Abnormal cardiac inflow patterns during postnatal development in a mouse model of Holt-Oram syndrome

Tbx5(del/+) mice provide a model of human Holt-Oram syndrome. In this study, the cardiac functional phenotypes of this mouse model were investigated with 30-MHz ultrasound by comparing 12 Tbx5(del/+) mice with 12 wild-type littermates at 1, 2, 4, and 8 wk of age. Cardiac dimensions were measured with two-dimensional and M-mode imaging. The flow patterns in the left and right ventricular inflow channels were evaluated with Doppler flow sampling. Compared with wild-type littermates, Tbx5(del/+) mice showed significant changes in the mitral flow pattern, including decreased peak velocity of the left ventricular (LV) early filling wave (E wave), increased peak velocity of the late filling wave (A wave), and decreased or even reversed peak E-to-A ratio. The prolongation of LV isovolumic relaxation time was detected in Tbx5(del/+) neonates as early as 1 wk of age. In Tbx5(del/+) mice, LV wall thickness appeared normal but LV chamber dimension was significantly reduced. LV systolic function did not differ from that in wild-type littermates. In contrast, the Doppler flow spectrum in the enlarged tricuspid orifice of Tbx5(del/+) mice demonstrated increased peak velocities of both E and A waves and increased total time-velocity integral but unchanged peak E/A. In another 13 mice (7 Tbx5(del/+), 6 wild-type) at 2 wk of age, significant correlation was found between Tbx5 gene expression level in ventricular myocardium and LV filling parameters. In conclusion, the LV diastolic function of Tbx5(del/+) mice is significantly deteriorated, whereas the systolic function remains normal.     

Nutritional and Morphological Traits of Invasive and Exotic Fleshy‐fruits in South Africa

While fleshy‐fruited invasive alien plants are recognized as some of the worst invaders on a global scale, until recently, little consideration has been given to the frugivores that feed on these fruits and, more specifically, the fruit traits, which may influence this. We investigated a series of morphological and nutritive fruit traits for ca 30 species of fleshy‐fruited invasive alien and exotic species in South Africa. Invasive alien fruit traits were compared with comparable traits of a similar sample size of indigenous fleshy fruits, which occur in the same area. Finally, the similarity of traits for the same invasive alien species was compared with those fruits in Australia. Invasive alien fleshy fruits were similar in morphology, but greater in some nutritive aspects when compared with indigenous fruits. Furthermore, they were very similar in all aspects to their counterparts in Australia. Most seeds of invasive fleshy fruits were small and light, which may explain some of their invasive success, as benefits associated with small seededness may promote invasive potential. Nutritionally, most invasive alien fleshy‐fruits were hexose‐dominant, containing low lipid and nitrogen content. While frugivore preference trends remain to be formally investigated, this study provides insights into fruit traits, which may tentatively outline why invasive fruits are universally fed on and thus successfully spread.     

Fifteen years of annual Cape Parrot Poicephalus robustus censuses: current population trends and conservation contributions

The Cape Parrot Poicephalus robustus is endemic to South Africa and numbers have reportedly declined since the early 1900s. It is a forest specialist and food nomadic, moving between patches depending on fruit availability. This makes it difficult to estimate numbers accurately and to determine its distribution. The annual Cape Parrot Big Birding Day was initiated in 1998 as a national census to determine a population estimate. Volunteers assist in monitoring and counting the Cape Parrot in the Eastern Cape, KwaZulu-Natal and Limpopo provinces in indigenous forests as well as sites where the parrots are known to feed outside of forests. Here, a summary of 15 years of census data is presented. In all years, with the exception of 2009, less than 1 600 Cape Parrots were recorded in the wild. The census data showed a slight increase in Cape Parrots, although this may be largely explained by an increase in coverage of suitable habitat and stabilisation in the population since 2005. A current distribution map for the Cape Parrot, based on census data, is presented. The distribution remains largely unchanged from that presented in the 1970s. This study highlights the value of public participation in monitoring an Endangered species and the need to conserve the forests where these parrots occur, due to their nomadic feeding behaviour.     

