Dynamic shapes of the zygote and two-cell mouse and human.

Mouse zygote morphokinetics were measured during interphase, the mitotic period, cytokinesis, and two-cell stage. Sequences of rounder-distorted-rounder shapes were revealed, as were changing patterns of cross section area. A calcium chelator and an actin-disrupting agent inhibited the area changes that occurred between pronuclear envelope breakdown and cytokinesis. During cell division, two vortices developed in each nascent cell and they rotated in opposite directions at each end of the cell, a pattern that sometimes persisted for up to 10 h. Exchange with the environment may have been promoted by these shape and area cycles and persisting circulation in the cytoplasm may have a similar function between a cell's interior and periphery. Some of these movements were sporadically also seen in human zygotes with abnormal numbers of pronuclei and the two-cell stages that developed from these compromised human zygotes.

Combining MALDI-TOF and genomics in the study of methicillin resistant and multidrug resistant Staphylococcus pseudintermedius in New Zealand.

Staphylococcus pseudintermedius is an opportunistic and emerging zoonotic pathogen that primarily colonises the skin of dogs. Many common variants are methicillin resistant (MRSP) or multidrug resistant (MDR), and drug resistance is increasingly reported across the globe. In New Zealand, MRSP isolation remains rare in clinics. To pre-emptively inform diagnostic and antimicrobial stewardship practices, we examine isolates of S. pseudintermedius, MRSP and MDR-MRSP from New Zealand dogs using a combination of methodologies. Genetic and genomic data combined with antimicrobial susceptibility screening identify common drug-resistance profiles and their genetic determinants. We demonstrate that sensitive and specific species-level identification of S. pseudintermedius can be achieved using Bruker MALDI-TOF MS and, further, that this technique can be used to identify some common subtype variants, providing a level of categorical precision that falls somewhere between single-locus and multi-locus sequence typing. Comparative genomics analysis of global S. pseudintermedius data shows that MRSP moves frequently across the globe, but that horizontal gene transfer events resulting in the acquisition of the SCCmec cassette (responsible for beta-lactam antibiotic resistance) are infrequent. This suggests that biosecurity and surveillance in addition to antibiotic stewardship should play important roles in mitigating the risk of MRSP, especially in countries such as New Zealand where MRSP is still rare.

Theoretical exploration of blastocyst morphogenesis.

A theoretical exploration of cell distribution on the mouse blastocyst is conducted. A model ball of cells represents the morula which develops into a 32-cell model blastocyst that is enclosed in a spherical surface with a hemispherical cavity at one end. In the combinatorial analysis it is assumed that each cell of the 2-cell embryo forms 16 cells in the blastocyst and that these 16 cells touch each other. The results of the analysis identify a tendency for one set of 16 cells to contribute twice as many cells to the basal solid end of the blastocyst than the other set, a developmental bias that is also found by some observers of natural blastocysts. In the geometric analysis, half the volume of the inner group of cells of the morula and blastocyst and half the volume of the surrounding shell cells, the trophectoderm, is assumed to be formed from the progeny of each 2-cell stage cell. Making various assumptions about morphogenesis, it is found that there is a tendency for a curved frontier between the volumes from each 2-cell stage cell, the clonal volumes, to lie at an angle of 43.4 degrees to the equator of the blastocyst and for the bulk of the frontier circumference to lie on either side of the equator. These tendencies are also found by some observers of real blastocysts.

Andrzej Krzysztof Tarkowski abroad, in photos and correspondence.

An informal account records the remaining traces of Tarkowski's research visits to the United Kingdom and France. The account has many authors and it should not be regarded as an exact history. The early 1960s began with the dramatic production of chimaeras at the University of Bangor and the long term exchange of information with Anne McLaren's Edinburgh laboratory. The techniques of parthenogenesis and nuclear transfer became the obsession of the 1970's and Tarkowski pursued the problem in Oxford (U.K.), in France, and with his group in Warsaw (Poland). A variant of this theme emerged during the 1980's and this was attempts to produce interspecies hybrids in Oxford and Warsaw. During the 1990's, the Warsaw laboratory became sufficiently well funded to make his trips unnecessary and his pupils became a Polish Diaspora of Embryologists.

Two ENU-induced mutations in Rasgrf1 and early mouse growth retardation.

When paternally transmitted, two independent ENU-induced mutations showed reduced whole body wet weight soon after birth. The mutations were mapped to Chromosome 9 (Chr 9) between the markers D9Mit208 and D9Mit215. Their map position and imprinted status suggested that they might alter RAS protein-specific guanine nucleotide releasing factor 1 expression. Both mutations introduced premature chain termination codons into the coding sequence of Rasgrf1, and no Ras-GRF1 protein was detected in the brain. The GENA53 line had a C to T transition at nucleotide 2137, and the line GENA37 had a T to A transversion at nucleotide 3552 of the cDNA sequence. Mutant mice had near normal body weight at birth, but their weight started to lag behind that of wild-type littermates during the first week, and they were about 15% lighter as adults.