How rapidly does the human mitochondrial genome evolve?

The results of an empirical nucleotide-sequencing approach indicate that the evolution of the human mitochondrial noncoding D-loop is both more rapid and more complex than is revealed by standard phylogenetic approaches. The nucleotide sequence of the D-loop region of the mitochondrial genome was determined for 45 members of a large matrilineal Leber hereditary optic neuropathy pedigree. Two germ-line mutations have arisen in members of one branch of the family, thereby leading to triplasmic descendants with three mitochondrial genotypes. Segregation toward the homoplasmic state can occur within a single generation in some of these descendants, a result that suggests rapid fixation of mitochondrial mutations as a result of developmental bottlenecking. However, slow segregation was observed in other offspring, and therefore no single or simple pattern of segregation can be generalized from the available data. Evidence for rare mtDNA recombination within the D-loop was obtained for one family member. In addition to these germ-line mutations, a somatic mutation was found in the D-loop of one family member. When this genealogical approach was applied to the nucleotide sequences of mitochondrial coding regions, the results again indicated a very rapid rate of evolution.     

Enhanced system kLa and permeate flux with a ceramic membrane bioreactor

Summary A cross-flow ceramic membrane was coupled to a bioreactor to fulfil the alternate functions of process stream clarifier and primary aerator. At the same air supply rate (delivered as a back-flush), ceramic membranes provided up to 72% greater aeration than a ring-sparger located in the bioreactor. In Biol.ogical treatment of dairy food process waste, the air backflush had the additional benefit of inhibiting membrane fouling, thereby maintaining higher (by about 100%) permeate fluxes.     

Preserving racial hierarchy amidst changing racial demographics: how neighbourhood racial preferences are changing while maintaining segregation

Despite long-term, documented declines in racialized attitudes, racial inequality persists. Scholars have theorized why this dissonance exists but few have empirically demonstrated how views can become more progressive while simultaneously maintaining inequality. The present study uses neighbourhood racial preferences and their influence on racial residential segregation to demonstrate how in a diversifying context residents can become more “accepting” while simultaneously maintaining the racial hierarchy, the opposite of what most of the literature currently assumes. Using data from three distinct sources in the United States, this research finds that U.S. residents are increasingly willing to live amidst diversity yet whites still concentrate in white neighbourhoods. In short, white Americans are more willing to live in diverse neighbourhoods than in the past, but they are not willing to desegregate. We argue this preserves racial inequality. We conclude with a discussion of our findings and their implications for future research and practice.     

Mouse disabled (mDab1): a Src binding protein implicated in neuronal development.

Here, we identify a mouse homolog of the Drosophila Disabled (Dab) protein, mDab1, and show it is an adaptor molecule functioning in neural development. We find that mDab1 is expressed in certain neuronal and hematopoietic cell lines, and is localized to the growing nerves of embryonic mice. During mouse embryogenesis, mDab1 is tyrosine phosphorylated when the nervous system is undergoing dramatic expansion. However, when nerve tracts are established, mDab1 lacks detectable phosphotyrosine. Tyrosine-phosphorylated mDab1 associates with the SH2 domains of Src, Fyn and Abl. An interaction between mDab1 and Src is observed when P19 embryonal carcinoma (EC) cells undergo differentiation into neuronal cell types. mDab1 can also form complexes with cellular phosphotyrosyl proteins through a domain that is related to the phosphotyrosine binding (PTB) domains of the Shc family of adaptor proteins. The mDab1 PTB domain binds to phosphotyrosine-containing proteins of 200, 120 and 40 kDa from extracts of embryonic mouse heads. The properties of mDab1 and genetic analysis of Dab in Drosophila suggest that these molecules function in key signal transduction pathways involved in the formation of neural networks.     

High-Resolution Physical Map of the X-linked Retinoschisis Interval in Xp22

X-linked retinoschisis (RS) is the leading cause of macular degeneration in young males and has been mapped to Xp22 between DXS418 and DXS999. To facilitate identification of the RS gene, we have constructed a yeast artificial chromosome (YAC) contig across this region comprising 28 YACs and 32 sequence-tagged sites including seven novel end clone markers. To establish the definitive marker order, a PAC contig containing 50 clones was also constructed, and all clones were fingerprinted. The marker order is: Xpter–DXS1317–(AFM205yd12–DXS7175–DXS7992)–60N8T7–DXS1195–DXS7993–DXS7174–60N8-SP6–DXS418–DXS7994–DXS7995–DXS7996–HYAT2–25HA10R–HYAT1–DXS7997–DXS7998–DXS257–434E8R–3542R–DXS6762–DXS7999–DXS6763–434E8L–DXS8000–DXS6760–DXS7176–DXS8001–DXS999–3176R–PHKA2–Xcen. A long-range restriction map was constructed, and the RS region is estimated to be 1300 kb, containing three putative CpG islands. An unstable region was identified between DXS6763 and 434E8L. These data will facilitate positional cloning of RS and other disease genes in Xp22.     

Lactate dehydrogenase (LDH) gene duplication during chordate evolution: the cDNA sequence of the LDH of the tunicate Styela plicata

L-Lactate dehydrogenase (L-LDH, E.C. 1.1.1.27) is encoded by two or three loci in all vertebrates examined, with the exception of lampreys, which have a single LDH locus. Biochemical characterizations of LDH proteins have suggested that a gene duplication early in vertebrate evolution gave rise to Ldh-A and Ldh-B and that an additional locus, Ldh-C arose in a number of lineages more recently. Although some phylogenetic studies of LDH protein sequences have supported this pattern of gene duplication, others have contradicted it. In particular, a number of studies have suggested that Ldh-C represents the earliest divergence among vertebrate LDHs and that it may have diverged from the other loci well before the origin of vertebrates. Such hypotheses make explicit statements about the relationship of vertebrate and invertebrate LDHs, but to date, no closely related invertebrate LDH sequences have been available for comparison. We have attempted to provide further data on the timing of gene duplications leading to multiple vertebrate LDHs by determining the cDNA sequence of the LDH of the tunicate Styela plicata. Phylogenetic analyses of this and other LDH sequences provide strong support for the duplications giving rise to multiple vertebrate LDHs having occurred after vertebrates diverged from tunicates. The timing of these LDH duplications is consistent with data from a number of other gene families suggesting widespread gene duplication near the origin of vertebrates. With respect to the relationships among vertebrate LDHs, our data are not consistent with previous claims that Ldh-C represented the earliest divergence. However, the precise relationships among some of the main lineages of vertebrate LDHs were not resolved in our analyses.      

"This Job Is Harder Than It Looks": Rural Oaxacan Women Explain Why They Became Teachers

During the past six decades, rural women throughout the southeastern state of Oaxaca, Mexico, have comprised a significant percentage (currently the majority) of primary teachers. This article demonstrates that this phenomenon is a result of intertwining socioeconomic factors. It examines why expansion of the education system and economic opportunities may contribute to declining enrollment in teacher training programs even though the career remains a viable, and even desirable, choice for certain rural women.