Inactivation of Btk by insertion of lacZ reveals defects in B cell development only past the pre-B cell stage.

Bruton's tyrosine kinase (Btk) is a cytoplasmic protein kinase that is defective in X-linked agammaglobulinaemia in man and in X-linked immunodeficiency in the mouse. There is controversy regarding the stages of B cell development that are dependent on Btk function. To determine the point in B cell differentiation at which defects in Btk become apparent, we generated a mouse model by inactivating the Btk gene through an in-frame insertion of a lacZ reporter by homologous recombination in embryonic stem cells. The phenomenon of X-chromosome inactivation in Btk+/- heterozygous female mice enabled us to evaluate the competition between B cell progenitors expressing wild-type Btk and those expressing the Btk-/lacZ allele in each successive step of development. Although Btk was already expressed in pro-B cells, the first selective disadvantage only became apparent at the transition from small pre-B cells to immature B cells in the bone marrow. A second differentiation arrest was found during the maturation from IgD(low)IgM(high) to IgD(high)IgM(low) stages in the periphery. Our results show that Btk expression is essential at two distinct differentiation steps, both past the pre-B cell stage.     

Patterns of sequence variation in the mitochondrial D-loop region of shrews

Direct sequencing of the mitochondrial displacement loop (D-loop) of shrews (genus Sorex) for the region between the tRNA(Pro) and the conserved sequence block-F revealed variable numbers of 79-bp tandem repeats. These repeats were found in all 19 individuals sequenced, representing three subspecies and one closely related species of the masked shrew group (Sorex cinereus cinereus, S. c. miscix, S. c. acadicus, and S. haydeni) and an outgroup, the pygmy shrew (S. hoyi). Each specimen also possessed an adjacent 76-bp imperfect copy of the tandem repeats. One individual was heteroplasmic for length variants consisting of five and seven copies of the 79-bp tandem repeat. The sequence of the repeats is conducive to the formation of secondary structure. A termination-associated sequence is present in each of the repeats and in a unique sequence region 5' to the tandem array as well. Mean genetic distance between the masked shrew taxa and the pygmy shrew was calculated separately for the unique sequence region, one of the tandem repeats, the imperfect repeat, and these three regions combined. The unique sequence region evolved more rapidly than the tandem repeats or the imperfect repeat. The small genetic distance between pairs of tandem repeats within an individual is consistent with a model of concerted evolution. Repeats are apparently duplicated and lost at a high rate, which tends to homogenize the tandem array. The rate of D- loop sequence divergence between the masked and pygmy shrews is estimated to be 15%-20%/Myr, the highest rate observed in D-loops of mammals. Rapid sequence evolution in shrews may be due either to their high metabolic rate and short generation time or to the presence of variable numbers of tandem repeats.      

Morphological phylogenetics of theAsteraceae-Asteroideae,with notes on character evolution

The relationships within theAsteraceae-Asteroideae are scrutinized by means of cladistic analyses of morphological and chemical data. New data are presented, and novel interpretations of features previously used in cladistic analyses are made. Examples are insertion of anther filaments in the corolla, and morphology of disc floret styles, respectively. The results include a polyphyletic or paraphyleticInuleae s. l., and a paraphyleticHeliantheae s.l. in which theEupatorieae constantly form a subclade. Comparisons are made with previous cladistic analyses of morphological data, and those acquired from molecular data. Speculations about the evolution of certain organs are presented.     

大鼠胼胝体内神经肽Y免疫反应阳性纤维的发育

本实验用免疫组织化学ＡＢＣ法研究了大鼠胼胝体内神经肽Ｙ免疫反应阳性（ＮＰＹ－ＩＲ）纤维的生后发育。结果发现,许多ＮＰＹ－ＩＲ纤维在大鼠出生时便存在于胼胝体内。ＮＰＹ－ＩＲ胼胝体纤维的密度在生后１周内继续逐渐增高,在第２周内达到最高峰。之后,ＮＰＹ－ＩＲ胼胝体纤维的密度逐渐下降,至第３周末时接近成年时的水平,即仅有少量ＮＰＹ－ＩＲ纤维存在于胼胝体内。这些结果提示在大鼠早期生后发育过程中许多ＮＰＹ－ＩＲ胼胝体纤维是暂时性的,其作用可能与大脑皮质的机能发育有关。     

Psednotrichia, a genus of the tribe Senecioneae hitherto misplaced in the Astereae (Asteraceae)

Anderberg, A. A. & Karis, P. O. 1995. Psednotrichia , a genus of the tribe Senecioneae hitherto misplaced in the Astereae (Asteraceae). — Nord. J. Bot. 15: 375–379. Copenhagen. ISSN 0107–055X.
The tribal position for the little known genus Psednorrichia , is established. This monotypic genus, hitherto placed in the tribe Astereae, is a congener of Xyridopsis of the tribe Senecioneae (Asteraceae). The two species of Xyridopsis are here transferred to Psednotrichia and the new combinations P. xyridopsis and P. newtonii are made. A brief discussion of the morphology of the genus, and its systematic position within the tribe Senecioneae is provided.     

Phylogeography of the widespread African puff adder (Bitis arietans) reveals multiple Pleistocene refugia in southern Africa

Evidence from numerous Pan‐African savannah mammals indicates that open‐habitat refugia existed in Africa during the Pleistocene, isolated by expanding tropical forests during warm and humid interglacial periods. However, comparative data from other taxonomic groups are currently lacking. We present a phylogeographic investigation of the African puff adder (Bitis arietans), a snake that occurs in open‐habitat formations throughout sub‐Saharan Africa. Multiple parapatric mitochondrial clades occur across the current distribution of B. arietans, including a widespread southern African clade that is subdivided into four separate clades. We investigated the historical processes responsible for generating these phylogeographic patterns in southern Africa using species distribution modelling and genetic approaches. Our results show that interior regions of South Africa became largely inhospitable for B. arietans during glacial maxima, whereas coastal and more northerly areas remained habitable. This corresponds well with the locations of refugia inferred from mitochondrial data using a continuous phylogeographic diffusion model. Analysis of data from five anonymous nuclear loci revealed broadly similar patterns to mtDNA. Secondary admixture was detected between previously isolated refugial populations. In some cases, this is limited to individuals occurring near mitochondrial clade contact zones, but in other cases, more extensive admixture is evident. Overall, our study reveals a complex history of refugial isolation and secondary expansion for puff adders and a mosaic of isolated refugia in southern Africa. We also identify key differences between the processes that drove isolation in B. arietans and those hypothesized for sympatric savannah mammals.