Fetal stimulation of maternal immunoglobulin production in mice

Within 12-24 h of parturition in mice, there was a dramatic increase in the number of immunoglobulin secreting cells in the paraaortic lymph nodes (PALN) draining the pregnant uterus. Compared with stimulation with lipopolysaccharide the ratio of IgG:IgM forming cells was very high in PALN draining a pregnant uterus. The response was eliminated when fetectomy (ablating the embryo but leaving the placenta intact) was carried out on the 12th day of pregnancy. With unilateral fetectomy the uterine horn with intact fetal/placental units can be used as a positive control since lymphoid drainage is laterally confined. Neither healthy (gross and histological criteria) nor partly necrotic placentae stimulated Ig secreting cells in the PALN. The placentae of bilaterally fetectomized females were delivered apparently normally and at about the same time as normal (control) fetuses. Injection of prostaglandin E-2 or F-2 alpha into the tail base led to the appearance of Ig-forming cells in the PALN of normal (virgin) female mice. Indomethacin fed to the pregnant female greatly reduced the numbers of these cells in the PALN. We conclude that the observed local stimulation of maternal Ig production by the fetus may be involved in the transplacental transfer of Ig from mother to fetus.     

Localization of sequences regulating ancestral and acquired sites of esterase6 activity in Drosophila melanogaster

We have broadly defined the DNA regions regulating esterase6 activity in several life stages and tissue types of D. melanogaster using P- element-mediated transformation of constructs that contain the esterase6 coding region and deletions or substitutions in 5' or 3' flanking DNA. Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and the primary sequences regulating its activity lie between -171 and -25 bp relative to the translation initiation site: deletion of these sequences decrease activity approximately 20-fold. Hemolymph activity is also modulated by four other DNA regions, three of which lie 5' and one of which lies 3' of the coding region. Of these, two have positive and two have negative effects, each of approximately twofold. Esterase6 activity is present also in two male reproductive tract tissues; the ejaculatory bulb, which is another ancestral activity site, and the ejaculatory duct, which is a recently acquired site within the melanogaster species subgroup. Activities in these tissues are at least in part independently regulated: activity in the ejaculatory bulb is conferred by sequences between -273 and -172 bp (threefold decrease when deleted), while activity in the ejaculatory duct is conferred by more distal sequences between -844 and -614 bp (fourfold decrease when deleted). The reproductive tract activity is further modulated by two additional DNA regions, one in 5' DNA (-613 to -284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to +2731 bp; threefold decrease when deleted) that probably overlaps the adjacent esteraseP gene. Collating these data with previous studies suggests that expression of EST6 in the ancestral sites is mainly regulated by conserved proximal sequences while more variable distal sequences regulate expression in the acquired ejaculatory duct site.      

Successful in vitro and in vivo development of in vitro fertilized two- to four-cell cat embryos following cryopreservation, culture and transfer

In vitro and in vivo survival of in vitro-derived 2- to 4-cell cat embryos following cryopreservation was examined. Prefreeze 1- vs 2-step cryoprotectant exposure (Experiment 1) and warming method (Experiment 2) on zona pellucida damage and development in vitro were compared. To determine viability in vivo, frozen/thawed embryos were cultured in vitro to the morula/early blastocyst stage and transferred to synchronous recipients (Experiment 3). At 24 to 26 h after IVF, embryos were cryopreserved in 1.4 M propanediol (Pr) + 0.125 M sucrose (Su) by cooling at 0.3 degrees C/min from -6 degrees C to -30 degrees C and storing in liquid nitrogen. Autologous embryos were cultured in vitro for 7 d. After warming for 5 sec in air and 10 sec at 37 degrees C in water (Experiments 1 to 3), or at room temperature air (22 degrees C; Experiment 2), the cryoprotectant was removed and embryos were cultured in vitro for 6 d (Experiments 1 and 2). Development was assessed after staining by counting cell numbers/embryo and determining the percentages at the 2- to 4-cell (nonsurvivor), pre (5 to 15), early (16 to 32), mid (33 to 50), late (>50) morula or blastocyst stages. Post-thaw development to late morula/blastocyst after 1-step exposure (68%, 15 min Pr + Su) was higher (P< 0.05) than that after 2-step exposure (36%, 15 min Pr and 15 min Pr + Su). Both warming methods produced similar percentages of embryos with damaged zonae (13 to 15%) and equivalent development to morula/blastocyst (64 to 69%). Development in vitro to early morula/blastocyst of frozen embryos with intact zonae was similar to that of nonfrozen embryos. Following cryopreservation, most 2- to 4-cell cat embryos retained their capability for in vitro development to morula/blastocyst, and in vivo viability was demonstrated by the birth of 3 live kittens to 2 of 4 recipients following the transfer of 58 embryos.     

