Morphological studies of the epiphyseal growth zone in the brachymorphic (bm/bm) mouse

Light microscopy, including immunohistochemical techniques, and electron microscopy were performed on epiphyseal growth cartilage from brachymorphic (bm/bm) mice and age-matched phenotypically normal siblings aged 5, 16 and 25 days. In the bm/bm mice light microscopy showed a disturbed columnar arrangement and numerous chondrocytes with pronounced regressive changes. The normal development of proliferative cells into hypertrophic cells was halted and thus only a rather small and ill-defined hypertrophic zone was seen. The calcifying zone was irregular and the normal lacunae were replaced by a densely staining matrix. Using immunofluorescence techniques, the presence of considerable amounts of both type II and type V collagen was demonstrated in the bm/bm mice, while the cartilage from controls contained only type II. Ultrastructurally the lacunar matrix contained bundles of fine fibrils without the typical collagen periodicity which might indicate synthesis of a defective procollagen. Our observations together with the previously demonstrated deficiency of 3'-phosphoadenosine 5'-phosphosulphate, illustrate the complexity of the growth cartilage disturbance in the bm/bm mouse. Most of our findings are at variance with those described in the literature and possible pathogenetic mechanisms for the observed alterations in the growth cartilage are discussed.     

Brachymorphic mice (bm/bm): A generalized biochemical defect expressed primarily in cartilage

Homozygous brachymorphic (bm/bm) mice have a disproportionately short stature. Previous studies have shown that the cartilage proteoglycan is undersulfated as a result of decreased 3′-phosphoadenosine 5′-phosphosulfate (PAPS) levels. In the studies reported here, PAPS synthesizing activity was found to be decreased in both skin fibroblasts and prechondrogenic mesenchyme, but sulfation of glycosaminoglycan was normal in those tissues unless glycosaminoglycan synthesis was enhanced by β-d-xyloside. Furthermore, undersulfation was correlated with increased proteoglycan synthesis as the limb mesenchyme cultures underwent chondrogenesis, and sulfation proceeded in an “all or none” manner. These observations demonstrate that the molecular defect in bm/bm mice is not restricted to cartilage, but is manifested there because of the large amount of chondroitin sulfate synthesized.     

The histochemistry of complex carbohydrates in certain organs of homozygous brachymorphic (bm/bm) mice

Summary Homozygous brachymorphic (bm/bm) mice are characterized by disproportionately short stature and by undersulphated proteochondroitin sulphate in cartilage with a defect in the synthesis of the sulphate donor (3-phosphoadenosine-5-phosphosulphate: PAPS). In adult mice of this mutant strain, several organs have been examined by light microscopical methods of complex carbohydrate histochemistry, in comparison with those from control (C57BL/6J) mice of comparable ages. The organs included the trachea, aorta, skin, stomach colon and cornea. In the nutant mice, connective tissue elements and components of epithelial tissues exhibited apparently weaker positive reactions for ester sulphate groupings of complex carbohydrates, as compared with those in the control mice. From these results, it is concluded that the undersulphation in complex carbohydrates is widespread throughout the connective and epithelial tissues of the mutant mice.     

Localization of anionic constituents in mast cell granules of brachymorphic (bm/bm) mice by using avidin-conjugated colloidal gold

We used the egg avidin gold complex as a polycationic probe for the localization of negatively charged sites in the secretory granules of mouse mast cells. We compared the binding of this reagent to mast cell granules in wild-type mice and in congenic brachymorphic mice in which mast cell secretory granules contained undersulfated proteoglycans. We localized anionic sites by post-embedding labeling of thin sections of mouse skin and tongue tissues fixed in Karnovsky’s fixative and OsO₄ and embedded in Araldite. Transmission electron microscopy revealed that the mast cell granules of bm/bm mice had a lower optical density than those of wild-type mice (P<0.001) and a lower avidin gold binding density (by approximately 50%, P<0.001). The latter result provided additional evidence that the contents of mast cell granules in bm/bm mice were less highly sulfated than in those of wild-type mice. In both wild-type and bm/bm mast cells, the distribution of granule equivalent volumes was multimodal, but the unit granule volume was approximately 19% lower in bm/bm cells than in wild-type cells (P<0.05). Thus, bm/bm mast cells develop secretory granules that differ from those of wild-type mice in exhibiting a lower optical density and slightly smaller unit granules, however the processes that contribute to granule maturation and granule-granule fusion in mast cells are operative in bm/bm cells.     