Hunting flight speeds of five southern African raptors

The flight speeds of hunting falconry birds were determined using global positioning system data loggers. Until now, the hunting flight speed of African raptors has not been directly measured. We predicted that hunting flight speeds would differ between species and that flight dynamics, such as altitude, and bird morphology, particularly wing surface area, would influence maximum and mean flight speeds. This study considered five African raptor species, which included two long-wing species, Lanner Falcon Falco biarmicus and Peregrine Falcon F. peregrinus, one short-wing species, Black Sparrowhawk Accipiter melanoleucus, and two broad-wing species, African Hawk-eagle Aquila spilogaster and Jackal Buzzard Buteo rufofuscus. Maximum and mean hunt speeds differed significantly between the long- and short-wing species. There was no difference in acceleration or deceleration rates between these species, but this could be due to small sample sizes. There was a significant positive correlation between maximum hunt speed and maximum flight height for the long-wing species. Maximum and mean flight speeds were significantly negatively correlated with wing area for all five species in this study. However, following phylogenetic correction, no significant relationship between wing area and maximum hunt speeds was found. This study presents baseline data of hunting speeds in African raptors and further highlights the importance of inter-species variation, which can provide accuracy to flight speed models and the understanding of hunting strategies.     

Meiotic recombination and spatial proximity in the etiology of the recurrent t(11;22)

Although balanced translocations are among the most common human chromosomal aberrations, the constitutional t(11;22)(q23;q11) is the only known recurrent non-Robertsonian translocation. Evidence indicates that de novo formation of the t(11;22) occurs during meiosis. To test the hypothesis that spatial proximity of chromosomes 11 and 22 in meiotic prophase oocytes and spermatocytes plays a role in the rearrangement, the positions of the 11q23 and 22q11 translocation breakpoints were examined. Fluorescence in situ hybridization with use of DNA probes for these sites demonstrates that 11q23 is closer to 22q11 in meiosis than to a control at 6q26. Although chromosome 21p11, another control, often lies as close to 11q23 as does 22q11 during meiosis, chromosome 21 rarely rearranges with 11q23, and the DNA sequence of chromosome 21 appears to be less susceptible than 22q11 to double-strand breaks (DSBs). It has been suggested that the rearrangement recurs as a result of the palindromic AT-rich repeats at both 11q23 and 22q11, which extrude hairpin structures that are susceptible to DSBs. To determine whether the DSBs at these sites coincide with normal hotspots of meiotic recombination, immunocytochemical mapping of MLH1, a protein involved in crossing over, was employed. The results indicate that the translocation breakpoints do not coincide with recombination hotspots and therefore are unlikely to be the result of meiotic programmed DSBs, although MRE11 is likely to be involved. Previous analysis indicated that the DSBs appear to be repaired by a mechanism similar to nonhomologous end joining (NHEJ), although NHEJ is normally suppressed during meiosis. Taken together, these studies support the hypothesis that physical proximity between 11q23 and 22q11--but not typical meiotic recombinational activity in meiotic prophase--plays an important role in the generation of the constitutional t(11;22) rearrangement.     

An investigation of the basis of a current hypothesis for the lack of G-banding in plant chromosomes

A current hypothesis for the lack of G-banding in plant chromosomes is based on the assumption that plant chromosomes are more compact than animal chromosomes. We tested the basis of the hypothesis by measuring lengths and volumes of plant and animal chromosomes that had been similarly treated. We conclude there is no consistent difference in the compaction of plant vs animal chromosomes.     

