Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes

Statistical methods for computing the standard errors of the branching points of an evolutionary tree are developed. These methods are for the unweighted pair-group method-determined (UPGMA) trees reconstructed from molecular data such as amino acid sequences, nucleotide sequences, restriction-sites data, and electrophoretic distances. They were applied to data for the human, chimpanzee, gorilla, orangutan, and gibbon species. Among the four different sets of data used, DNA sequences for an 895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979) gave the least reliable one. The DNA sequence data suggested that the chimpanzee is the closest and that the gorilla is the next closest to the human species. The orangutan and gibbon are more distantly related to man than is the gorilla. This topology of the tree is in agreement with that for the tree obtained from chromosomal studies and DNA-hybridization experiments. However, the difference between the branching point for the human and the chimpanzee species and that for the gorilla species and the human-chimpanzee group is not statistically significant. In addition to this analysis, various factors that affect the accuracy of an estimated tree are discussed.      

Complementary Functioning of Nitrogenase Components from a Blue-Green Alga and a Photosynthetic Bacterium

Nitrogenases from Anabaena cylindrica and Chloropseudomonas ethylicum were partially purified into two components. A. cylindrica fraction I protein complemented fraction II protein from C. ethylicum. However, the reciprocal cross between C. ethylicum fraction I and A. cylindrica fraction II was negative.     

THE ROUTE OF ENTRY AND LOCALIZATION OF BLOOD PROTEINS IN THE OOCYTES OF SATURNIID MOTHS

The oocytes of saturniid moths take up proteins selectively from the blood. The distribution of blood proteins in the ovary during protein uptake was investigated by staining 2 µ sections of freeze-dried ovaries with fluorescein-labeled antibodies. The results indicate that blood proteins occur primarily in the intercellular spaces of the follicle cell layer, in association with a brush border at the surface of the oocyte, and within the oocyte in the yolk spheres. That proteins derived from the blood are associated with the yolk spheres was confirmed by isolating these bodies and showing that lysis, which can be induced by any of a number of mechanical means, causes them to release immunologically defined proteins known to be derived from the blood. That the level of blood proteins in the cytoplasm is low relatively to that in the yolk spheres was confirmed by the observation that the yellow pigments associated with several blood proteins, although conspicuous in the yolk spheres, are not visible in the translucent layer of centrifuged oocytes. From these and previous physiological observations, it is proposed that blood proteins reach the surface of the oocyte by an intercellular route, that they combine with some component of the brush border, and that they are transformed into yolk spheres by a process akin to pinocytosis.     

cAMP-stimulated termination of vitellogenesis in Hyalophora cecropia: formation of a diffusion barrier and the loss of patency

Activation of cAMP-dependent protein kinase (PKA) by cell-permeable analogs of cAMP causes early and mid-vitellogenic follicles of Hyalophora cecropia to terminate vitellogenin uptake [[Wang and Telfer, 1996], Insect Biochem. Mol. Biol. 26, 85-94 (1996)]. The response is shown here to entail the formation of an epithelial diffusion barrier. Follicle cells that have been loosely organized to provide intercellular pathways for the movement of vitellogenin to the oocyte surface transform into a tight epithelium within 1-2h of exposure to PKA activators. The follicle cells can now prevent the escape of Lucifer yellow CH that has been iontophoresed into the space surrounding the oocyte, and the entry of labeled vitellogenin from the medium. As they form this functional equivalent of a tight junction, the follicle cells further reduce the intercellular spaces by enlarging and pressing against each other, and by slowing the secretion of the sulfated glycosaminoglycan matrix that separates them during vitellogenesis. The activation of PKA in early and mid-vitellogenic follicles thus appears to trigger prematurely a set of changes that do not normally occur until the follicle has grown to a length of about 2.0mm.     

Mesodern-inducing factors and mesodermal patterning

Identification of the signalling molecules involved in mesoderm formation in amphibian embryos still presents problems. None of the original candidates, such as activin, have been definitively ruled out, and the new factors, such as the nodal-related genes, have come on to the scene. Of the original candidates, activin has been definitively shown to act as a morphogen, whereas bone morphogenetic protein (BMP)-4 has emerged as a ventral inducer and an inhibitor of neural differentiation. The effects of BMP-4 are antagonized by chordin, a molecule related to the product of the Drosophila gene short gastrulation.     

Mouse oocytes promote proliferation of granulosa cells from preantral and antral follicles in vitro.

Evidence is now emerging that the oocyte plays a role in the development and function of granulosa cells. This study focuses on the role of the oocyte in the proliferation of (1) undifferentiated granulosa cells from preantral follicles and (2) more differentiated mural granulosa cells and cumulus granulosa cells from antral follicles. Preantral follicles were isolated from 12-day-old mice, and mural granulosa cells and oocyte-cumulus complexes were obtained from gonadotropin-primed 22-day-old mice. Cell proliferation was quantified by autoradiographic determination of the 3H-thymidine labeling index. To determine the role of the oocyte in granulosa cell proliferation, oocyte-cumulus cell complexes and preantral follicles were oocytectomized (OOX), oocytectomy being a microsurgical procedure that removes the oocyte while retaining the three-dimensional structure of the complex or follicle. Mural granulosa cells as well as intact and OOX complexes and follicles were cultured with or without FSH in unconditioned medium or oocyte-conditioned medium (1 oocyte/microliter of medium). Preantral follicles were cultured for 4 days, after which 3H-thymidine was added to each group for a further 24 h. Mural granulosa cells were cultured as monolayers for an equilibration period of 24 h and then treated for a 48-h period, with 3H-thymidine added for the last 24 h. Oocyte-cumulus cell complexes were incubated for 4 h and then 3H-thymidine was added to each group for an additional 3-h period. FSH and/or oocyte-conditioned medium caused an increase in the labeling index of mural granulosa cells in monolayer culture; however, no differences were found among treatment groups.(ABSTRACT TRUNCATED AT 250 WORDS)