Hormonal control of sexual and scent marking behaviors of male gerbils in relation to the sexually dimorphic area of the hypothalamus

The sexual and scent marking behaviors of male gerbils are stimulated by testosterone (T) action in the preoptic area (POA) of the hypothalamus. The sexually dimorphic area (SDA) in the posterior POA, which also responds to T, is implicated in this process. This research studied the sensitivities of mating, marking, and the SDA to T metabolites and other steroids. Experiment 1 focused on mating. Male gerbils were implanted at castration with 2-mm Silastic capsules containing T, dihydrotestosterone (DHT), 19-nortestosterone (19-nor T), estradiol (E), or no hormone and were tested 3-7 weeks later. T, E, and 19-nor T maintained intromissions, but E-treated males rarely ejaculated. Controls and DHT-treated males stopped mounting. Experiment 2 compared the ability of these steroids to reinstate marking and mating using the same dose and a larger one (5 mm). Androstenedione, 19-hydroxytestosterone (19-OHT), and E plus DHT were studied as well. Volumes of the SDA and SDA pars compacta (SDApc) were also measured. Only T, 19-nor T, E, and E + DHT reinstated sexual behavior, but all steroids except 19-OHT stimulated marking. E and DHT synergized to elicit mating. For marking, they were no more effective together than alone. Steroid-treated males had larger SDAs than controls. Moreover, steroids that stimulated sexual activity produced larger SDAs than steroids that did not. SDA size correlated with copulatory rate, but not with copulatory efficiency. SDApc size correlated with copulatory efficiency, but not with copulatory rate. Like copulatory rate and efficiency, sizes of the SDA and SDApc did not correlate with each other.     

Independent control of sexual and scent marking behaviors of male gerbils by cells in or near the medial preoptic area

This research studied the role of the medial preoptic area and adjacent cell populations in androgen control of scent marking and sexual behavior in male gerbils (Meriones unguiculatus). Experiment 1 replicated previous research showing that implants of testosterone propionate in or near the medial preoptic area reinstate marking behavior in castrates. Implant sites near the diagonal band of Broca or in the posterior part of the medial preoptic area, near the anterior hypothalamus, are more effective than other sites. Experiment 2 showed that medial preoptic area lesions permanently impair sexual behavior despite testosterone stimulation. Experiments 2–4 showed that lesions in or near the medial preoptic area can also disrupt scent marking; however, this behavior gradually recovered in many lesioned males, especially if they received testosterone. The data suggest that both scent marking and sexual behavior are controlled by androgens acting on cells in or near the medial preoptic area, but the cell populations involved in these two behaviors are probably not the same.     

Activation and differentiation of sexual behavior and translocation of hypothalamic estrogen receptors in rats by 6α-fluorotestosterone

Androgens classified as nonaromatizable in placental assay systems typically do not mimic testosterone's effects on sexual behavior in rats. 6α-Fluorotestosterone is an exception. To pursue this challenge to the aromatization hypothesis, we compared several behavioral and neuroendocrine effects of 6α-fluorotestosterone propionate (6α-fluoro-TP) with those of testosterone propionate (TP). Even at a very low dose (6.25 μg/100 g/day), 6α-fluoro-TP maintained most aspects of male sexual behavior as well as TP. It was slightly less potent than TP for inhibiting gonadotropin secretion (testicular development) in prepubertal males. Given neonatally, these androgens were equally likely to induce anovulatory sterility. 6α-Fluoro-TP defeminized sexual development in females and neonatally castrated males half as effectively as TP based on lordosis:mount ratios following estrogen and progesterone therapy in adulthood. Neither androgen masculinized sexual behavior. The behavioral effects of 6α-fluoro-TP correspond to its ability to inhibit cell nuclear accumulation of 17β-[³H]estradiol in the hypothalamuspreoptic area. When injected on a schedule like that used to activate male sexual behavior, the two androgens reduced estrogen uptake equally. When injected into adult castrates on a schedule like that used to defeminize sexual development, 6α-fluoro-TP blocked estrogen uptake half as well as TP. 6α-Fluorotestosterone did not alter estrogen uptake when injected simultaneously with 17β-[³H]estradiol. These data suggest that 6α-fluorotestosterone activates male behavior and defeminizes development because it translocates estrogen receptors in the brain, probably via an aromatized metabolite. Hence androgen aromatizability in the placenta may not reflect neural metabolism and cannot predict the behavioral or neuroendocrine effects of androgens.     

