Embryonic and postnatal development of masticatory and tongue muscles

This review summarizes findings concerning the unique developmental characteristics of mouse head muscles (mainly the masticatory and tongue muscles) and compares their characteristics with those of other muscles. The developmental origin of the masticatory muscles is the somitomeres, whereas the tongue and other muscles, such as the trunk (deep muscles of the back, body wall muscles) and limb muscles, originate from the somites. The program controlling the early stages of masticatory myogenesis, such as the specification and migration of muscle progenitor cells, is distinctly different from those in trunk and limb myogenesis. Tongue myogenesis follows a similar regulatory program to that for limb myogenesis. Myogenesis and synaptogenesis in the masticatory muscles are delayed in comparison with other muscles and are not complete even at birth, whereas the development of tongue muscles proceeds faster than those of other muscles and ends at around birth. The regulatory programs for masticatory and tongue myogenesis seem to depend on the developmental origins of the muscles, i.e., the origin being either a somite or somitomere, whereas myogenesis and synaptogenesis seem to progress to serve the functional requirements of the masticatory and tongue muscles.

Effects of diet consistency on the expression of insulin-like growth factors (IGFs), IGF receptors and IGF binding proteins during the development of rat masseter muscle soon after weaning

A soft diet facilitates the development of faster-type fibres in rat masseter muscle in the 9 days after weaning compared with a hard diet. To determine whether insulin-like growth factors (IGFs), IGF receptors (IGFRs) and IGF binding proteins (IGFBPs) are involved in this fibre-type alteration, the expression of myosin heavy chain (MHC), IGF, IGFR and IGFBP mRNAs in the masseter muscle of rats fed a hard or soft diet for 9 days after weaning was analysed using competitive, reverse transcriptase-polymerase chain reaction. A soft diet decreased the expression of MHC IIa (slower type) by 70%, but increased the expression of MHC IIx (intermediate type) and IIb (faster type) by 80 and 582%, respectively, compared with a hard diet. These findings verified that a soft diet facilitates the development of faster-type fibres in rat masseter muscle compared with a hard diet. A soft diet induced reductions of 25-76% (P < 0.05-0.01) in the expression of IGF-I, IGF-II, IGFR2, IGFBP4 and IGFBP6 compared with a hard diet, but induced a 25% (P < 0.05) increase only in expression of IGFBP3. These findings suggest that the changes in expression of IGF-I, IGF-II, IGFR2, IGFBP3, IGFBP4 and IGFBP6 are associated with the fibre-type alteration of rat masseter muscle in response to diet consistency soon after weaning.

Smart probe: a novel fluorescence quenching-based oligonucleotide probe carrying a fluorophore and an intercalator

A novel probe (Smart probe) has been developed for nucleic acid detection. The smart probe is an oligodeoxyribonucleotide carrying a fluorophore and an intercalator internally. Fluorescence of the smart probe is quenched by the intercalator in the absence of target sequence. While upon hybridization the probe emits greater fluorescence due to the interference of quenching by intercalation. The smart probe has been shown to recognize a single base mismatch in the double-stranded form without utilizing thermal stability difference of hybrids.

MagiProbe: a novel fluorescence quenching-based oligonucleotide probe carrying a fluorophore and an intercalator (II)

MagiProbe is a fluorescence quenching-based oligonucleotide probe and applicable to homogeneous nucleic acid assays. Further advantage of this probe is its inherent ability to discriminate between matched and mismatched duplex without reliance on the difference of thermal stability. To improve discriminating ability, the relationships between a position of mismatch in MagiProbe and a power of discrimination were studied. This resulted that intercalation of pyrene was destabilized by a mismatch but still stabilized by neighboring matched base pairs. To afford multiplexing capacity of nucleic acid detection assays to MagiProbe, a variety of differently colored fluorophores were tested in this system. Although each fluorophore showed a different response to hybridization, a couple of promising fluorophores were founded.

