Sertoli cell (SC) androgen receptor (AR) activity is vital for spermatogenesis. We created a unique gain-of-function transgenic (Tg) mouse model to determine the temporal role of SCAR expression in testicular development. The SC-specific rat Abpa promoter directed human Tg AR [Tg SC-specific AR (TgSCAR)] expression, providing strong premature postnatal AR immunolocalized to SC nuclei. Independent Tg lines revealed that TgSCAR dose dependently reduced postnatal and mature testis size (to 60% normal), whereas androgen-dependent mature seminal vesicle weights and serum testosterone levels remained normal. Total SC numbers were reduced in developing and mature TgSCAR testes, despite normal or higher Fshr mRNA and circulating FSH levels. Postnatal TgSCAR testes exhibited elevated levels of AR-regulated Rhox5 and Spinlw1 transcripts, and precocious SC function was demonstrated by early seminiferous tubular lumen formation and up-regulated expression of crucial SC tight-junction (Cldn11 and Tjp1) and phagocytic (Elmo1) transcripts. Early postnatal Amh expression was elevated but declined to normal levels in peripubertal-pubertal TgSCAR vs. control testes, indicating differential age-related regulation featuring AR-independent Amh down-regulation. TgSCAR induced premature postnatal spermatogenic development, shown by increased levels of meiotic (Dmc1 and Spo11) and postmeiotic (Capza3 and Prm1) germ cell transcripts, elevated meiotic-postmeiotic germ:Sertoli cell ratios, and accelerated spermatid development. Meiotic germ:Sertoli cell ratios were further increased in adult TgSCAR mice, indicating predominant SCAR-mediated control of meiotic development. However, postmeiotic germ:Sertoli cell ratios declined below normal. Our unique TgSCAR paradigm reveals that atypical SC-specific temporal AR expression provides a direct molecular mechanism for induction of precocious testicular development, leading to reduced adult testis size and decreased postmeiotic development.
We examined data from 75 infestations of the Mediterranean fruit fly (Medfly) and 286 of the Queensland fruit fly (Qfly) that have occurred in quarantined and normally fly-free zones in Australia from 1974 to 2000. The radius of occurrence of both adult male flies and infested fruit was almost always less than 1 km. The rare cases where there was an isolated occurrence beyond 1 km of an epicentre were most likely due to (and can be treated as) separate introductions. Our analysis shows that effective quarantine radii for suspension of fly-free status should be related to the number of flies trapped around the epicentre and the density of the trap array (if the appropriate code of practice is applied). Most detections of fruit flies involve the trapping of very few flies and 18% of Medfly infestations and 71% of Qfly infestations that are detected are not classified as outbreaks and are left to die out without any treatment. For each species, we have used 3 alternative methods to calculate confidence limits for infestation radii. The upper limits could also serve as quarantine radii. These limits increase with the rate of trapping of male flies and have a theoretical probability of 3/100 000 (i.e. probit 9) of being exceeded. The quarantine radii for most declared outbreaks, when calculated with any of our methods, would be small because the number of flies detected is usually only just above the threshold for such a declaration. If our methods were used for beneficial species or for re-introductions of endangered species, the lower confidence limits could be used to calculate the size of inoculum required for a high probability of initial establishment.
We report the first widespread survey of tephritid fruit flies attempted in a single time period. 1,471 cue lure traps caught 17 species, and extensions to previously recorded geographical ranges were detected for seven of them: Bactrocera tryoni, B. neohumerulis, B. frauenfeldi, B. aeroginosu, Dacus absonifascies, D. aequalis and D. newmani. The traps also unexpectedly caught several B. cacuminatu and also both males and females of Dirioxupornia and Cerutitis capitata. The geographical variation in the relative abundance of B. tryoni and B. neohumeralis in the regjon of their co-occurrence was in substantial agreement with earlier estimates. The regional variation in abundance of B. tryoni in the eastern states was in accordance with the predictions of a published bioclimatic model. Furthermore, the spread of this species (expected from the model) to several locations in the Northern Territory is recorded here for the first time.
