Molecular cloning of the bovine thymopoietin gene and its expression in different calf tissues: evidence for a predominant expression in thymocytes

Comparative gene expression analysis of bovine nuclear-transferred embryos with different developmental potential by cDNA microarray and real-time PCR to determine genes that might reflect calf normality

Placental abnormalities are the main factor in the high incidence of somatic cell clone abnormalities. The expression of several trophoblast cell-specific molecules is enhanced during gestational days 7 to 14. To determine the possible genes whose expression patterns might reflect calf normality, we first compared the gene expression profiles on day 15 between in vitro-fertilized (IVF) embryos and two types of somatic cell nuclear-transferred embryos with either a high (FNT) or low (CNT) incidence of neonatal abnormalities using a cDNA microarray containing 16 of 21 placenta-specific genes developed from tissues collected across gestation. To identify significant genes from the screening of day 15 embryos, genes with a less than two-fold difference in expression between IVF and CNT embryos, and those with a greater than two-fold difference between IVF and FNT and between CNT and FNT were considered to contribute to clone abnormalities. These two comparisons revealed 18 down-regulated and 18 upregulated genes of the 1722 genes examined. We then examined the expression levels of 10 genes with known functions in eight-cell and blastocyst-stage embryos by real-time PCR. The mRNA expression pattern of interferon (IFN)-tau, a trophectoderm-related gene, differed between IVF, CNT, and FNT eight-cell embryos; few or none of the IVF or CNT eight-cell embryos expressed IFN-tau mRNA, but all eight-cell FNT embryos expressed IFN-tau. IFN-tau mRNA expression was significantly higher in IVF blastocysts, however, than in nuclear-transferred blastocysts. Average IFN-tau mRNA expression in FNT blastocysts was not different from that in CNT blastocysts, due to one CNT blastocyst with high expression. The precise relation between early expression of IFN-tau mRNA and inferior developmental potential in cloned embryos should be examined further.

TPX2 is required for postmitotic nuclear assembly in cell-free Xenopus laevis egg extracts

Cell division in many metazoa is accompanied by the disassembly of the nuclear envelope and the assembly of the mitotic spindle. These dramatic structural rearrangements are reversed after mitosis, when the mitotic spindle is dismantled and the nuclear envelope reassembles. The targeting protein for XKlp2 (TPX2) plays important roles in mitotic spindle assembly. We report that TPX2 depletion from nuclear assembly extracts prepared from Xenopus laevis eggs results in the formation of nuclei that are only about one fifth the size of control nuclei. TPX2-depleted nuclei assemble nuclear envelopes, nuclear pore complexes, and a lamina, and they perform nuclear-specific functions, including DNA replication. We show that TPX2 interacts with lamina-associated polypeptide 2 (LAP2), a protein known to be required for nuclear assembly in interphase extracts and in vitro. LAP2 localization is disrupted in TPX2-depleted nuclei, suggesting that the interaction between TPX2 and LAP2 is required for postmitotic nuclear reformation.

Nuclear membrane protein LAP2β mediates transcriptional repression alone and together with its binding partner GCL (germ-cell-less)

LAP2β is an integral membrane protein of the nuclear envelope involved in chromatin and nuclear architecture. Using the yeast two-hybrid system, we have cloned a novel LAP2β-binding protein, mGCL, which contains a BTB/POZ domain and is the mouse homologue of the Drosophila germ-cell-less (GCL) protein. In Drosophila embryos, GCL was shown to be essential for germ cell formation and was localized to the nuclear envelope. Here, we show that, in mammalian cells, GCL is co-localized with LAP2β to the nuclear envelope. Nuclear fractionation studies reveal that mGCL acts as a nuclear matrix component and not as an integral protein of the nuclear envelope. Recently, mGCL was found to interact with the DP3α component of the E2F transcription factor. This interaction reduced the transcriptional activity of the E2F-DP heterodimer, probably by anchoring the complex to the nuclear envelope. We demonstrate here that LAP2β is also capable of reducing the transcriptional activity of the E2F-DP complex and that it is more potent than mGCL in doing so. Co-expression of both LAP2β and mGCL with the E2F-DP complex resulted in a reduced transcriptional activity equal to that exerted by the pRb protein.

Thymopentin and splenopentin as immunomodulators. Current status

Splenopentin (SP-5, Arg-Lys-Glu-Val-Tyr) and thymopentin (TP-5, Arg-Lys-Asp-Val-Tyr) are synthetic immunomodulating peptides corresponding to the region 32-34 of a splenic product called splenin (SP) and the thymic hormone thymopoietin (TP), respectively. TP was originally isolated as a 5-kDa (49-amino acids) protein from bovine thymus while studying effects of the thymic extracts on neuromuscular transmission and was subsequently observed to affect T cell differentiation and function. TP I and II are two closely related polypeptides isolated from bovine thymus. A radioimmunoassay for TP revealed a crossreaction with a product found in spleen and lymph node. This product, named splenin, differs from TP only in position 34, aspartic acid for bovine TP and glutamic acid for bovine splenin and it was called TP III as well. Synthetic pentapeptides (TP-5) and (SP-5), reproduce the biological activities of TP and SP, respectively. It is now evident that various forms of TPs were created by proteolytic cleavage of larger proteins during isolation. cDNA clones have been isolated for three alternatively spliced mRNAs that encodes three distinct human T cell TPs. The immunomodulatory properties of TP, SP, TP-5, SP-5 and some of their synthetic analogs reported in the literature have been briefly reviewed.

