Genome-wide CRISPR Screens Reveal Host Factors Critical for SARS-CoV-2 Infection

1. Download : Download high-res image (212KB)
2. Download : Download full-size image

     

ADAPTATIONS TO CLIFF-NESTING IN SOME ARCTIC GULLS (LARUS)

Various aspects of the breeding of three gulls, Larus thayeri, glaucoides and hyperboreus, which nested in colonies both on cliff ledges and on level ground in the eastern Canadian Arctic, were compared with those of the ground-nesting L. argentatus and the cliff-nesting Rissa tridactyla. As the result of adaptation to cliff ledge nesting, many aspects of the breeding biology of R. tridactyla were strikingly different from those of the ground-nesting European L. argentatus, but the behaviour of L. thayeri, glaucoides and hyperboreus clearly spanned these differences. Cliff-nesting individuals of thayeri and glaucoides were most like Rissa; ground-nesting individuals of these species were most like argentatus. L. thayeri was more like Rissa than was glaucoides. With but few exceptions, both cliff- and ground-nesting individuals of hyperboreus were most like argentatus. The factors responsible for the intra-specific differences between cliff- and ground-nesters of thayeri and glaucoides are not clear. Limited gene exchange between cliff and ground colonies occurs. Because of physical features of the nest, first-laid eggs were more liable to fall from ledges than second or third eggs. L. thayeri and glaucoides have evolved separate mechanisms to cope with this problem. Egg shape was multimodal in thayeri and glaucoides. Long pyriform eggs were less liable to fall from ledges than eggs of other shapes. L. thayeri laid more long pyriform eggs as first eggs than did glaucoides. L. thayeri lost fewer eggs than did glaucoides, but glaucoides replaced all lost eggs while thayeri did not. Delayed follicular atresia provided glaucoides with insurance of egg replacement. In thayeri, accessory follicles were reabsorbed after the first egg was laid; in argentatus, after the second egg, and in glaucoides after the third egg. At the approach of a predator, it was advantageous for cliff-dwelling chicks to remain motionless but for ground-dwelling chicks to flee their nests and to hide. Among the cliff-nesters, the “freezing in place” reaction of chicks was best developed in thayeri, to a lesser extent in glaucoides, and least in hyperboreus. Among the ground-nesters, chicks of glaucoides and hyperboreus behaved like those of argentatus and fled their nests when disturbed, but chicks of thayeri froze like their cliff-dwelling siblings. Reciprocal transfers of eggs and chicks between cliff and ground colonies indicated that in argentatus, glaucoides and hyperboreus, the factors determining a chick's reaction to disturbance came into play between hatching and the eighth day. In thayeri, the reaction appeared to be effectively innate. Chicks of glaucoides showed a greater predisposition to this behaviour than chicks of argentatus after both had received identical experience on cliff ledges. In thayeri, stereotypy of the freezing reaction has probably been a factor limiting the colonisation of areas where cliffs are scarce but predators present. In argentatus, lack of perfection of this behaviour (compared to glaucoides and thayeri) has probably been a factor preventing argentatus from attaining cliff ledges. L. hyperboreus, although nowhere abundant, is a widespread species nesting on level ground and on cliff ledges but lacking the modifications observed in glaucoides and thayeri; this is due to its size and aggressiveness, the fact that it picks nest-sites before glaucoides and thayeri arrive in the colonies, and that on cliffs it chooses the largest and most level ledges.     

