Effects ofPax3Modifier Genes on Craniofacial Morphology, Pigmentation, and Viability: A Murine Model of Waardenburg Syndrome Variation

Waardenburg syndrome type 1 is caused by mutations inPAX3.Over 50 humanPAX3mutations that lead to hearing, craniofacial, limb, and pigmentation anomalies have been identified. APAX3mutant allele, segregating in a family, can show reduced penetrance and variable expressivity that cannot be explained by the nature of the mutation alone. TheMus musculus Pax3mutationSp^d(Splotch-delayed, Pax3[formula]), coisogenic on the C57BL/6J (B₆) genetic background, produces in heterozygotes a white belly spot with 100% penetrance and very few other anomalies. By contrast, manySp^d/+ BC₁progeny [F₁♀Sp^d/+ (♀Sp^d/+ B₆× ♂ +/+Mus spretus) × ♂ +/+ B₆] exhibit highly variable craniofacial and pigmentary anomalies. Of the BC₁Sp^d/+ progeny, 23.9% are estimated to be nonviable, and 32.1% are nonpenetrant for the white belly spot. The penetrance and expressivity of theSp^d/+ genotype are controlled in part by the genetic background and the sex of the individual. A minimum of two genes interact withSp^dto influence the craniofacial features of these mice. One of these genes may be either X-linked or sex-influenced, while the other is autosomal. TheA-locus (Agouti) or a gene closely linked toAalso plays a role in determining craniofacial features. At least one additional gene, possibly theA-locus or a gene linked toA,interacts withSp^dand determines the presence and size of the white belly spot. The viability of BC₁mice is influenced by at least three factors:Sp^d,A-locus alleles or a gene closely linked to theA-locus, and the sex of the mouse. These BC₁mice provide an opportunity to identify genes that interact with and modify the expression ofPax3and serve as a model to identify the genes that modify the expression of humanPAX3mutations.     

Past vegetation changes in the Brazilian Pantanal arboreal–grassy savanna ecotone by using carbon isotopes in the soil organic matter

Measurements of the organic carbon inventory, its stable isotopic composition and radiocarbon content were used to deduce vegetation history from two soil profiles in arboreal and grassy savanna ecotones in the Brazilian Pantanal. The Pantanal is a large floodplain area with grass-dominated lowlands subject to seasonal flooding, and arboreal savanna uplands which are only rarely flooded. Organic carbon inventories were lower in the grassy savanna site than in the upland arboreal savanna site, with carbon decreasing exponentially with depth from the surface in both profiles. Changes in ¹³C of soil organic matter (SOM) with depth differed markedly between the two sites. Differences in surface SOM ¹³C values reflect the change from C₃ to C₄ plants between the sites, as confirmed by measurements of ¹³C of vegetation and the soil surface along a transect between the upland closed-canopy forest and lowland grassy savanna. Changes of ¹³C in SOM with depth at both sites are larger than the 3–4 per mil increases expected from fractionation associated with organic matter decomposition. We interpret these as recording past changes in the relative abundance of C₃ and C₄ plants at these sites. Mass balances with ¹⁴C and ¹³C suggest that past vegetational changes from C₃ to C₄ plants in the grassy savanna, and in the deeper part of the arboreal savanna, occurred between 4600 and 11 400 BP, when major climatic changes were also observed in several places of the South American Continent. The change from C₄ to C₃, observed only in the upper part of the arboreal savanna, was much more recent (1400 BP), and was probably caused by a local change in the flooding regime.     

Aberrant Transpositions of Maize Double Ds-Like Elements Usually Involve Ds Ends on Sister Chromatids

McClintock's analysis of chromosome-breaking Dissociation (Ds) elements in maize demonstrated that sister chromatids fuse at the position of Ds, forming a dicentric chromosome and an acentric fragment. In tobacco, Ds left and right ends in direct orientation (that is, half a double Ds) are sufficient to promote Activator-dependent marker gene loss. We present here a detailed analysis of germinally inherited rearrangements promoted by "half double Ds" elements and a characterization of rearrangements that involve inversion of the segment between the Ds ends and/or deletion of a segment adjacent to the Ds construct. The results support a model in which chromosome breakage promoted by these elements, and presumably by double Ds elements, involves Ds ends on sister chromatids.     

