemistry with an antibody to annexin IV, we have elucidated the temporal and spatial expression of this molecule. Annexin IV is present in the notochord at embryonic day (E) 8.5, prior to its expression in any structures within the neural tube. Subsequently, annexin IV is expressed by floor plate cells at E9.5. Annexin IV is also expressed in the roof plate, but not until E10.5. To determine if normal morphogenesis of these midline structures is essential for annexin IV expression, we analyzed two strains of mutant mice that have defective formation of either the floor or the roof plate. In Danforth's short-tail mice, the floor plate is absent from the caudal spinal cord, and annexin IV immunopositivity disappears at the level where the floor plate is missing. In curly tail mutant mice, there can be a failure of the neural tube to close, and in these regions there is no annexin IV expression in presumptive roof plate cells. Finally, annexin IV immunolabeling is present from the caudal spinal cord, through the brainstem up to the diencephalon and lamina terminalis. Thus, annexin IV is an excellent marker for differentiated midline cells, is temporally and spatially correlated with development of the floor and roof plates, and is expressed in a rostral-caudal manner that supports the hypothesis that the floor plate extends the full length of the original neural tube.

Characterization and Developmental Expression of Pax9, a Paired-Box-Containing Gene Related to Pax1

Pax9, a recently identified mouse paired-box-containing gene, is highly homologous to Pax1 and belongs to the same subfamily as Pax1, Hup48, PAX9, and pox meso. Two overlapping cDNA clones spanning the entire coding region of Pax9 were isolated and sequenced. A comparison of the Pax1 and -9 protein sequences reveals a high degree of similarity even outside the paired box, while the carboxy-terminus of the two proteins diverges completely. We demonstrate that Pax9 can bind to the e5 sequence from the Drosophila even skipped promoter, which is also recognized by Pax1. We analyzed the expression of Pax9 during embryo-genesis of wildtype, Undulated short-tail ( Un s), and Danforth's short tail ( Sd) mice. In wildtype embryos Pax9 is expressed in the pharyngeal pouches and their derivatives, the developing vertebral column, the tail, the head, and the limbs. Expression of Pax9 is unaffected in Un s embryos, in which the Pax1 gene is deleted, arguing that expression of Pax9 is not dependent on Pax1. The expression of Pax9 is lost in the caudal part of Sd homozygous embryos, suggesting that expression of Pax9 in the vertebral column independent on the notochord. These results indicate that both Pax9 and - 1 may act in parallel during morphogenesis of the vertebral column.