The formation of the central element of the synaptonemal complex may occur by multiple mechanisms: the roles of the N- and C-terminal domains of the Drosophila C(3)G protein in mediating synapsis and recombination

In Drosophila melanogaster oocytes, the C(3)G protein comprises the transverse filaments (TFs) of the synaptonemal complex (SC). Like other TF proteins, such as Zip1p in yeast and SCP1 in mammals, C(3)G is composed of a central coiled-coil-rich domain flanked by N- and C-terminal globular domains. Here, we analyze in-frame deletions within the N- and C-terminal regions of C(3)G in Drosophila oocytes. As is the case for Zip1p, a C-terminal deletion of C(3)G fails to attach to the lateral elements of the SC. Instead, this C-terminal deletion protein forms a large cylindrical polycomplex structure. EM analysis of this structure reveals a polycomplex of concentric rings alternating dark and light bands. However, unlike both yeast and mammals, all three proteins deleted for N-terminal regions completely abolished both SC and polycomplex formation. Both the N- and C-terminal deletions significantly reduce or abolish meiotic recombination similarly to c(3)G null homozygotes. To explain these data, we propose that in Drosophila the N terminus, but not the C-terminal globular domain, of C(3)G is critical for the formation of antiparallel pairs of C(3)G homodimers that span the central region and thus for assembly of complete TFs, while the C terminus is required to affix these homodimers to the lateral elements.     

A weak effect of background selection on trinucleotide microsatellites in maize

Artificial selection during the domestication of maize is thought to have been predominantly positive and to have had little effect on the surrounding neutral diversity because linkage disequilibrium breaks down rapidly when physical distance increases. However, the degree to which indirect selection has shaped neutral diversity in the maize genome during domestication remains unclear. In this study, we investigate the relationship between local recombination rate and neutral polymorphism in maize and in teosinte using both sequence and microsatellite data. To quantify diversity, we estimate 3 parameters expected to differentially reflect the effects of indirect selection and mutation. We find no general correlation between diversity and recombination, indicating that indirect selection has had no genome-wide impact on maize diversity. However, we detect a weak correlation between heterozygosity and recombination for trinucleotide microsatellites deviating from the stepwise mutation model and located within genes (rho = 0.32, P < 0.03). This result can be explained by a background selection hypothesis. The fact that the same correlation is not confirmed for nucleotide diversity suggests that the strength of purifying selection at or near this class of microsatellites is higher than for nucleotide mutations.     

Protein kinase activities in ripening mango (Mangifera indica) fruit tissue. II. Purification and characterization of a casein kinase I

A protein kinase (PK‐II), phosphorylating casein, was purified from ripening mango, Mangifera indica L., fruit tissue. The purification procedure consisted of ammonium sulphate fractionation and sequential anion exchange‐, dye‐ligand, and gel filtration chromatography. The enzyme was purified over 500‐fold to near homogeneity with a recovery of 4%. The purified enzyme had a specific activity of ca 1 µmol mg⁻¹ protein min⁻¹ with ATP as phosphoryl donor. SDS‐PAGE results indicated a monomeric enzyme with molecular mass of 35 kDa. The protein kinase phosphorylated the acidic substrates casein and phosvitin, but had a very low activity with histones and protamine sulphate. The optimum pH and temperature for catalysis were determined to be 9.6 and 35°C, respectively. Mn²⁺ could not substitute for the Mg²⁺ needed for activity and Ca²⁺ had a slight stimulatory effect. Phospholipids, cAMP, calmodulin and the calmodulin inhibitor, calmidazolium, did not have any significant effect on activity, but the enzyme was inhibited by heparin and the specific inhibitor, CKI‐7, ( N ‐[2‐aminoethyl]‐5‐chloroisoquinoline‐8‐sulphonamide). Autoradiographic studies revealed the ability of the protein kinase to autophosphorylate as well as the presence of endogenous protein substrates in the crude extract. Initial velocity studies with casein as substrate and product inhibition studies with ADP indicated a K_m (ATP) and K_m (casein) of 14 µ M and 0.18 mg ml⁻¹, respectively, with a K_i (ADP) of 3.2 µM. The enzyme can be classified as a casein kinase I type of protein kinase (EC 2.7.10).