HYDROBIIDAE (GASTROPODA: HYDROBIOIDEA) FROM THE RIBEIRA VALLEY, S.E. BRAZIL, WITH DESCRIPTIONS OF TWO NEW CAVERNICOLOUS SPECIES

Potamolithus karsticus n. sp. and Potamolithus troglo-bius n.sp., two Brazilian aquatic cavesnails (Gastropoda: Hydrobiidae),are described. P. troglobius is blind and depigmented, and isthe first stygobiontic snail to be described from Brazil Additionally, specimens of Potamolithus ribeirensis Pilsbry,1911 were collected near the type locality for comparison withthe new cave species (Received 2 December 1993; accepted 20 June 1994)     

Direct observation of the iron binding sites in a ferritin

X-Ray analysis of the ferritin of Escherichia coli (Ec-FTN) and of Ec-FTN crystals soaked in (NH₄)₂Fe(SO₄)₂ has revealed the presence of three iron-binding sites per subunit. Two of these form a di-iron site in the centre of the subunit as has been proposed for the ‘ferroxidase centres’ of human ferritin H chains. This di-iron site, lying within the 4-alpha-helix bundle, resemble those of ribonucleotide reductase, methane monoxygenase and haemerythrin. The third iron is bound by ligands unique to Ec-FTN on the inner surface of the protein shell. It is speculated that this state may represent the nucleation centre of a novel type of Fe(III) cluster, recently observed in Ec-FTN.     

The circumorbital foramina in primates

This paper documents the diversity and variation in the circumorbital foramina in extant primates. A qualitative and quantitative analysis of the circumorbital foramina, comprising the supraorbital foramen, the infraorbital foramen, and the malar foramen, was carried out using representative species from nine extant families of primates. The information obtained from the study is used to reconstruct ancestral morphotypes, and to make inferences about evolutionary changes that may have taken place in the major primate lineages. In addition, the analysis provides useful comparative data for interpretation of the phylogenetic significance and paleobiological implications of the circumorbital foramina in fossil primates.     

Chloroplast targeting of spectinomycin adenyltransferase provides a cell-autonomous marker for monitoring transposon excision in tomato and tobacco

Antibiotic resistance genes can act as either cell autonomous or non-cell autonomous genetic markers with which to monitor the excision of plant transposons. To convert spectinomycin resistance from a noncell autonomous resistance to cell autonomous resistance, a transit peptide for chloroplast localization from a petunia ribulose bisphosphate carboxylase (rbcS) gene was fused in-frame to the aadA gene, which confers spectinomycin and streptomycin resistance. Constructs were generated in which the expression of this chimeric gene was prevented by the presence, in the 5 untranslated leader, of the maize transposons Activator (Ac) or Dissociation (Ds). When progeny of tobacco or tomato plants transformed with these constructs were germinated on spectinomycin-containing medium, germinally revertant and somatically variegated individuals could be distinguished.     

Phylogenetic relationships of the garter snakes based on DNA sequence and allozyme variation

We estimated phylogenetic relationships among 26 species of garter snakes (genus Thamnophis ) using allozyme and mitochondrial cytochrome b gene nucleotide sequence variation. Parsimony analyses of the two data sets give substantially different estimates of phylogeny. Several lines of evidence indicate that much of this conflict is due to error associated with the restricted number of characters in each data set. Such sampling error may be reduced by combining all the characters; we therefore present an estimate of phylogeny based on parsimony analysis of all the data combined. All our analyses support several conclusions in conflict with previous views: a very distant relationship between T.errans and T. elegans , non-monophyly of the elegans group (even excluding T: errans ), and nesting of the form validus (previously considered a member of the genus Nerodia ) within Thamnophis.
The combined analysis gives an almost fully resolved tree. However, bootstrapping indicates only weak support for many clades in this tree. Furthermore, paraphyly of the assemblages of cytochrome b gene lineages within T. elegans and T. radix indicate the potential for discordance between the mitochondrial DNA (mtDNA) and species phylogenies through the sorting of ancestral mtDNA polymorphisms. These problems suggest the need for assaying additional characters, especially ones likely to be independent of those used in the present study.