Postnatal changes in the nicotinic acetylcholine receptor subunits in rat masseter muscle

No published study on synaptogenesis in masseter muscle has focused on the shift of nicotinic acetylcholine receptors (nAChRs) from the embryonic type (alpha(2)-, beta-, gamma- and delta-subunits) to the adult-type (alpha(2)-, beta-, epsilon- and delta-subunits) and the elimination of nAChRs outside the neuromuscular junction. To identify the time course of the nAChR transitions in rat masseter muscle between 1 and 63 days of age, the expression of delta-, epsilon- and gamma-subunit mRNAs was analysed by competitive polymerase chain reaction in combination with reverse transcription. The expression of the delta-subunit was high between 1 and 7 days of age, then decreased by 95% (P<0.0001) between 7 and 28 days, suggesting that the nAChR elimination occurs during this period. The quantity of the epsilon-subunit increased by approximately 600% (P<0.0001) between 1 and 21 days of age, whereas the quantity of the gamma-subunit decreased by 85% (P<0.0001) during the same period. This result indicates that the nAChR type shift is terminated at 21 days of age. The feeding behaviour of the rats inevitably changed from suckling to biting after 19 days of age, because they were weaned at that age. As the nAChR type shift was terminated soon after weaning, the termination could be related to the change in feeding behaviour. However, it might also be the case that nAChR elimination is not directly related to the change in feeding behaviour, as the elimination continued at the same rate for 9 days after weaning (from 19 to 28 days of age).

Effects of diet consistency on the myosin heavy chain mRNAs of rat masseter muscle during postnatal development

To study the effects of diet consistency on the fiber phenotypes of rat masseter (1-70 days of age), the mRNAs of myosin heavy chain isoforms (MHC embryonic, neonatal, I, IIa, IId/x and IIb) were measured in total RNA preparations from masseters of hard-diet group (HDG) and soft-diet group (SDG) by competitive reverse transcriptase-polymerase chain reaction (RT-PCR). With respect to the time course of the transition of each MHC mRNA expressed as a percentage relative to the maximum mean, the soft diet facilitated early (9 days after weaning) expression of IId/x and IIb isoforms, and also a decline in the expression of neonatal and IIa isoforms. The expression of neonatal, IIa and IId/x isoforms at 70 days of age was significantly (P<0.05, P<0.01, P<0.01, respectively) lower in SDG than in HDG, indicating a higher relative composition of the IIb isoform in the SDG. Embryonic MHC mRNA had disappeared by 14 days of age (i.e. before weaning at 19 days). No MHC I mRNA was observed in any masseter studied. These results suggest that in the rat a soft diet facilitates an even more MHC IIb-rich phenotype in the masseter muscle than a hard diet.

X chromosome methylation-based chimerism assay for sex-mismatched hematopoietic stem cell transplantation

Analysis of hematopoietic chimerism is important for monitoring engraftment, graft failure, and disease recurrence. Although several techniques are now available, their sensitivity is unsatisfactory. In sex-mismatched stem cell transplantation (SCT) with a female donor, Y chromosome-specific sequences have proven the most sensitive marker. However, in the case of a male donor, no such reliable marker has been available to date. In this study, we report a novel method we developed to detect microchimerism in female recipients who receive SCT from male donors. The X-linked human androgen receptor gene (HUMARA) contains a highly polymorphic CAG trinucleotide repeat. Near this polymorphic site are methyl-sensitive HpaII restriction enzyme sites. After HpaII digestion, unmethylated male HUMARA sequences are completely digested, while methylated female ones remain intact among the male origin cells. This allows a highly efficient detection of a small number of female cells. Combined with the nested PCR technique, the X chromosome methylation-based chimerism assay could attain a 10(-4) level of sensitivity, which is 1000-fold higher than that of conventional assays. The applicability of the method was confirmed in two transplant cases. This highly sensitive method can also be applied to detect minimal residual disease or microchimerism in conditions other than hematopoietic SCT.