The characterization and localization of the mouse thymopoietin/lamina-associated polypeptide 2 gene and its alternatively spliced products

Thymopoietins (Tmpos) are a group of ubiquitously expressed nuclear proteins, with sequence homology to lamina-associated polypeptide 2 (LAP2). Here we report the isolation and characterization of seven mouse Tmpo mRNA transcripts named Tmpo alpha, beta, beta', gamma, epsilon, delta, and zeta. The alpha, beta, and gamma Tmpo cDNA clones are the mouse homologs of the previously characterized human alpha, beta, and gamma TMPOs, respectively, whereas Tmpo epsilon, delta, and zeta are novel cDNAs. Additionally, the mouse Tmpo gene was cloned and characterized. It is a single-copy gene organized in 10 exons spanning approximately 22 kb, which encodes all of the described Tmpo cDNA sequences, located in the central region of mouse chromosome 10. The almost identical genomic organization between the human and mouse genes, and the novel alternatively spliced mouse transcripts, led us to reanalyze the human TMPO gene. The human beta-specific domain was found to be encoded by 3 exons designated 6a, 6b, and 6c and not by a single exon as described previously. These findings suggest that there may be more human transcripts than currently recognized. The possible involvement of the new growing family of Tmpo proteins in nuclear architecture and cell cycle control is discussed.

On the mechanism of the modular primer effect

Modular primers are strings of three contiguously annealed unligated oligonucleotides (modules) as short as 5- or 6-mers, selected from a presynthesized library. It was previously found that such strings can prime DNA sequencing reactions specifically, thus eliminating the need for the primer synthesis step in DNA sequencing by primer walking. It has remained largely a mystery why modular primers prime uniquely, while a single module, used alone in the same conditions, often shows alternative priming of comparable strength. In a puzzling way, the single module, even in a large excess over the template, no longer primes at the alternative sites, when modules with which it can form a contiguous string are also present. Here we describe experiments indicating that this phenomenon cannot be explained by cooperative annealing of the modules to the template. Instead, the mechanism seems to involve competition between different primers for the available polymerase. In this competition, the polymerase is preferentially engaged by longer primers, whether modular or conventional, at the expense of shorter primers, even though the latter can otherwise prime with similar or occasionally higher efficiency.

Solid-phase peptide synthesis and biological activity of bovine thymopoietin II (bTP-II)

Bovine thymopoietin (bTP), a 49 amino acid polypeptide, was synthesized using Merrifield's solid-phase peptide synthesis methodology. The polypeptide was purified using anion-exchange chromatography and reversed-phase HPLC and characterized by mass spectrometry and amino acid analysis of the full-length peptide and of products derived from digestion with Staphylococcus aureus V8 protease. The biological activity of the synthesized product was tested in several assay systems. Synthetic bTP was found to induce the expression of Thy 1.2 antigen on T-lymphocytes from athymic mice, in agreement with previous studies on the biological activity of endogenous bTP. Biological activity at skeletal muscle and neuronal nicotinic acetylcholine receptor sites, as reported by others for bTP, could not be confirmed in our studies. The absence of biological activity at nicotinic receptor sites may be related to the results of a recent report demonstrating the presence of a cobratoxin-like molecule in preparations of natural bTP. These data indicate that synthetic peptides have an important role for the evaluation of the specificity of the biological activity of polypeptides.

Three distinct human thymopoietins are derived from alternatively spliced mRNAs

Thymopoietin (TP) was originally isolated as a 5-kDa 49-aa protein from bovine thymus in studies of the effects of thymic extracts on neuromuscular transmission and was subsequently observed to affect T-cell differentiation and function. We now report the isolation of cDNA clones for three alternatively spliced mRNAs that encode three distinct human T-cell TPs. Proteins encoded by these mRNAs, which we have named TP alpha (75 kDa), TP beta (51 kDa), and TP gamma (39 kDa), contain identical N-terminal regions, including sequences nearly identical to that of the originally isolated 49-aa protein, but divergent C-terminal regions. TP mRNAs are expressed in many tissues, most abundantly in adult thymus and fetal liver of the tissues so far examined. Distinct structural domains and functional motifs in TPs alpha, beta, and gamma suggest that the proteins have unique functions and may be directed to distinct subcellular compartments.