Combined observational and experimental data provide limited support for facilitation in lichens

It is increasingly recognized that facilitative interactions can shape communities. One of the mechanisms through which facilitation may operate is when one species facilitates the colonization of another through the exchange of shared symbionts. Lichens are symbiotic associations composed of a mycobiont (lichenised‐fungus) and one or two photobionts (algae or cyanobacteria). Different lichen species may have overlapping specificity for photobionts, creating the possibility that facilitation drives lichen community assembly. To investigate whether facilitation occurs in lichens, we combined an observational study (a) with a manipulative field experiment (b). For (a), we quantified the effect of local patch conditions, facilitation and the size of the surrounding metapopulation on colonizations of an epixylic lichen species (Cladonia botrytes) in an area of managed boreal forest. This was done by twice surveying lichens on 293 stumps, located in stands of three age classes. For (b), we treated unoccupied surfaces of 56 cut stumps with algal mixtures of an Asterochloris photobiont and recorded C. botrytes colonizations over three years. In (a), colonization rates of C. botrytes increased with increasing abundance of other lichen species with specificity for Asterochloris photobionts, consistent with an effect of facilitation. However, in the field experiment (b), colonizations of the focal species did not provide support for facilitation. We conclude that our study provides limited support for facilitation in green‐algal lichens, underscoring the importance of combining observational studies with experiments when studying species interactions.     

Functional reconstitution of bacterial Tat translocation in vitro

The Tat (twin-arginine translocation) pathway is a Sec-independent mechanism for translocating folded preproteins across or into the inner membrane of Escherichia coli. To study Tat translocation, we sought an in vitro translocation assay using purified inner membrane vesicles and in vitro synthesized substrate protein. While membrane vesicles derived from wild-type cells translocate the Sec-dependent substrate proOmpA, translocation of a Tat-dependent substrate, SufI, was not detected. We established that in vivo overexpression of SufI can saturate the Tat translocase, and that simultaneous overexpression of TatA, B and C relieves this SufI saturation. Using membrane vesicles derived from cells overexpressing TatABC, in vitro translocation of SufI was detected. Like translocation in vivo, translocation of SufI in vitro requires TatABC, an intact membrane potential and the twin-arginine targeting motif within the signal peptide of SUFI: In contrast to Sec translocase, we find that Tat translocase does not require ATP. The development of an in vitro translocation assay is a prerequisite for further biochemical investigations of the mechanism of translocation, substrate recognition and translocase structure.     

Interactions among species with contrasting dispersal modes explain distributions for epiphytic lichens

Understanding how the biodiversity response to climate change will be modified at ecological scales, e.g. by species interactions, is a major challenge. Lichen epiphytes – the close interdependent relationship between a heterotrophic fungus and photosynthetic partner (photobiont) – are used here to explore how interaction regimes (between lichen species, and between lichens and their photobionts) explain distribution patterns along spatial climatic gradients. To do this we tested field evidence for the ‘core‐fringe hypothesis’, which proposes a facilitative interaction; sexually‐reproducing and spore‐dispersed lichens with a requirement for resynthesis with a compatible photobiont (Nostoc) are facilitated by the prior establishment of asexual lichens which disperse both the fungus and photobiont together. We used two closely related Nephroma species which differ in their reproductive mode – N. laevigatum (sexual spore‐dispersed) and N. parile (asexual) – and compared their occurrence along a bioclimatic gradient to local habitat factors, including the co‐occurrence of asexual lichens which have shared specificity for compatible Nostoc genotypes. The results showed that: 1) N. laevigatum is significantly more likely to occur on trees that have already been colonised by asexual lichens with shared specificity for Nostoc, supporting the core‐fringe hypothesis, while 2) N. parile is independent of this association (strengthening the core‐fringe hypothesis), with its response to a precipitation gradient modified by microhabitat factors. This positive test for the core‐fringe hypothesis demonstrates how interaction regimes can fundamentally alter expectations under climate change. There is an assumption that spore‐dispersed lichen species could more easily track their suitable bioclimatic space through fragmented habitat, compared to asexual species with larger and heavier propagules. However, the establishment of spore‐dispersed lichen epiphytes into new habitat may be limited by the dispersal rates of asexual species, which act as key facilitators.     

Identification of MarvelD3 as a tight junction-associated transmembrane protein of the occludin family

Background

Protein translocation across the membrane of the Endoplasmic Reticulum (ER) is the first step in the biogenesis of secretory and membrane proteins. Proteins enter the ER by the Sec61 translocon, a proteinaceous channel composed of three subunits, α, β and γ. While it is known that Sec61α forms the actual channel, the function of the other two subunits remains to be characterized.

Results

In the present study we have investigated the function of Sec61β in Drosophila melanogaster. We describe its role in the plasma membrane traffic of Gurken, the ligand for the Epidermal Growth Factor (EGF) receptor in the oocyte. Germline clones of the mutant allele of Sec61β show normal translocation of Gurken into the ER and transport to the Golgi complex, but further traffic to the plasma membrane is impeded. The defect in plasma membrane traffic due to absence of Sec61β is specific for Gurken and is not due to a general trafficking defect.

Conclusion

Based on our study we conclude that Sec61β, which is part of the ER protein translocation channel affects a post-ER step during Gurken trafficking to the plasma membrane. We propose an additional role of Sec61β beyond protein translocation into the ER.