Analysis of the distribution of CAG repeats and X-chromosome inactivation status of HUMARA gene in healthy female subjects using improved fluorescence-based assay

We investigated the polymorphic CAG-repeat distribution and the X-inactivation status of the human androgen receptor (HUMARA) gene in 58 female Japanese volunteers. Polymerase chain reaction amplification was performed using a fluorescent-dye-labeled primer under conditions specific for GC-rich targets, and fragments were analyzed. To estimate the length of these fragments, FAM-labeled (blue fluorescent) products were simultaneously compared with ROM-labeled size markers (red) that were created by sequencing various HUMARA fragments. The number of polymorphic CAG repeats of HUMARA in 116 alleles from 58 female subjects ranged from 15 to 28. Of the 58 volunteers, 51 (88.0%) were heterozygous. In 96% of the heterozygous female subjects, the allelic differences were no greater than 6 repeats. X-chromosome inactivation was calculated as the ratio of the area of the smaller peak to the sum of the areas of the smaller and larger peaks. The average ratio was 0.38 (range, 0.09-0.50). Preferential use of 1 allele, by more than 75% (ratio. <0.25). was observed in 5 volunteers (10.9%). The clonal nature of a patient with chronic myelogenous leukemia was easily identified. This method is sensitive enough to discriminate a difference of 1 triplet repeat.

Developmental changes in the nicotinic acetylcholine receptor in mouse tongue striated muscle

There are no published studies on synaptogenesis focusing on the elimination of the superfluous nicotinic acetylcholine receptor (nAChR) outside the neuromuscular junction and the nAChR subunit switch from the embryonic-type (alpha2betagammadelta subunits) to the adult-type (alpha2betaepsilondelta subunits) in mouse tongues. To identify the time course of nAChR subunit elimination and switch, we analyzed the expression levels of alpha, epsilon, and gamma subunit mRNAs, and the immunolocalization of the delta subunit protein in the mouse tongue and corresponding hind limb. The analysis included the period from embryonic day (E) 11 to the newborn stage. The nAChR elimination and subunit switch began at E15 in the tongue and at E17 in the hind limb. They were nearly complete at birth in the tongue, but not in the hind limb. The early completion of synaptogenesis in the tongue at birth may be related to the early functional demands placed on the tongue, such as suckling and swallowing, immediately after birth.

Induction of amelogenin and ameloblastin by insulin and insulin-like growth factors (IGF-I and IGF-II) during embryonic mouse tooth development in vitro

Insulin and insulin-like growth factors (IGF-I and IGF-II) are considered pleiotropic, acting as both mitogen and differentiation factors. Several investigators have demonstrated the expression of insulin, IGFs, their cognate receptors and IGF binding proteins during tooth morphogenesis. Previous work done in our laboratory indicated that exogenous insulin and IGFs induce the accumulation of enamel extracellular matrix on mouse mandibular molars cultured in a serumless, chemically defined medium. In order to determine the level of control of these factors in the induction of enamel biomineralization, we designed experiments to quantitate mRNAs for enamel specific-gene products. Mandibular first molars (MI) obtained from E15 Swiss Webster mice were placed in organ culture in the presence of insulin (1,000 ng/ml), IGF-I (100 ng/ml) or IGF-II (100 ng/ml) for 6, 12 and 18-days. At termination date, the RNA was extracted and the concentration of mRNAs for amelogenin, tuftelin and ameloblastin were determined using a quantitative competitive reverse transcription-polymerase chain reaction (RT-PCR) technique (PCR mimic). Our results showed that after 6-days in culture; treatment with insulin, IGF-I and IGF-II increased the synthesis of amelogenin and ameloblastin. In contrast, the expression of tuftelin mRNA was not affected by either factor. In conclusion, our studies showed that the increase in enamel matrix formation by overexpression of IGFs is the result of transcriptional regulation of enamel specific proteins like amelogenin and ameloblastin but not tuftelin. These studies also suggest that the regulatory mechanisms controlling tuftelin gene expression are different than the mechanisms regulating ameloblastin and amelogenin transcription.

