Maternal messenger RNA distribution in silkmoth eggs. I. Clone Ec4B is associated with the cortical cytoskeleton.

We have constructed a cDNA library from mature egg RNA of the silkmoth, Hyalophora cecropia. Differential screening of the library using cDNA made against mRNAs from the yolky cytoplasm (soluble fraction) and the cortical cytoplasm (cytoskeletal-associated or cortical fraction) resulted in several clones that hybridized to a higher degree to the cDNA from the cytoskeletal-associated fraction. We selected and analyzed the clone giving the strongest signal (designated Ec4b) for its distribution in situ and found that it bound to mRNAs in the nurse cell cytoplasm, in the cortex and in the follicle cells of oocytes. Hybridization of the insert from Ec4b to both detergent-soluble and -insoluble (cortical) RNA on dot blots further supported the observation that the mRNA corresponding to Ec4b was enriched in this cytoskeletal fraction. The mRNA for Ec4b was approximately 500 bases long and the gene seems to be a member of a large multigene family in the H. cecropia genome. Analyses of the nucleotide and amino acid sequences reveal similarity to lepidopteran chorion genes and a lesser but convincing similarity to vertebrate cytokeratins. The filter and in situ hybridization data point to the association of specific messenger RNAs with the cortical cytoskeleton of silkmoth oocytes. Aspects of the structure of the protein encoded by this mRNA suggest that it is a structural component necessary for formation of the cellular blastoderm of the embryo. The association of this maternal mRNA with the cortical cytoskeleton presents the interesting possibility that mRNA bound to the cytoskeleton may be capable of participating in the synthesis of new cytoskeleton or related structures during blastoderm formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation of rat major histocompatibility genes expressed in pancreatic beta-cells.

The probable role of cell surface antigens in the development of juvenile diabetes necessitates a detailed study of the proteins expressed on the surface of pancreatic beta-cells. A gene library composed of genes expressed in beta-cells was constructed to provide a source of low abundance genes from those cells. Initial studies with this library have led to the isolation of three genes which share nucleotide and amino acid sequence homology with mouse and human class I major histocompatibility antigens.

Estrogen regulates the number of RNA polymerase II molecules in rooster liver.

Administration of estrogen to roosters causes an increase in the activities of DNA-dependent RNA polymerases I and II in nuclei isolated from liver. In an effort to determine the cause of this increased transcriptional activity, we have examined the activity of RNA polymerase II that we have solubilized from nuclei of normal, estrogen-stimulated, and estrogen-withdrawn roosters. In addition, we have measured the actual numbers of RNA polymerase II molecules per nuclear equivalent of DNA in livers of roosters in each estrogenic state by the technique of [3H]amanitin-binding. The administration of estrogen is attended by a 2-fold increase in enzymatic activity of solubilized RNA polymerase II per liver nucleus within 24 h. In addition, there is a 2-fold increase in the number of RNA polymerase II molecules per nucleus in the livers of these animals after the administration of estrogen. During withdrawal from estrogen for 14 days, the activities of RNA polymerases I and II in isolated nuclei and the activity of solubilized RNA polymerase II return to the unstimulated levels. Moreover, the [3H]amanitin-binding capacity of nuclear extracts from the livers of roosters in various stages of hormonal stimulation closely mimics the RNA polymerase II activity of the same extracts. These observations indicate that estrogen exerts a rigid control over the population of RNA polymerase II molecules in avian liver.

Reprogramming in the absence of DNA synthesis in Galleria larval epidermis.

Larval epidermal cells from a day-1 penultimate instar Galleria larva on implantation into day-5 last instar larva metamorphose and deposit a pupal cuticle at the same time as the host pupates. DNA synthesis in the implanted larval cell was monitored with 3-H-thymidine. Various regimens of 3-H-thymidine application were used and under no conditions did the larval cells incorporate label during the period from implantation to deposition of pupal cuticle. This suggests that a wax moth larval ectoderm cell can reprogram its genome to secrete a pupal cuticle without a precedent cell division.