3' RACE: skewed ratio of specific to general PCR primers improves yield and specificity

Endo/exocytosis in the pollen tube apex is differentially regulated by Ca2+ and GTPases

Pollen tube growth relies on an extremely fast delivery of new membrane and wall material to the apical region where growth takes place. Despite the obvious meaning of this fact, the mechanisms that control this process remain very much unknown. It has previously been shown that apical growth is regulated by cytosolic free calcium ([Ca(2+)](c)) so it was decided to test how changes in [Ca(2+)](c) affect endo/exocytosis in pollen tube growth and reorientation. The endo/exocytosis was assayed in living cells using confocal imaging of FM 1-43. It was found that growing pollen tubes exhibited a higher endo/exocytosis activity in the apical region whereas in non-growing cells FM 1-43 is uniformly distributed. During pollen tube reorientation, a spatial redistribution of exocytotic activity was observed with the highest fluorescence in the side to which the cell will bend. Localized increases in [Ca(2+)](c) induced by photolysis of caged Ca(2+) increased exocytosis. In order to find if [Ca(2+)](c) changes were modulating endo/exocytosis directly or through a signalling cascade, tests were conducted to find how changes in GTP levels and GTPase activity (primary regulators of the secretory pathway) affect the apical [Ca(2+)](c) gradient and endo/exocytosis. It was found that increases in GTP levels could promote exocytosis (and growth). Interestingly, the increase in [GTP] did not significantly affect [Ca(2+)](c) distribution, thus suggesting that the apical endo/exocytosis is regulated in a concerted but differentiated manner by the Ca(2+) gradient and the activity of GTPases. Rop GTPases are likely candidates to mediate the Ca(2+)/GTP cross-talk as shown by knock-down experiments in growing pollen tubes.

Determination of the cDNA sequence and mRNA expression of interleukin-1 receptor antagonist in horses

OBJECTIVE

To determine the complementary DNA (cDNA) sequence of interleukin-1 receptor antagonist (IL-1ra) in horses and compare messenger RNA (mRNA) expression of IL-1ra among horses of various breeds.

SAMPLE POPULATION

Blood samples from neonatal and adult horses examined for a variety of diseases.

PROCEDURE

A polymerase chain reaction procedure was used to amplify a 220 base pair (bp) portion of the genomic DNA. The upstream and downstream regions of the cDNA sequence were determined by means of 5' and 3' rapid amplification of cDNA ends (RACE) procedures. Northern blot hybridization was used to examine steady-state mRNA expression of IL-1ra.

RESULTS

The consensus sequence of the cDNA obtained with the 5'-RACE procedure and the sequence for the 220 bp portion of the genomic DNA represented the putative sequence for secreted IL-1ra. The predicted secreted IL-1ra amino acid sequence contained 176 residues with an in-frame stop codon; the N-terminal 25 amino acid residues resembled the signal peptide reported for human secreted IL-1ra. An approximately 1.3 kilobase pair (kb) band that represented a portion of the 3' end of the coding region and the 3' untranslated region was obtained by use of the 3' -RACE procedure. Northern blot hybridization detected a 1.6 kb transcript in blood RNA from adult Arabian, Belgian, Thoroughbred, and Standardbred horses.

CONCLUSIONS

Results suggest that the DNA for equine secreted IL-1ra has a short (29 bp) 5' untranslated region, a 534 bp coding region, and a long (approximately 1,080 bp) untranslated region.

Molecular cloning and functional expression of human ST6GalNAc II. Molecular expression in various human cultured cells

A cDNA clone encoding a human Galbeta1-3GalNAc alpha2, 6-sialyltransferase (designated hST6GalNAc II) was identified employing the PCR with degenerated primers to the sialylmotifs, followed by BLAST analysis of databanks. This sialyltransferase sequence is similar to that of previously cloned ST6GalNAc II (chicken and mouse) and shows the sialylmotifs that are present in all eukaryotic members of the sialyltransferase gene family. The predicted amino acid sequence encodes a putative type II transmembrane protein as found for other eukaryotic sialyltransferases and shows significant similarity to chicken (56. 8% identity) and mouse (74.6% identity) enzymes. Expression of a secreted form of hST6GalNAc II in COS-7 cells showed that the gene product had Galbeta1-3GalNAc (sialyl to GalNAc) alpha2, 6-sialyltransferase activity. In vitro analysis of substrate specificity revealed that the enzyme required a peptide aglycone fraction to be active and used both Galbeta1-3GalNAc and Neu5Acalpha2-3Galbeta1-3GalNAc as acceptor substrates. Northern analysis revealed a restricted expression pattern of two hST6GalNAc II transcripts, a 2.0 kb mRNA found mainly in skeletal muscle, heart and kidney and a 1.8 kb mRNA found in placenta, lung and leukocytes. No transcriptional expression was detected in brain, thymus or spleen. Transcriptional expression of the ST6GalNAc II gene was followed in various human cell lines and found to be expressed in almost all cell types with notable exceptions for several myeloid and lymphoid cell lines.

Tissue-specific N-terminal isoforms from overlapping alternate promoters of the human AE2 anion exchanger gene

Previously, we isolated the human AE2 (SLC4A2) gene, a member of the sodium-independent anion exchanger family. Rat ortholog of this gene was reported to drive alternative transcription yielding N-terminal variants of the AE2a message. We thus analyzed the human AE2 gene in this regard. Using HepG2 cells, two alternative first exons, each splicing to exon 3 in alternative transcripts, were found to be transcribed from overlapping sequences of intron 2. Exon 1b(1) corresponds to the rat variant "b" and encodes three initial residues (MTQ) in AE2b(1) isoform that replace the first 17 amino acids of AE2a protein, while the novel exon 1b(2) encodes eight initial residues (MDFLLRPQ) in AE2b(2) isoform. The relative abundance of AE2b(1) and AE2b(2) mRNAs was about 10% of AE2a mRNA each. Alternate promoter sequences have multiple potential binding motifs for liver-enriched factors, and dual-luciferase assays indicated that they possess the ability for driving transcription in transiently transfected HepG2 cells. Tissue survey showed that expression of human AE2b(1) and AE2b(2) transcripts is restricted to liver and kidney, while AE2a mRNA was encountered in all examined tissues. Our findings reveal a characteristic tissue-specific expression of two N-terminal variants of human AE2 from overlapping sequences within intron 2, one of which is a novel isoform.

Identification of a novel LIM domain gene, LMCD1, and chromosomal localization in human and mouse

A new human LIM domain gene LMCD1 was identified from RT-PCR products, and partial sequencing of two expressed sequence tag clones flanking the assembled cDNA contig revealed a 1743-bp full-length cDNA with 1098-bp open reading frame. The coding sequence of the putative protein is 57.6% identical to murine testin 1 gene (Tes1), whereas the predicted 365-amino-acid protein is 49.5% identical to the mouse Tes1 protein. The predicted LMCD1 protein contains a novel cysteine-rich domain residing in the amino-terminal region and two LIM domains with regular spacing in the carboxy-terminal region. Northern blot analysis indicated expression of the 1.7-kb transcript in many tissues, with highest abundance in skeletal muscle. Radiation hybrid mapping localized human LMCD1 to the telomeric region of chromosome 3p, and genetic mapping assigned the mouse Lmcd1 locus to the central region of chromosome 6.