Quantitative changes in the mRNA for contractile proteins and metabolic enzymes in masseter muscle of bite-opened rats

To study the effects of bite opening on the fibre phenotypes of rat masseter, the mRNAs of four predominant myosin heavy-chain isoforms (MHC I, IIa, IId/x and IIb) and two alkali light-chain isoforms (LC1f and 3f) as well as those of two metabolic enzymes, carbonic anhydrase III (CAIII, oxidative enzyme) and glucose-phosphate isomerase (GPI, glycolytic enzyme), were measured in relation to the total RNA of masseter muscle by competitive, reverse transcriptase-polymerase chain reaction in control and bite-opened rats. Bite opening (2.8 mm increase in the vertical dimension for 1 week) significantly (P<0.05) increased the amount of MHC IIa mRNA but decreased (P<0.001) the amount of MHC IIb mRNA without changing the amount of MHC IId/x mRNA. No MHC I mRNA was found in any masseter studied. A significant (P<0.01) increase in the mRNA of LC1f associated with a decrease (P<0.05) in that of LC3f was observed after the bite opening. The CAIII mRNA increased significantly (P<0.001), while the GPI mRNA decreased (P<0.05) in association with the bite opening. These results strongly suggest that in 1 week of bite opening changes the rat masseter muscle from a glycolytic, MHC IIb-LC3f-dominant fibre to an oxidative, MHC IIa-LC1f-dominant fibre.

Delayed embryonic development of mouse masseter muscle correlates with delayed MyoD family expression

While the masseter muscle is known to have several unique developmental characteristics as compared with other skeletal muscles, little is known about its myogenesis. Thus, we examined the expression of myogenic marker and of myoD family gene mRNA from embryonic day (E) 11 to birth. The obtained results were compared with our earlier results of the mouse tongue muscle, which is also involved in oral functions. The mRNA quantities were determined by means of the reverse-transcription and competitive-polymerase chain-reaction techniques. The expression of myogenic marker mRNA indicated that differentiation and maturation in the masseter began at E13 as in the tongue, and were not yet completed at birth, although they were completed in the tongue. The expression of myoD, myogenin, and myf5 mRNA peaked later in the masseter (E17) than in the tongue (E13). The expression of MRF4 mRNA began later in the masseter (E15) than in the tongue (E13). These results suggest that the delayed expression of the myoD family genes in the masseter correlates with delayed differentiation and maturation, probably due to the later functional requirements of the masseter than of the tongue.

New polymorphisms of human CD80 and CD86: lack of association with rheumatoid arthritis and systemic lupus erythematosus

The crucial role of costimulatory molecules, CD28, CTLA-4, CD80 and CD86, for T cell activation and inhibition has been established. In the previous study, we reported the results of a polymorphism screening of human CTLA-4 gene. In this study, we screened for polymorphisms of human CD28, CD80 and CD86 genes, and detected that polymorphisms were tested for the association with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Variations were identified in the coding regions of CD80 (452G/A, 614C/G and 864A/G) and CD86 (1057A/G), while no variation was observed in the coding region of CD28. The variations at CD80 position 452 and CD86 position 1057 were present in a substantial proportion of the Japanese population, and were considered to be single nucleotide polymorphisms within the coding sequence (cSNPs). CD80 864 (G-->A) leads to the amino acid substitution N186D, and CD86 1057 (A-->G) results in A304T substitution. Furthermore, in the analysis of CD80 5'-flanking region, six SNPs, -454C/A, -387T/C, -232G/A, -79G/C, -7T/C and /A, and one insertion, -558ins (CATGA), were identified. The combination of these variations was found to constitute four promoter alleles of CD80. None of the observed variations was significantly associated with RA or SLE. Further studies will be of particular interest to examine the functional difference of the promoter alleles for the transcriptional activity of CD80, as well as the evolutionary pathway of the four alleles.

