Genes, development and evolution of the placenta.

Through studies of transgenic and mutant mice, it is possible to describe molecular pathways that control the development of all major trophoblast cell subtypes and structures of the placenta. For example, the proliferation of trophoblast stem cells is dependent on FGF signalling and downstream transcription factors Cdx2, Eomes and Err2. Several bHLH transcription factors regulate the progression from trophoblast stem cells to spongiotrophoblast and to trophoblast giant cells (Id1/2, Mash2, Hand1, Stra13). Intercellular actions critical for maintaining stable precursor cell populations are dependent on the gap junction protein Cx31 and the growth factor Nodal. Differentiation towards syncytiotrophoblast as well as the initiation of chorioallantoic (villous) morphogenesis is regulated by the Gcm1 transcription factor, and subsequent labyrinth development is dependent on Wnt, HGF and FGF signalling. These insights suggest that most of the genes that evolved to regulate placental development are either identical to ones used in other organ systems (e.g., FGF and epithelial branching morphogenesis), were co-opted to take on new functions (e.g., AP-2gamma, Dlx3, Hand1), or arose via gene duplication to take on a specialized placental function (e.g., Gcm1, Mash2). Many of the human orthologues of these critical genes show restricted expression patterns that are consistent with a conserved function. Such information is aiding the comparison of the human and mouse placenta. In addition, the prospect of a conserved function clearly suggests potential mechanisms for explaining complications of human placental development.

Identification and characterization of a cystathionine beta/gamma-lyase from Lactococcus lactis ssp. cremoris MG1363.

This paper describes the nucleotide sequence of a gene encoding cystathionine beta/gamma-lyase from Lactococcus lactis ssp. cremoris MG1363, its overexpression in Escherichia coli and some functional characteristics of the purified recombinant protein.

The nature of hematological response in fish : Studies on rainbow troutOncorhynchus mykiss exposed to simulated winter, spring and summer conditions.

Hematological status was examined in rainbow trout,Oncorhynchus mykiss, held for 3-4 weeks under temperature, photoperiod and PO 2 conditions approximating those of their winter, spring and summer habitats. The most striking change observed was in red cell population composition. In 'winter' fish mature cells were predominant; juvenile and developing erythrocytes characterized 'spring' and 'summer' animals. Hemoglobin, hematocrit and both mean erythrocytic volume and hemoglobin were modestly lower in 'spring' and 'summer' than in 'winter' fish. Red cell numbers were not significantly affected. These observations suggest that avoidance of viscosity-based increases in circulatory work cost is more advantageous than elevation of blood O2-carrying capacity. Although hemoglobin isomorph profiles were significantly altered, there is little evidence that such changes are of critical adaptive importance. Given presumed age-based reduction in gas transport effectiveness, the replacement of mature and senescent cells by more metabolically-competent juvenile cells appears to be the pivotal event in hematological response. Leucocyte counts were significantly elevated in 'spring' and 'summer' as compared to 'winter' fish. Lymphocyte/heterophil ratios declined from 8.27 in 'winter' fish to 3.13 in 'summer' trout. Thrombocyte, monocyte, eosinophil and basophil abundances were little changed.

Mitochondrial-DNA sequence evidence on the phylogeny of Australian jack-jumper ants of the Myrmecia pilosula complex.

Australian ants of the Myrmecia pilosula species complex include some individuals (in M. croslandi) with the lowest possible metazoan chromosome number of 2n = 2. Others in this cluster of sibling species have much higher numbers, the known maximum being 2n = 32. Two species (M. pilosula and M. 'banksi') are believed on cytogenetic and morphological grounds to have hybridized over a long period. To investigate the phylogeny and age of this group relative to the congeneric outgroup species M. gulosa, we sequenced part of the cytochrome b gene and the intergenic sequence between it and a primer anchored on the nearby tRNA(UCNSer) gene and analyzed the coding region using bootstrapped parsimony and neighbor-joining trees using the numbers of synonymous and nonsynonymous codons per site. The intergenic space demonstrated a profusion of repeated sequences, and only very closely related sequences (as judged by that for cytochrome b) showed detectable similarity at this almost 100% A+T region. In agreement with predictions from karyotype studies, the phylogenetic analyses showed that M. croslandi is the sister group to the other siblings; the time of separation of M. croslandi from the rest of the pilosula group is unexpectedly ancient. Other relationships were poorly resolved, but the results suggest that M. 'banski' and M. pilosula cluster together, as expected on cytogenetic grounds, and the tentative suggestion of close affinity of the M. pilosula samples and two "PB" samples supports derivation of PB from female M. pilosula and male M. 'banksi.'