Synthesis and biological activity of linear and cyclic enkephalins modified at the Gly3-Phe4 amide bond

As part of our continuing effort to define structure-activity relationships for enkephalin and design enzymatically resistant analogs, we report the synthesis and biological activities of linear and cyclic enkephalin analogs modified at the Gly3-Phe4 amide bond. The partial retro-inverso enkephalin analog Tyr-D-Ala-gGly-(R,S)-mPhe-Leu-NH2 and its cyclic counterpart, Tyr-cyclo[D-A2 bu-gGly-(R,S)-mPhe-Leu-], were synthesized as diastereomeric mixtures using solution methodology. The racemic benzylmalonate allowed the linear analog to be synthesized by fragment coupling at the reversed bond. Cyclization of the second analog was carried out at high concentration, eliminating formation of polymer by the use of an insoluble base. All gem-diaminoalkyl residues were prepared by conversion of peptidyl amides with benzene iodonium bis(trifluoroacetate). Diastereomers of both compounds were separable by reverse phase HPLC but those of the linear compound racemized rapidly under conditions of testing and were therefore tested together. All analogs tested had activities ranging from 6 to 14% of the activity of Leu enkephalin, indicating that the Gly3-Phe4 amide bond is important, though not crucial, for receptor binding.     

Über eine besondere Art von Laubfall bei einigen immergrünen Holzgewächsen

Ohne Zusammenfassung     

DNA sequence homology between attB-related sites of Corynebacterium diphtheriae, Corynebacterium ulcerans, Corynebacterium glutamicum, and the attP side of γ-Cornephage

Chromosomal restriction fragments of Corynebacterium ulcerans and C. diphtheriae, containing an integration site for corynephages of the beta family, show homology on Southern blots. Homologous DNA in also found in the soil isolate C. glutamicum, although this strain is not susceptible to beta-corynephages. Three of these DNA fragments, one for each bacterial strain, and a fragment of gamma-corynephage DNA previously shown to contain the phage integration site, were cloned and sequenced. Alignment of the 3 bacterial sequences shows a very high degree of homology in a stretch of ca 120 nucleotides, whereas the rest of the sequences is generally non-homologous. Within this common bacterial portion, a segment of ca. 96 nucleotides (core sequence) is also highly homologous to the phage sequence. The first half (ca. 50 bp) of the core sequence is identical in all aligned sequences whereas the second half, which is largely occupied by a stem-and-loop structure, contains point mutations peculiar to each clone. The described sequences are likely to be involved in phage integration/excision processes.     

The association between spontaneous pyelonephritis and maturity-onset diabetes mellitus in male MM mice

Blood glucose and glucose tolerance tests demonstrated that many male MM mice are diabetic. Serial urine sampling showed that the diabetes occurred only in mature MM males and consisted of a single self-limiting episode. Histological examination of the pancreas, together with measurements of body weight, glycosylated haemoglobin and plasma insulin, revealed that the diabetes was of the maturity-onset insulin-resistant type. Bacteriological examination of the urine samples showed that urinary tract infection, a known feature of male MM mice, occurred in the diabetics but only after the onset of hyperglucosuria. It was concluded that the high urinary glucose levels of diabetic MM males are of prime importance in the aetiology of the renal infection which occurs rarely in non-diabetic MM males or in other strains in the colony. An infectious aetiology for the diabetes per se was excluded by the existence of diabetes in germfree MM males.     

Allelic Variation within the Emv-15 Locus Defines Genomic Sequences Closely Linked to the agouti Locus on Mouse Chromosome 2

Gene(s) at the agouti locus act within the microenvironment of the hair follicle to switch pigment synthesis in the melanocyte between eumelanin (black or brown pigment) and phaeomelanin (yellow pigment). Many phenotypic variants of this locus have been described. The mechanism(s) of gene action causing such variation in coat-color phenotype is not known. The close linkage of an endogenous ecotropic murine leukemia provirus, Emv-15, to the lethal yellow mutation of the agouti locus provides a means to molecularly access genes at or near the agouti locus. We have identified and used a unique mouse sequence flanking the Emv-15 provirus to define three alleles of the Emv-15 locus. We found a correlation between the presence of specific Emv-15 alleles and the origins of specific agouti locus mutations, confirming close linkage. However, we found some exceptions which suggest that the Emv-15 locus is closely linked to, but genetically separable from, the agouti locus.