Studies of twoH-2D b mutants: B6.C-H-2 bm13 and B6.C-H-2 bm14

Two new C57BL/6H-2 mutants,B6.C-H- 2^bm13 and B6.C-H- 2^bm14 are described. They arose independently in C57BL/6 as spontaneous mutations of the gain and loss type. Complementation studies map the mutations in both bm13 and bm14 to theH-2D ^b gene. How ever, these two mutant strains are not identical, but occurred as independent mutations at the same locus, as shown by reciprocal graft rejection and by the inability of the (bm13 × bm114)F₁ hybrid to accept C57BL/6 grafts. Serological studies by direct testing (cytotoxicity and hemagglutination) and by quantitative absorption demonstrated a decrease in the H-2D^b private specificity H-2.2 in both bm13 and bm14 when compared to C57BL/6. This was confirmed by SDS-PAGE analysis using antisera detecting the H-2.2 specificity. Attempts to produce antibodies to either the gained or lost specificities of the two mutant strains failed.     

Studies of two H-2Db mutants: B6. C-H-2bm13 and B6.C-H-2bm14

Two new C57BL/6 H-2 mutants, B6.C-H-2bm13 and B6.C-H-2bm14 are described. They arose independently in C57BL/6 as spontaneous mutations of the gain and loss type. Complementation studies map the mutations in both bm13 and bm14 to the H-2Db gene. However, these two mutant strains are not identical, but occurred as independent mutations at the same locus, as shown by reciprocal graft rejection and by the inability of the (bm13 X bm14)F1 hybrid to accept C57BL/6 grafts. Serological studies by direct testing (cytotoxicity and hemagglutination) and by quantitative absorption demonstrated a decrease in the H-2Db private specificity H-2.2 in both bm13 and bm14 when compared to C57BL/6. This was confirmed by SDS-PAGE analysis using antisera detecting the H-2.2 specificity. Attempts to produce antibodies to either the gained or lost specificities of the two mutant strains failed.     

Cross-reactive recognition of mouse cells expressing the bm3 and bm11 mutations within H-2Kb by H-2Kb-restricted herpes simplex virus-specific cytotoxic T lymphocytes

Cytotoxic T lymphocytes, generated in C57BL/6 mice in response to herpes simplex virus type 1 (HSV) and known to be restricted in their recognition of HSV-encoded antigen(s) in association with the class I H-2Kb gene product, were consistently found to contain a subpopulation that recognized and lysed uninfected, SV40-transformed cells that expressed the H-2Kbm3 and H-2Kbm11 mutant class I gene products on their cell surface. The mutant cell lines, designated Lgbm3SV and Kbm11SV, share a common amino acid substitution at position 77, with the bm3 mutation having an additional amino acid substitution at position 89. Cross-reactive lysis was observed only after in vivo priming with HSV, suggesting an important role for an antigen-dependent driving step in the expansion of these cross-reactive CTL. The phenotype of the cross-reactive effector population was further confirmed as a T lymphocyte by negative-selection techniques. Limiting dilution analysis of the frequency of cross-reactive CTL precursors suggested that cross-reactivity was mediated by a subpopulation of HSV-specific CTL, and this was confirmed by clonal analysis of the reactivity patterns of short-term, HSV-specific CTL clones. However, analysis of the specificity of the cross-reactive CTL population by cold-target inhibition of bulk culture-derived CTL, or by Spearman ranking analysis of limiting dilution-derived CTL, indicated that the specificity of the cross-reactive population for HSV-infected H-2b target cells and for uninfected bm3 or bm11 target cells was quite distinct. These findings suggested that the cross-reactive CTL population played little, if any, role in the HSV-specific CTL response as measured in vitro. The findings also suggested that the HSV-specific CTL clones able to mediate cross-reactive recognition of the bm3 and bm11 targets had a higher intrinsic avidity for the foreign target than for the inducing antigen.     

Polymorphism of the bm86 Gene in South American Strains of the Cattle Tick Boophilus microplus

Thirty Boophilus microplus strains from various geographic regions of Brazil, Argentina, Uruguay, Venezuela and Colombia were analyzed for the bm86 and bm95 gene. A fragment of cDNA of 794 base pairs of the parasite larvae, included between nucleotides 278–1071s, was amplified and cloned on the pGEM-T vector. Two random clones were sequenced for each population and the nucleotides 278–1071 and predicted amino acid sequences compared with the bm86 and bm95 genes. Variations from 1.76 to 3.65% were detected in the nucleotides sequence when compared with the homologous sequence of the bm86 gene and a 3.4–6.08% in the homologous amino acid sequence of the Bm86 protein. When the sequences obtained were compared with the bm95 gene, variations from 0.50 to 3.15% were detected. Variations from 1.14 to 4.56% were detected for the Bm95 protein homologous sequences in the deduced amino acid sequence. Only five of the 30 strains analyzed presented two different types of alleles expressed and the two alleles of the Alegre population and allele 1 of the Betim population were the most divergent of all those analyzed.     

