An improved 5' RACE technique facilitates the detection of multiple transcript initiation sites

The Human Achaete Scute Homolog 2 gene contains two promotors, generating overlapping transcripts and encoding two proteins with different nuclear localization

Placental development involves control by the basic helix-loop-helix transcription factor Mash2. Transcript analysis of the Human Achaete Scute Homolog 2 (HASH2) mRNA revealed the presence of two overlapping transcripts in first trimester placentae. The two transcripts (2.6 and 1.5 kb) are generated by two promotors which are separated by 1.1 kb, generating transcripts 1 and 2, respectively. Surprisingly, in transcript 1 which shows a broad expression, a second potential coding region, tentatively called Human Achaete Scute Associated Protein (HASAP) was present. Transcript 2 contains the HASH2 encoding region only. Analysis of protein expression from both transcripts by transfection studies with eGFP fusion proteins, revealed that both coding regions are translated from their endogenous translation initiation site and showed that both proteins are transported to the nucleus. HASH2 is distributed throughout the nucleus but the HASAP protein is transported into nuclear compartments, the nucleoli. In addition, the HASAP protein lacks the bHLH domain and bears no homology to known proteins. Moreover, allele-specific RT-PCR showed the human gene not to be subject to imprinting, possibly reflecting the biallelic expression of one of both transcripts. Our data indicate a species-specific difference between mouse and human expression of the Achaete Scute Homolog 2 and suggests a dual function of the human homologue.

Specific expression of glucose-6-phosphate dehydrogenase (G6PDH) gene by salt stress in wheat (Triticum aestivum L.)

We isolated three kinds of full-length cDNA clones for glucose-6-phosphate dehydrogenase (G6PDH) from wheat. They showed over 80% sequence homology with potato and alfalfa at the amino acid level, suggesting that the genes are highly conserved in angiosperms. The lack of a plastidic signal sequence, as well as a higher transcript accumulation level in roots than leaves, suggested that the wheat cDNA sequences encode the cytosolic isoform of the enzyme. Genomic Southern analysis revealed that the isoform is encoded by a few copies of the gene in the wheat genome. Southern analysis of nullisomic-tetrasomic lines suggested that at least one gene is located on chromosome 2B. The G6PDH transcript started to accumulate in the roots after 2 h of 0.15 M NaCl treatment, reaching its maximal level after 12 h of exposure. The G6PDH gene did not respond to either mannitol or abscisic acid (ABA) treatment. The NaCl-specific early response of the G6PDH gene is discussed in relation to the putative role of the enzyme in the salt stress response in plants.

Maternal expression and early zygotic regulation of the Hox3/zen gene in the grasshopper Schistocerca gregaria

In insects, a key step in the early patterning of the egg is to distinguish the primordium of the embryo proper from those regions that will form extra-embryonic membranes. In Drosophila, where these processes are well understood, the structure of the extra-embryonic membranes is highly derived. The distinct amnion and serosa typical of lower insects is replaced by a single, fused, and much reduced membrane, the amnioserosa, which never secretes an embryonic cuticle. We have used the Zen gene as a marker to study the formation of the extra-embryonic membranes, and other aspects of early embryonic patterning, in the grasshopper Schistocerca gregaria (African Plague Locust). Zen genes are derived from Hox genes, but in Drosophila they appear to have lost any role in patterning the A/P axis of the embryo; instead, they are involved in D/V patterning and the specification of the extra-embryonic membranes. We show that the Schistocerca zen gene is expressed during embryogenesis in three distinct phases. The first of these is during cleavage, when Sgzen is transiently expressed in all energids that reach the cell surface. The second phase of expression initiates in a ring of "necklace cells" that surround the forming embryo, and demarcate the boundary between the amnion and serosa. This leads to expression throughout the serosa. The final phase of expression is in the amnion, after this has separated from the serosa. This complex pattern implies that the role of Sgzen in Schistocerca is not limited solely to the specification of cell identity in the extra-embryonic membranes. We also report that the Schistocerca zen gene is expressed maternally, unlike its Drosophila and Tribolium counterparts. A distinct maternal transcript, and maternal Zen protein, accumulate in the developing oocyte from early post-meiotic stages. They remain uniformly distributed in the oocyte cytoplasm until late vitellogenic stages, when the protein and RNA become somewhat concentrated at the egg cortex and in the posterior polar cap of the oocyte, probably by passive exclusion from the yolk. The cytoplasmic localization of Sgzen protein in the oocyte, and at some stages during embryogenesis, implies that nuclear exclusion of this transcription factor is specifically controlled.