Seed viability in declining populations of Caladenia rigida (Orchidaceae): are small populations doomed?

Despite comparatively good rates of pollination and seed production, some populations of the endangered terrestrial orchid Caladenia rigida continue to decline. To determine whether seed quality may be limiting reproductive potential, we assessed seed viability among declining populations of C. rigida (in the southern part of its distribution) and among populations that are regarded as stable (in the northern part of its distribution). We also compared differences in seed viability to plant traits, population size and habitat characteristics (soil properties, canopy cover, presence of proximate vegetation). Seed capsules from southern populations were significantly smaller, with only 9% of seeds being viable, compared to 36% in capsules from northern populations. Soil phosphorus concentrations differed between regions, but other habitat characteristics did not correlate with seed viability. Using calculations based on seedling recruitment data from other Caladenia species, we predict that seed output is insufficient to ensure the long-term persistence of the smallest C. rigida populations.

Histone variant H2A.Z is required for early mammalian development.

Fundamental to the process of mammalian development is the timed and coordinated regulation of gene expression. This requires transcription of a precise subset of the total complement of genes. It is clear that chromatin architecture plays a fundamental role in this process by either facilitating or restricting transcription factor binding [1]. How such specialized chromatin structures are established to regulate gene expression is poorly understood. All eukaryotic organisms contain specialized histone variants with distinctly different amino acid sequences that are even more conserved than the major core histones [2]. On the basis of their highly conserved sequence, histone variants have been assumed critical for the function of mammalian chromatin; however, a requirement for a histone variant has not been shown in mammalian cells. Mice with a deletion of H1 degrees have been generated by gene targeting in ES cells, but these mice show no phenotypic consequences, perhaps due to redundancy of function [3]. Here we show for the first time that a mammalian histone variant, H2A.Z, plays a critical role in early development, and we conclude that this histone variant plays a pivotal role in establishing the chromatin structures required for the complex patterns of gene expression essential for normal mammalian development.

In vitro development of porcine nuclear transfer embryos constructed using fetal fibroblasts.

The in vitro development of porcine nuclear transfer embryos constructed using primary cultures from day 25 fetal fibroblasts which were either rapidly dividing (cycling) or had their cell-cycle synchronized in G0/G1 using serum starvation (serum-starved) was examined. Oocyte-karyoplast complexes were fused and activated simultaneously and then cultured in vitro for seven days to assess development. Fusion rates were not different for either cell population. The proportion of reconstructed embryos that cleaved was higher in the cycling group compared to the serum-starved group (79 vs. 56% respectively; P < 0.05). Development to the 4-cell stage was not different using either population. Both treatments supported similar rates of development to the morula (1.5 vs. 7%, cycling vs. serum-starved) and blastocyst stage (1.5 vs. 3%, cycling vs. serum-starved). The blastocyst produced using cycling cells had a total cell number of 10. Total cell numbers for the three blastocysts produced serum-starved cells were 22, 24, and 33. These blastocysts had inner cell mass numbers of 0, 15, and 4, respectively. Six hundred and thirty-five nuclear transfer embryos reconstructed using serum-starved cells were transferred to 15 temporarily mated recipients for 3-4 days. Of these, 486 were recovered (77% recovery rate) of which 106 (22%) had developed to the 4-cell stage or later. These were transferred to a total of 15 recipients which were either unmated or mated. Seven recipients farrowed a total of 51 piglets. Microsatellite analysis revealed that none of these were derived from the nuclear transfer embryos transferred.

Comparison of the promoter proximal regions of the toxin-co-regulated tcp gene cluster in classical and El Tor strains of Vibrio cholerae O1.

A physical map has been constructed of the 5-kb XbaI fragment encoding the promoter proximal of region the tcp gene cluster encoding the toxin-coregulated pilus (TCP) of Vibrio cholerae. This fragment contains the major regulatory regions for TCP. Comparison of the nucleotide (nt) sequences from strains of the classical and El Tor biotypes demonstrates that the regions are essentially identical, with several notable exceptions. The intergenic regions, between tcpI and tcpP, and between tcpH and tcpA, show significant sequence divergence which may account for the biotype-related differences in TCP, since this is the location of the major promoter sequences. The C-terminal coding regions of the major pilin subunit, TcpA, also differ. Southern hybridization analyses suggest that the tcpA nt sequence is conserved within a biotype, and Western blot analysis suggests that the two forms of TcpA are antigenically different, but related. Besides tcpA, tcpB, tcpH and tcpI, the genes encoding two additional proteins, TcpP and TcpQ, but not previously defined, were also identified. TcpH and TcpI have been previously suggested to be regulatory proteins but homology data imply that TcpI is a methyl-accepting chemotaxis protein (MCP), as recently reported [Harkey et al., Infect. Immun. 62 (1994) 2669-2678], and TcpH is predicted to be a periplasmic or exported protein. TcpP is thought to be a trans-cytoplasmic membrane (CM) protein which may have a regulatory role.

Luteinizing hormone/chorionic gonadotropin bioactivity in the common marmoset (Callithrix jacchus) is due to a chorionic gonadotropin molecule with a structure intermediate between human chorionic gonadotropin and human luteinizing hormone.

Chorionic gonadotropin (CG), a pregnancy-specific heterodimeric hormone found in primates, is responsible for CL rescue with pregnancy maintenance. Of the primates, the human and baboon gene sequences are the only structures so far determined. In order to study the structure and function of CG in other primates, we have isolated and sequenced the coding regions for the two subunits of marmoset CG (mCG) by the reverse transcription/polymerase chain reaction method. Study of multiple clones confirmed a high degree of homology with the human sequences (88% and 80% for the alpha and beta nucleotide sequences, respectively). Marmoset CG alpha has an extra four amino acids compared to hCG alpha, whereas the mCG beta sequence has a 3-bp deletion that maintains the reading frame and C-terminal amino acid sequence. Most of the differences between hCG beta and mCG beta peptides occur in the C-terminal region, which includes the loss of two of the O-linked glycosylation consensus sequences and the presence of an N-linked glycosylation consensus sequence. When mCG alpha and beta were co-expressed in CHO cells, assembly of biologically active hormone was confirmed by induced steroid secretion by MA10 cells. Partially purified mCG beta was used to raise anti-mCG antibodies. To date, an antibody has been obtained that is capable of detecting recombinant mCG beta, recombinant mCG dimer, and mCG dimer secreted by cultured marmoset trophoblast. Marmoset CG alpha and beta were also detectable at the transcriptional level in cultured trophoblast by in situ hybridization. This suggests that the LH/CG bioactivity reported from marmoset placentae and embryos is due to a molecule with structural features common to hLH (glycosylation pattern) and hCG (CG beta C-terminal structure).

Nucleotide sequence of the structural gene, tcpA, for a major pilin subunit of Vibrio cholerae.

The toxin co-regulated pilus (Tcp) of Vibrio cholerae appears to be a major protective antigen. By cosmid cloning we have isolated a number of clones capable of converting Tcp- El Tor strains of V. cholerae to Tcp+. A synthetic oligodeoxyribonucleotide probe based upon the N-terminal amino acid sequence of TcpA, has been used to localize the structural gene within the cosmid clones. Using suitable subclones, the nucleotide sequence of the tcpA gene has been determined. The gene encodes a 23.3-kDa pre-protein which in its mature form has a size of 20.3 kDa. The N-terminal leader peptide or signal sequence is atypical and does not conform with the usual rules of such sequences. The TcpA protein shows some similarities to the major pilins of the methylated phenylalanine type or type-4 pili from other bacteria; however, it is sufficiently different that it may represent a new class.