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Feedback by early and late primary antisera on the primary and secondary adoptive immune responses of mice to burro erythrocytes

Experiments on antibody feedback inhibition of the immune response have confirmed that control is more effective against a primary response than against a secondary response. The cells producing antibodies in primary and secondary responses are different both in terms of number of IgFC and amount of antibody produced by individual IgFC (plaque size). Late primary anti-burro RBC sera (greater than 200 days), despite low titers, are, on a volume for volume basis, feedback inhibitors at least as good as early (8-12 days) primary antisera on primary responses but are more effective in suppressing secondary responses (B memory cells). Late primary antisera, due to the process of affinity maturation, have a high affinity for antigen. The suppressive effect of early and late antisera is equally removable by absorption with burro erythrocytes: a result which it is thought, decreases the likelihood of feedback by anti-idiotype being involved in the observed suppression. It is suggested that feedback antibody acts (a) in competition with receptors, inter alia removing antigen into immunologically irrelevant pathways, (b) by a process involving the linking of antigen to Fc receptors, and (c) as a blocking antibody coating B cells (Bm) or APC which are already binding epitopes, thus preventing their cooperation with specific helper or other accessory cells.     

Meiotic Crossover Control by Concerted Action of Rad51-Dmc1 in Homolog Template Bias and Robust Homeostatic Regulation

During meiosis, repair of programmed DNA double-strand breaks (DSBs) by recombination promotes pairing of homologous chromosomes and their connection by crossovers. Two DNA strand-exchange proteins, Rad51 and Dmc1, are required for meiotic recombination in many organisms. Studies in budding yeast imply that Rad51 acts to regulate Dmc1''s strand exchange activity, while its own exchange activity is inhibited. However, in a dmc1 mutant, elimination of inhibitory factor, Hed1, activates Rad51''s strand exchange activity and results in high levels of recombination without participation of Dmc1. Here we show that Rad51-mediated meiotic recombination is not subject to regulatory processes associated with high-fidelity chromosome segregation. These include homolog bias, a process that directs strand exchange between homologs rather than sister chromatids. Furthermore, activation of Rad51 does not effectively substitute for Dmc1''s chromosome pairing activity, nor does it ensure formation of the obligate crossovers required for accurate homolog segregation. We further show that Dmc1''s dominance in promoting strand exchange between homologs involves repression of Rad51''s strand-exchange activity. This function of Dmc1 is independent of Hed1, but requires the meiotic kinase, Mek1. Hed1 makes a relatively minor contribution to homolog bias, but nonetheless this is important for normal morphogenesis of synaptonemal complexes and efficient crossing-over especially when DSB numbers are decreased. Super-resolution microscopy shows that Dmc1 also acts to organize discrete complexes of a Mek1 partner protein, Red1, into clusters along lateral elements of synaptonemal complexes; this activity may also contribute to homolog bias. Finally, we show that when interhomolog bias is defective, recombination is buffered by two feedback processes, one that increases the fraction of events that yields crossovers, and a second that we propose involves additional DSB formation in response to defective homolog interactions. Thus, robust crossover homeostasis is conferred by integrated regulation at initiation, strand-exchange and maturation steps of meiotic recombination.     

The role of snail aestivation in transmission of schistosomiasis in changing climatic conditions

Schistosomiasis vector snails are subjected to extreme seasonal changes, particularly in ephemeral rivers and lentic waterbodies. In the tropics, aestivation is one of the adaptive strategies for survival and is used by snails in times of extremely high temperatures and desiccation. Aestivation therefore plays an important role in maintaining the transmission of schistosomiasis. This review assesses the possible impacts of climate change on the temporal and spatial distribution of schistosomiasis-transmitting snails with special emphasis on aestivation, and discusses the effect of schistosome infection on aestivation ability. The impacts of parasite development on snails, as well as physiological changes, are discussed with reference to schistosomiasis transmission. This review shows that schistosome-infected snails have lower survival rates during aestivation, and that those that survive manage to get rid of the infection. In general, snail aestivation ability is poor and survival chances diminish with time. Longer dry periods result in fewer, as well as uninfected, snails. However, the ability of the surviving snails to repopulate the habitats is high.