Biochemical studies of H-2K antigens from a group of related mutants. II. Identification of a shared mutation in B6-H-2 bm6 , B6.C-H-2 bm7 , and B6.C-H-2 bm9

In an earlier paper, we presented evidence that two independent mutants of the bg series, B6-H-2 ^bm5 (bm5) and B6-H-2 ^bm16 (bm16) carry identical mutations such that tyrosine at residue number 116 of the H-2K^b molecule from the parent strain C57BL/6Kh is replaced by a phenylalanine in each of the two mutant molecules. In this paper, we demonstrate, using similar techniques, that the independent bg series mutants B6-H-2 ^bm6 (bm6), B6.C-H-2 ^bm7 (bm7), and B6.C-H-2 ^bm9 (bm9), which share biological properties with bm5 and bm16, can be grouped together because they share two identical mutations, one of which is common to bm5 and bm16, a Tyr to Phe interchange at residue number 116. In addition, a second mutation is at residue number 121, where a Cys in the H-2K molecule from 136 is substituted with an Arg in the mutant. Since all of the bg series mutants arose independently and share biological and biochemical characteristics, it is anticipated that study of these mutants could lead to some understanding of the high mutation rate in the K^b molecule.     

Biochemical studies on the H-2K mutant B6.C-H-2 bm10

The H-2K glycoprotein from the MHC mutant bm10 was analyzed biochemically to determine where primary structural differences distinguished it from the parental standard molecule, K^b. Comparative peptide maps showed differences in two peptides known to be part of the parental CNBr fragment spanning amino acids 139 to 228. Partial sequence analyses of CNBr fragments and tryptic peptides identified two tightly clustered amino acid substitutions at amino acids 165 (Val to Met) and 173 (Lys to unknown). The substitutions in bm10 represent the most carboxy-terminal substitutions characterized in the K^b molecules of the spontaneous, histogenically active H-2 mutants.     

Immunogold labelling of arabinoxylans in the plant cell walls of normal and bm3 mutant maize

Summary— Polyclonal antibodies directed against α, l -1.2-arabinofuranosyl poly-β,d -1.4-xylopyranosyl (degree of polymerization 130) have been raised from rabbits. The immunogold labelling in transmission electron microscopy (TEM) evidenced the arabinoxylans of the plant cell walls. Comparison between the stems of normal and mutant bm3 maize demonstrated a greater accessibility of arabinoxylans in the walls of the mutant maize. The method, specific and swift, allows us to specify the repartition in the different parts of the stem: sclerenchyma, fibers, parenchyma.     

Molecular markers near the mouse brachymorphic (bm) gene,which affects connective tissues and bleeding time

Several inherited skeletal/connective tissue defects are associated with hemorrhagic disorders in humans. Accordingly, three mouse mutants (brachymorphic [bm], hemimelic extra toes [Hx], and ulnaless [Ul]), with inherited skeletal abnormalities, were analyzed for hemorrhagic tendencies. All three had prolonged bleeding times. Platelet numbers, size, and function, as well as common soluble plasma clotting factors, were not measurably affected. To further define the bm mutation, its chromosomal location relative to 19 other molecular markers was determined to a high resolution in a large interspecific backcross. Several microsatellite markers were found to be very closely linked to bm and should provide useful entry points for the eventual identification of this gene by positional/candidate cloning techniques. These results suggest that inherited skeletal abnormalities and bleeding tendencies are associated more frequently in both humans and animal models than is commonly recognized. Identification of these genes may reveal novel relationships between osteogenesis and hemostasis. Received: 14 August 1995 / Accepted: 19 September 1995     

The maize brown midrib4 (bm4) gene encodes a functional folylpolyglutamate synthase

Mutations in the brown midrib4 (bm4) gene affect the accumulation and composition of lignin in maize. Fine‐mapping analysis of bm4 narrowed the candidate region to an approximately 105 kb interval on chromosome 9 containing six genes. Only one of these six genes, GRMZM2G393334, showed decreased expression in mutants. At least four of 10 Mu‐induced bm4 mutant alleles contain a Mu insertion in the GRMZM2G393334 gene. Based on these results, we concluded that GRMZM2G393334 is the bm4 gene. GRMZM2G393334 encodes a putative folylpolyglutamate synthase (FPGS), which functions in one‐carbon (C1) metabolism to polyglutamylate substrates of folate‐dependent enzymes. Yeast complementation experiments demonstrated that expression of the maize bm4 gene in FPGS‐deficient met7 yeast is able to rescue the yeast mutant phenotype, thus demonstrating that bm4 encodes a functional FPGS. Consistent with earlier studies, bm4 mutants exhibit a modest decrease in lignin concentration and an overall increase in the S:G lignin ratio relative to wild‐type. Orthologs of bm4 include at least one paralogous gene in maize and various homologs in other grasses and dicots. Discovery of the gene underlying the bm4 maize phenotype illustrates a role for FPGS in lignin biosynthesis.     