Identification of a novel bacterial sequence associated with Crohn's disease

BACKGROUND & AIMS

Enteric microorganisms are implicated in the pathogenesis of Crohn's disease (CD), but no clear bacterial or viral species has been identified. In this study, representational difference analysis (RDA) was used to isolate DNA segments preferentially abundant in lamina propria mononuclear cells of lesional mucosa vs. adjacent uninvolved mucosa.

METHODS

Two RDA-derived microbial sequences were isolated (I1 and I2) and identified as novel homologues of the ptxR and tetR bacterial transcription-factor families.

RESULTS

Quantitative competitive polymerase chain reaction of paraffin-embedded intestinal specimens from 212 patients showed that I2 DNA was present in many CD colonic lesions (43%), but was infrequent in other colonic specimens (9% of ulcerative colitis lesions and 5% of non-inflammatory bowel disease diseases; P<0.0001). I2 was prevalent in ileal specimens, regardless of disease status (43%-54%). Enzyme-linked immunosorbent assay analysis of 150 individuals with an I2 glutathione-S-transferase fusion protein showed frequent immunoglobulin A seroreactivity in CD (54% of patients), but infrequent seroreactivity in patients with ulcerative colitis, other inflammatory enteric diseases, or normals (10%, 19%, and 4%, respectively; P<0.001 to 0.00001).

CONCLUSIONS

These findings relate CD to a novel lesion-localized and immunologically associated bacterial sequence, suggesting that the microorganism expressing the I2 gene product may be related to CD pathogenesis.

Determination of granulocyte-specific antigens on neutrophil FcA receptor IIIb by PCR-preferential homoduplex formation assay, and gene frequencies in the Japanese population

BACKGROUND AND OBJECTIVES

Granulocyte-specific antigens play an important role in provoking immune neutropenia and transfusion reactions. We developed a new DNA-typing method, PCR-preferential homoduplex formation assay (PHFA), to determine granulocyte-specific antigens on the neutrophil Fcgamma receptor IIIb (FcgammaRIIIb, CD16b), namely, the NA1, NA2, and SH antigens and their gene frequencies in the Japanese population.

MATERIALS AND METHODS

Four hundred unrelated healthy Japanese blood donors were typed using PCR-PHFA. To confirm the accuracy of the results of FcgammaRIIIB genotyping using PCR-PHFA, PCR-sequence-specific primer (SSP) typing and PCR-restriction fragment length polymorphism (RFLP) typing were carried out in another 20 samples for comparison.

RESULTS

The results of PCR-PHFA typing agreed well with other methods. The frequencies of the FcgammaRIIIB alleles were 62.2, 37.8, 0 and 0% for NA1, NA2, SH, and 'NA-null', respectively.

CONCLUSION

The PCR-PHFA method can be semi-automated easily with computer-based assignment and is suitable for typing both small and large numbers of samples. In the Japanese population, the frequency of NA1 is about double that in Caucasians (32.5%), and the SH allele is rare.

Expression of myogenic regulatory factors during the development of mouse tongue striated muscle

While the role of myogenic regulatory factors (MRFs) in skeletal myogenesis has been well evaluated in limb and trunk muscles, very little is known about their role in tongue myogenesis. Here the expression of MRF mRNA in mouse tongue muscle was examined during development from embryonic day (E)11 to birth and compared them with that in hind-limb muscle. Desmin, muscle creatine kinase and troponin C mRNAs were used as markers for myoblast determination, myotubule formation and myofibre maturation, respectively. The mRNA quantities were determined by competitive reverse transcriptase-polymerase chain reaction. The expression profile of desmin mRNA indicated that myoblast determination occurred before E11 in both the tongue and hind-limb muscles; the profile of muscle creatine kinase and troponin C mRNAs indicated that myotubule formation and myofibre maturation began between E11 and 13 in both tongue and hind-limb muscles, but ended 2 days earlier in the tongue than in the hind limb. Expression of myoD and myogenin mRNAs began at E11, increased, and showed peak values earlier in the tongue muscle (E13) than in the hind-limb muscle (E15). Expression of MRF4 mRNA appeared earlier in the tongue (E13) than in the hind-limb muscle (E15) and increased in both muscles after that. These results suggest that myotubule formation and myofibre maturation in the tongue muscle progress faster than in the hind-limb muscle, a result of earlier expression of myoD, myogenin, and MRF4 in response to earlier functional demands such as suckling immediately after birth.

