Increased expression of the gene for the pro alpha 1(IV) chain of basement-membrane procollagen in cultured skin fibroblasts from two variants of osteogenesis imperfecta.

Fibroblasts from two lethal variants of osteogenesis imperfecta were shown to synthesize increased amounts of type IV procollagen. Previous studies established that one of these variants had a non-functional allele for the pro alpha 2 chain of type I procollagen, whereas the other pro alpha 2(I) allele contained a mutation leading to synthesis of shortened pro alpha 2(I) chains. In the two variants, the relative level of mRNA for pro alpha 1(IV) was 31 and 42% of the level of mRNA for pro alpha 1(I) chains. A value of less than 2% was found for a third lethal and four non-lethal variants of osteogenesis imperfecta. Immunofluorescent staining of fibroblasts from the two variants synthesizing increased amounts of type IV procollagen indicated that a homogeneous population of cells synthesized both type IV and type I procollagen. The results suggest that mutations in the type I procollagen genes that result in osteogenesis imperfecta can be associated with increased expression of the genes for type IV procollagen.     

Factors affecting the activity patterns of black-backed jackals Canis mesomelas

Daily activity levels of black-backed jackals Canis mesomelus were determined in southern Africa through direct observation and radio-tracking. Jackals have a bigeminus activity pattern that is closely paralleled by the activity levels of some of their most important prey. Although differences due to sex, age, study area and season of year were found, this activity pattern was most markedly influenced by light conditions during both the crepuscular and the nocturnal periods.     

Synthesis of a shortened pro-alpha 2(I) chain and decreased synthesis of pro-alpha 2(I) chains in a proband with osteogenesis imperfecta

Synthesis of type I procollagen was examined in skin fibroblasts from a proband with a lethal variant of osteogenesis imperfecta. The fibroblasts synthesized shortened pro-alpha 2(I) chains and these shortened chains accounted for all the pro-alpha 2(I) chains synthesized by the cells. In addition, there was a decrease in the relative rate of synthesis of pro-alpha 2(I) chains. Fragmentation of the shortened pro-alpha 2(I) chains with vertebrate collagenase and cyanogen bromide demonstrated that the shortening was in alpha 2(I)-CB3,5A, a fragment from about the middle of the chain containing amino acid residues 361 to 775. Based on the relative mobility in electrophoretic gels, the shortening was about 20 amino acid residues. The decreased synthesis of pro-alpha 2(I) chains was demonstrated by an increase in the ratio for the rates of synthesis of pro-alpha 1(I):pro-alpha 2(I) chains. It was associated with an increase in the ratio of mRNAs for pro-alpha 1(I):pro-alpha 2(I) in the cells. Fibroblasts from the father also demonstrated a decreased synthesis of pro-alpha 2(I) chains as reflected by an increase in the ratio of newly synthesized pro-alpha 1(I):pro-alpha 2(I) chains. No shortened pro-alpha 2(I) chains were seen in fibroblasts from either the father or the mother. The observations suggested that the proband inherited a nonfunctioning pro-alpha 2(I) gene from her father and that the gene for the shortened pro-alpha 2(I) chain probably arose from a sporadic mutation.     

Tripsacum-maize interaction: a novel cytogenetic system

The genera Zea and Tripsacum cross readily when they are not isolated by gametophytic barriers, and it has been postulated that intergeneric introgression played a role in the evolution of maize. The basic x = 9 Tripsacum and x = 10 Zea genomes have little cytological affinity for each other in hybrids that combine 10 Zea with 18 Tripsacum chromosomes. However, one to four Tripsacum chromosomes sometimes associate with Zea chromosomes in hybrids between Z. mays (2n = 20) and T. dactyloides (2n = 72). These hybrids with 10 Zea and 36 Tripsacum chromosomes frequently produce functional female gametes with 36 Tripsacum chromosomes only. When they are pollinated with maize, their offspring again have 36 Tripsacum and 10 maize chromosomes, but the Tripsacum genome is contaminated with maize genetic material. In these individuals, intergenome pairing is the rule, and when they are pollinated with maize, their offspring have 36 Tripsacum and 10, 12, 14, 16, 18, or 20 Zea chromosomes. Plants with 36 Tripsacum and 20 Zea chromosomes behave cytologically as alloploids, although the Tripsacum genome is contimated with maize, and one basic maize genome is contaminated with with Tripsacum genetic material. When they are pollinated with maize, offspring with 18 Tripsacum and 20 Zea chromosome are obtained. Further successive backcrosses with maize selectively eliminate Tripsacum chromosomes, and eventually plants with 2n = 20 Zea chromosomes are recovered. Many of these maize plants are highly "tripsacoid." Strong gametophytic selection for essentially pure Zea gametes, however, eliminates all obvious traces of Tripsacum morphology within a relatively few generations.     

Decreased thermal denaturation temperature of osteogenesis imperfecta mutant collagen is independent of post-translational overmodifications of lysine and hydroxylysine

Fibroblasts from many patients with osteogenesis imperfecta (OI) synthesize and secrete Type I collagen which is both overmodified and exhibits a decreased thermal denaturation temperature. We have examined the relationship between overmodification and decreased melting temperature in several favorable OI mutants by selectively inhibiting lysyl hydroxylase activity with the drug Minoxidil and comparing the melting profiles of the resultant undermodified collagen with untreated control. Minoxidil treatment causes an appreciable decrease in hydroxylysine with compensatory increases in lysine content, and the delayed sodium dodecyl sulfate-polyacrylamide gel electrophoretic mobility of the overmodified collagen chains becomes normal. However, the decreased melting temperature was unchanged from untreated OI control. When unhydroxylated collagen produced by normal control and OI fibroblasts incubated with alpha,alpha'-dipyridyl was examined, mutant OI molecules melted at a lower temperature than control. These data indicate that the decreased thermal denaturation temperature of OI mutant collagen is independent of post-translational overmodification of lysine or hydroxylysine. Presumably, substitutions for glycine in the Gly-X-Y structural motif distort the helix and produce lower melting temperatures by presently unknown mechanisms.     

Fatty acid composition as a taxonomic characteristic for Microcystis and other coccoid cyanobacteria (blue-green alga) isolates

The taxonomic importance of fatty acid composition at genus and sub-genus level was evaluated by analysing the fatty acid composition of fourteen different Microcystis isolates and seven additional members of the order Chroococcales. Fatty acid composition proved to be consistent within isolates. Isolates were clustered into two major groups, namely A and B. Group B contained all the Microcystis isolates and was further divided into subgroups of varying similarity indicating the existence of different taxa. The Microcystis isolates were characterised by a high content of polyunsaturated fatty acids (27–44%) and a low content of palmitoleate. The test organisms were arranged in a scheme indicating their possible phylogenetic relationship based on fatty acid composition and other phenotypic characteristics. According to our data the toxic strains, represented by different isolates, of Microcystis appear as a distinct group. Furthermore two dubious species namely Microcystis incerta and a Synechocystis sp. could clearly be reasigned to different genera. The results demonstrated that fatty acid composition is an effective taxonomic tool in clarifying taxonomical problems of Microcystis isolates. Department of Microbiology, University of the Orange Free State