Brown‐midrib maize (bm1) – a mutation affecting the cinnamyl alcohol dehydrogenase gene

Brown-midrib (bm) mutants of maize have modified lignin of reddish-brown colour. Although four independent bm loci are known, only one of the mutant genes has been previously identified. We report here that maize bm1, one of the less characterised mutants, shows severely reduced CAD activity in lignified tissues, resulting in the production of a modified lignin. Both the total lignin content and the structure of the polymer are altered by the mutation. We further describe the isolation and characterisation of the maize CAD cDNA and mapping of the CAD gene. CAD maps very closely to the known location of bm1 and co-segregates with the bm1 locus in two independent recombinant inbred populations. These data strongly support the premise that maize bm1 directly affects expression of the CAD gene.     

Idiotypic and fluorometric analysis of the antibodies that distinguish the lesion of the I-A mutant B6.C-H-2bm12

The serologic lesion of the I-A mutant mouse strain, bm12, was investigated with the use of monoclonal anti-Iab antibodies and anti-idiotypic (Id) reagents produced against these antibodies. In a fluorometric analysis, three different monoclonal anti-Iab antibodies (25-9-17, 34-5-3, 28-16-8) failed to bind bm12 cells, whereas two anti-Iab antibodies (25-5-16 and 17/227), which bound bm12 cells, showed about one-half the fluorescence intensity that they showed in binding to Iab antigens. Of the three monoclonal antibodies that failed to react with bm12 cells, two antibodies (25-9-17 and 34-5-3) were found to bind the same steric site on Iab molecules (cluster I). In contrast, the antibodies (25-5-16 and 17/227) that reacted with both Iab and Iabm12 antigens were found to bind a second distinct site (cluster II). The binding of antibody 28-16-8 to Iab antigens inhibited reciprocally the binding of cluster I and II anti-Iab antibodies, suggesting a possible third site, sterically located intermediate between the other two sites. To assess the relatedness of the antibodies defining the serologic lesion of bm12 mice, xenogeneic and syngeneic anti-Id reagents were produced against antibodies 25-9-17 and 28-16-8. By using these anti-Ids in a binding site-related inhibition assay, a cross-reactive idiotype was detected that is shared by 25-9-17 and 34-5-3 antibodies; thus these two monoclonal antibodies share several features, including 1) idiotypic determinants, 2) failure to bind bm12 cells, 3) binding the same spatial Iab site, and 4) having indistinguishable serologic fine specificity that corresponds with a previously defined predominant alloantigenic determinant recognized in the bm12 anti-Iab humoral response. Therefore, several parameters of antibody recognition of Ia can now be correlated with structural changes in Ia molecules. These findings will potentiate future studies of the T cell recognition of these same Ia epitopes.     

Biochemical studies of H-2K antigens from a group of related mutants. I. Identification of a shared mutation in B6-H-2 bm5 and B6-H-2 bm16

Structural studies of the H-2 gene products from a group of five closely related but independent C57BL/6 H-2 mutant mice were undertaken. Each of the mutants exhibits reciprocal graft rejection with the parent. The group is remarkable, however, because each member of this group can accept skin grafts from any other member. The results of biochemical analysis of the H-2 glycoproteins from two of these related mutants, bm5 and bm16, are presented in this report. Evidence is given that the H-2K molecules from these two mutants are identical to each other based on comparative tryptic peptide mapping profiles with the parent. From partial amino acid sequence analysis, K products of both mutants have at least one common difference from the parental type located at residue number 116. Definitive studies established that in both bm5 and bm16 a tryosine found in the parent molecule is substituted with a phenylalanine in the mutant. These results show that a biochemical difference between the K products of the two mutants and of the parent can be detected, that the mutants appear to be identical with one another even though they arose independently, and that they differ from the other H-2K ^b mutants analyzed.Abbreviations used in this paper B6 C57BL/6Kh - bm5 B6-H-2^bm5 - bm6 B6-H-2 ^bm6 - bm7 B6.C-H-2 ^bm7 - bm9 B6.C-H-2 ^bm9 - bm16 B6-H-2 ^bm16 - D H-2D - K H-2K - MHC major histocompatibility complex