Androgen receptor (AR) actions are vital for spermatogenesis. However, in postnatal development male germ cells do not express AR, highlighting its key role in testicular somatic cells. We recently used a Cre-loxP strategy to determine the in vivo requirement of AR DNA-binding in Sertoli cell (SC) function. Transgenic (Tg) mice with Cre expression targeted by SC-specific AMH or Abp promoters were crossed with floxed-Ar (Arflox) mice for Cre-loxP inframe deletion of Ar exon 3, which encodes a zinc finger essential for the DNA-binding domain (DBD). SC-specific mutated ARΔex3 (SCARΔex3) produced infertile AMH.SCARΔex3 and Abp.SCARΔex3 males. Testes from adult homozygous TgCre(+/+) AMH.SCARΔex3 or Abp.SCARΔex3 males were 30% of normal size and exhibited meiotic arrest, whereas testes from hemizygous TgCre(+/–) Abp.SCARΔex3 males were larger (47% normal) with more postmeiotic germ cell development. Despite marked Leydig cell hypertrophy, testicular expression of the adult Leydig marker Hsd3b6 (RT-PCR) and normal intratesticular testosterone levels (LC-MS/MS) in SCARΔex3 males indicated the presence of morphologically distinct but functional adult Leydig cells. SC-specific mutated AR Δex3 was predicted to disrupt classical AR-regulated pathways via loss of direct DNA interaction. Androgen-repressed testicular Ngfr expression (known to be via non-classical AR pathways) was not upregulated in SCARΔex3 testes, suggesting maintenance of a non-classical mechanism independent of AR-DBD. In contrast, SC-specific Rhox5 and Eppin transcription, regulated by divergent or classical androgen-response elements respectively, were both decreased in postnatal SCARΔex3 vs. control testes, demonstrating SC-specific AR function as early as postnatal day 5. However, Rhox5 expression declined dose-dependently, whereas Eppin expression increased, in adult TgCre(+/−) and TgCre(+/+) SCARΔex3 testes, revealing differential temporal control for distinct AR-regulated transcripts. Thus, our SCARΔex3 paradigm displayed dose-dependent TgCre-disruption of meiotic competence and post-meiotic development as well as gene expression, and represents a unique model to selectively differentiate AR-regulated genes.
Male recombination, not normally present in Drosophila melanogaster, can be produced at high rates when target P elements at homologous sites are combined in the presence of transposase protein. We have produced a set of elements by in situ deletion of a particular insertion and have found elements that have deletions stretching into either end. Elements were tested in pairs to see whether they complement each other in their ability to induce recombination. The combination of elements that are deficient for the same end produces very little recombination, but the combination of a right-end and a left-end element can generate recombination values higher than given by two complete P[CaSpeR] elements at homologous sites. This strongly suggests that "hybrid" P elements, containing ends from two different elements, can be recognized by transposase protein. We have also examined genotypes containing a normal and an end-deficient element and found that they yield reasonably high levels of recombination. We interpret the resultant gametes from such genotypes as showing that the majority of events in this genotype derive from the association of complementary ends from the same element, whereas the complementary ends from elements in trans associate in only a minority of cases.
The population structure of a tephritid pest species, the Queensland fruit fly Bactrocera tryoni (Froggatt), has been analysed over a five year period (1994–1998), using six microsatellites. Adult fly samples were collected to cover most regions of eastern and central Australia where the flies are regularly found. Tests for heterogeneity indicated that flies within geographically defined regions were homogeneous. The samples were allocated into five regions, including one very large region, Queensland, which encompasses that portion of the fly‘s range where breeding can occur year-round. With one exception, the collections from different regions were homogeneous between years, showing a fairly static distribution of the species. However, differences between regions were highly significant. The one case of a change in frequency between years indicated a gradual replacement of flies in a marginal region by flies from the main part of the range. The finding of stability in the distribution of a highly mobile insect is of interest, potentially also for other species which have expanded beyond their native range. It is argued that a contributing reason for this stability may be adaptation to different climatic regimes, and that strategies for control based on this hypothesis afford a reasonable chance of success.
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