The effects of purifying selection on patterns of genetic differentiation between Drosophila melanogaster populations.

Using the data provided by the Drosophila Population Genomics Project, we investigate factors that affect the genetic differentiation between Rwandan and French populations of D. melanogaster. By examining within-population polymorphisms, we show that sites in long introns (especially those >2000 bp) have significantly lower π (nucleotide diversity) and more low-frequency variants (as measured by Tajima's D, minor allele frequencies, and prevalence of variants that are private to one of the two populations) than short introns, suggesting a positive relationship between intron length and selective constraint. A similar analysis of protein-coding polymorphisms shows that 0-fold (degenerate) sites in more conserved genes are under stronger purifying selection than those in less conserved genes. There is limited evidence that selection on codon bias has an effect on differentiation (as measured by FST) at 4-fold (degenerate) sites, and 4-fold sites and sites in 8-30 bp of short introns ⩽65 bp have comparable FST values. Consistent with the expected effect of purifying selection, sites in long introns and 0-fold sites in conserved genes are less differentiated than those in short introns and less conserved genes, respectively. Genes in non-crossover regions (for example, the fourth chromosome) have very high FST values at both 0-fold and 4-fold degenerate sites, which is probably because of the large reduction in within-population diversity caused by tight linkage between many selected sites. Our analyses also reveal subtle statistical properties of FST, which arise when information from multiple single nucleotide polymorphisms is combined and can lead to the masking of important signals of selection.

Glycoinositol phospholipid anchor and protein C-terminus of bovine erythrocyte acetylcholinesterase: analysis by mass spectrometry and by protein and DNA sequencing.

Purified bovine erythrocyte acetylcholinesterase (AChE) was radiomethylated on its amine groups and incubated with bacterial phosphatidylinositol-specific phospholipase C to remove the lipid portion of the AChE glycoinositol phospholipid (GPI) anchor, and a C-terminal tryptic fragment that contained the residual GPI glycan was isolated by HPLC. Analysis by electrospray-ionization mass spectrometry revealed a parent ion of m/z 3798. The fragmentation patterns produced by collision-induced dissociation mass spectrometry of the +4 and +5 states of the parent ion indicated a 23-amino acid peptide in amide linkage to ethanolamine-P04-Hex-Hex-Hex(PO4-ethanolamine)(HexNAc)-Hex N(Me)2-inositol phosphate. The glycan structure is completely consistent with that obtained previously for the GPI anchor of human erythrocyte AChE except for the addition of the HexNAc substituent. A nearly complete peptide sequence was deduced from the fragmentation patterns, although four assignments were based only on single fragments of very low abundance. To resolve this uncertainty, a segment of bovine genomic DNA corresponding to the C-terminal AChE sequence was amplified by PCR. DNA sequencing established the 23-amino acid peptide sequence to be FLPKLLSATASEAPCTCSGPAHG, in agreement with the MS data and consistent with results from Edman protein sequencing. Dimerization of AChE polypeptides is mediated by intersubunit disulphide bonding in this C-terminal segment, but the bovine AChE contained two cysteine residues in a ...CTC... motif, in contrast with human AChE which contains only a single cysteine in this segment. Although bovine AChE contained no free thiol groups reactive with iodo[14C]acetamide, partial reduction and alkylation with iodo[14C]acetamide revealed that conversion into monomers occurred with an overall incorporation of only one alkyl group per monomer. An identical level of alkylation was observed when dimeric human AChE was converted into monomers by partial reduction. The question of whether the bovine AChE contains one or two intersubunit disulphide linkages is considered.

Migratory behavior of PC12 cells transplanted into neonatal rat brain.

PC12 rat pheochromocytoma cells form tumors when transplanted into the forebrains of 1-4-day-old neonatal rats; thereafter, the incidence of tumor formation declines rapidly with increasing recipient age. The fate of PC12 cells transplanted into the forebrains of older neonates is thus not well defined. To examine the interactions of PC12 cells with this older neural environment, we transplanted [3H]thymidine-labeled PC12 cells into the brains of 5-day-old rats. In the brains of animals sacrificed 5 days after transplantation, clusters of labeled cells were found in and around the lateral and third ventricles. By 11 days after transplantation, single labeled cells were found to migrate into the hippocampus and the nearby cerebral cortex. Occasional invasion of the ventral hypothalamus from the third ventricle was also observed. Cells were rarely found to cross the midline or to invade the thalamus or the midbrain. The same pattern of labeling was found in the brains of animals sacrificed at 16 days after inoculation, suggesting that migration was completed by that time. No tumors were detectable, despite the implantation of cells in and around the ventricles. Control injections of [3H]thymidine alone or of [3H]thymidine-labeled astrocytes showed no labeling above background. These results suggest that PC12 cells migrate after inoculation into the brains of older neonatal rats. Additionally, this migration may be regionally constrained and dictated by the specific local trophic environment.

Primary structure of gonadotropin-releasing hormone from the brain of a holocephalan (ratfish: Hydrolagus colliei).

Gonadotropin-releasing hormone (GnRH) in the ratfish brain has been isolated and purified using reverse-phase high performance liquid chromatography. Amino acid composition and sequence analysis indicate that the primary structure is pGlu-His-Trp-Ser-His-Gly-Trp-Tyr-Pro-Gly-NH2. The presence of the amino terminal pyroglutamic acid has been confirmed by degradation studies with pyroglutamyl aminopeptidase. The amidated carboxy terminus and molecular weight were confirmed using mass spectrometry. Moreover, sequence comparison and coelution studies with one of the synthetic forms of GnRH (chicken GnRH II) indicate that the ratfish and chicken GnRH II molecules are identical. This represents the first sequence data of a GnRH molecule from a cartilaginous fish (class: Chondrichthyes). It is argued that the ratfish GnRH molecule has been retained for over 400 million years of evolution and is expressed in most vertebrate classes.

Motivation of plateletpheresis donors.

Twenty randomly chosen voluntary plateletpheresis donors were interviewed in depth. Information on their family histories, past histories, present psychosocial adjustment, and history of blood donation was elicited. Most donors had a high level of commitment and drive to achieve, frequently related to low self-image dating from childhood. The act of platelet donation had several important meanings for the subjects. It improved their self-esteem, making them feel more worthy and responsible persons. It provided them with an opportunity to establish relationships with others. The data obtained in this survey suggest that the altruistic behavior of the voluntary donors should be seen both as an act of giving and also one of receiving emotional gratification which fulfills one's important psychological needs. Utilization of these data in recruitment of plateletpheresis donors is suggested.