Lack of a strong association of CTLA-4 exon 1 polymorphism with the susceptibility to rheumatoid arthritis and systemic lupus erythematosus in Japanese: an association study using a novel variation screening method

CTLA-4 is considered to be one of the attractive candidates for the susceptibility genes to rheumatic diseases. In the present study, the association of CTLA-4 polymorphism with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) was examined in the Japanese population using the case-control association analysis. Polymerase chain reaction-preferential homoduplex formation assay (PCR-PHFA) was applied for the screening of genetic variations and for the genotyping of a large number of samples. A greater proportion of Japanese patients with RA (44%) and SLE (44%) compared with healthy individuals (37%) had exon 1 49 G/G genotype, but the difference did not reach statistical significance. However, when the patients with RA and healthy individuals were stratified according to HLA-DRB1 alleles, a weakly significant increase of the positivity of CTLA-4 49G allele was observed in HLA-DRB1*0405-positive patients (87%) compared with DRB1*0405-positive healthy individuals (71%) (P = 0.014, odds ratio = 2.77). These results indicate that CTLA-4 exon 1 polymorphism does not contribute greatly to the susceptibility to RA and SLE, at least in Japanese, although the presence of CTLA4 49G allele could be a minor predisposing factor for RA in HLA-DRB1*0405-positive individuals. In addition, PCR-PHFA was shown to be useful for a mass screening of gene variations.

Nerve growth factor (NGF) supports tooth morphogenesis in mouse first branchial arch explants

Posterior midbrain and anterior hindbrain neuroectoderm trans-differentiate into cranial neural crest cells (CNCC), emigrate from the neural folds, and become crest-derived ectomesenchyme within the mandibular and maxillary processes. To investigate the growth factor requirement specific for the initiation of tooth morphogenesis, we designed studies to test whether nerve growth factor (NGF) can support odontogenesis in a first branchial arch (FBA) explant culture system. FBA explants containing neural-fold tissues before CNCC emigration and the anlagen of the FBA were microdissected from embryonic day 8 (E8) mouse embryos, and cultured for 8 days in medium supplemented with 10% fetal calf serum only, or serum-containing medium further supplemented with either NGF or epidermal growth factor (EGF) at three different concentrations: 50, 100, or 200 ng/ml. Morphological, morphometric, and total protein analyses indicated that growth and development in all groups were comparable. Meckel's cartilage and tongue formation were also observed in all groups. However, odontogenesis was only detected in explants cultured in the presence of exogenous NGF. NGF-supplemented cultures were permissive for bud stage (50 ng/ml) as well as cap stage of tooth morphogenesis (100 and 200 ng/ml). Morphometric analyses of the volume of tooth organs showed a significant dose-dependent increase in tooth volume as the concentration of NGF increased. Whole-mount in situ hybridization and semiquantitative reverse transcription-polymerase chain reaction for Pax9, a molecular marker of dental mesenchyme, further supported and confirmed the morphological data of the specificity and dose dependency of NGF on odontogenesis. We conclude that (1) E8 FBA explants contain premigratory CNCC that are capable of emigration, proliferation, and differentiation in vitro; (2) serum-supplemented medium is permissive for CNCC differentiation into tongue myoblasts and chondrocytes in FBA explants; and (3) NGF controls CNCC cell fate specification and differentiation into tooth organs.