A preliminary study of a promising bi-layer environmental barrier coating (EBC) designed to reduce the susceptibility of SiC composites to hot water vapor erosion is reported. The EBC system consisted of a silicon bond coat and a pore-free ytterbium disilicate (YbDS; Yb 2 Si 2 O 7 ) topcoat. Both layers were deposited on -SiC substrates using a recently optimized air plasma spray method. The two layers of the coating system had coefficients of thermal expansion (CTE) that were well matched to that of the substrate, while the YbDS has been reported to have a moderate resistance to silicon hydroxide vapor forming reactions in water vapor rich environments. Thermal cycling experiments were conducted between 110 °C and 1316 °C in a flowing 90 % H 2 O/10 % O 2 atmospheric pressure environment, and resulted in the formation of a thermally grown (silica) oxide (TGO) at the silicon-ytterbium disilicate interface. The TGO layer exhibited linear oxidation kinetics consistent with oxidizer diffusion through the ytterbium silicate layer controlling its thickening rate. The effective diffusion coefficient of the oxidizing species in the YbDS layer was estimated to be 2x10 -12 m 2 s -1 at 1316 o C. Slow steam volatilization of the YbDS topcoat resulted in the formation of a thin, partially protective, high CTE ytterbium monosilicate layer on the outside of the YbDS coating. Progressive edge delamination of the coating system was observed with steam exposure time, consistent with water vapor volatilization of the TGO edges that were directly exposed to the environment. This was aided by outward bending of the delaminated region to relax TGO and YbMS surface layer stresses developed during the cooling phase of each thermal cycle.

A new spontaneous mouse mutation named fierce (frc) is deleted for the nuclear receptor Nr2e1 gene (also known as Tlx, mouse homolog of Drosophila tailless). The fierce mutation is genetically and phenotypically similar to Nr2e1 targeted mutations previously studied on segregating genetic backgrounds. However, we have characterized the fierce brain, eye, and behavioural phenotypes on three defined genetic backgrounds (C57BL/6J, 129P3/JEms, and B6129F1). The data revealed many novel and background-dependent phenotypic characteristics. Whereas abnormalities in brain development, hypoplasia of cerebrum and olfactory lobes, were consistent on all three backgrounds, our novel finding of enlarged ventricles in 100% and overt hydrocephalus in up to 30% of fierce mice were unique to the C57BL/6J background. Developmental eye abnormalities were also background-dependent with B6129F1-frc mice having less severe thinning of optic layers and less affected electroretinogram responses. Impaired regression of hyaloid vessels was observed in all backgrounds. Furthermore, retinal vessels were deficient in size and number in 129P3/JEms-frc and B6129F1-frc mice but almost entirely absent in C57BL/6J-frc mice. We present the first standardized behavioural tests conducted on Nr2e1 mutant mice and show that C57BL/6J-frc and B6129F1-frc mice have deficits in sensorimotor assays and are hyperaggressive in both sexes and backgrounds. However, C57BL/6J-frc mice were significantly more aggressive than B6129F1-frc mice. Overall, this extensive characterization of the fierce mutation is essential to its application for the study of behavioural, and brain and eye developmental disorders. In addition, the background-dependent differences revealed will enable the identification of important genetic modifiers.

Animals restrict breeding to specific times of the year when reproductive success is most likely. In males, the most reliable method of reproductive inhibition is gonadal retrogression to an immature state. Depending on the species, the testes decrease in size by between 10 and 95% in response to environmental cues associated with the non-breeding season. An increased rate of apoptosis can occur during testicular regression, whereas little testicular apoptosis is observed during testicular recrudescence or during the breeding season. The Fas system is implicated as a potential mechanism to transmit the apoptotic signal to germ cells during regression, although many apoptotic pathways probably contribute to testicular regression. Finally, differences in both the contribution of testosterone and in the types of cell that undergo apoptosis differ between rodents and birds, indicating that different cellular mechanisms and possibly signals have evolved at the testis to suspend reproduction on a seasonal basis.

Siberian hamster reproduction is mediated by photoperiod-induced changes in gonadal activity. However, little is known about how photoperiod induces cellular changes in ovarian function. We hypothesized that exposing female hamsters to short (inhibitory) as opposed to long (control) photoperiods would induce an apoptosis-mediated disruption of ovarian function. Ovaries and plasma from hamsters exposed to either long (LD, 16 h light:8 h darkness) or short (SD, 8 h light:16 h darkness) days were collected during diestrus II after 3, 6, 9 and 12 weeks and processed for histology or RIA respectively. Apoptosis was assessed by in situ TUNEL and active caspase-3 protein immunolabeling. No significant differences were observed among LD hamsters for any parameter; therefore, these control data were pooled. SD exposure induced a decline in preantral follicles (P < 0.05), early antral/antral follicles (P < 0.01) and corpora lutea (P < 0.01) by week 12 as compared with LD. Terminal atretic follicles appeared by SD week 9; by week 12, these had become the predominant ovarian structures. Estradiol concentrations decreased by weeks 9 and 12 SD when compared with both LD and week-3 SD hamsters (P < 0.05); however, no changes were observed for progesterone. TUNEL-positive follicles in SD ovaries increased at week 3 and subsequently declined by week 12 as compared with LD ovaries (P < 0.01). Active capsase-3 protein immunostaining peaked at SD week 3 as compared with all other groups (P < 0.01). TUNEL and capsase-3 immunolabeling were localized to granulosa cells of late-preantral and early-antral/antral follicles. These data indicate that SD exposure rapidly induces follicular apoptosis in Siberian hamsters, which ultimately disrupts both estradiol secretion and folliculogenesis, resulting in the seasonal loss of ovarian function. IntroductionTo maximize survival when environmental resources are reduced, individuals of many temperate species limit reproductive function seasonally. In mammals, this adaptation is cued primarily by photoperiod-induced alterations in melatonin secretion from the pineal gland. For long-day (LD) seasonal breeders, such as Siberian hamsters (Phodopus sungorus), exposure to long photoperiods (. 12.5 h of light per day; short duration of melatonin release) induces and maintains reproductive function, whereas exposure to short photoperiods (, 12.5 h of light per day; long duration of melatonin release) results in the cessation of reproductive function (Hoffmann 1986, Bronson 1989, Knopper & Boily 2000, Prendergast & Nelson 2001. Extended periods of melatonin secretion negatively affect reproductive activity via inhibition of the hypothalamic-pituitary-gonadal (HPG) axis. In both males and females, short-day (SD) exposure reduces hypothalamic synthesis and secretion of gonadotropin-releasing hormone (GnRH) and, subsequently, the pituitary gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) (Glass 1986, Buchanan & Yellon 1991. Eventually, these endocrine alterations resu...

Many small, nontropical mammals stop breeding during winter. Chronic exposure of males to short days (<12.5 h light/day) causes the testes to atrophy and both steroidogenesis and gametogenesis to decrease. Male white-footed mice (Peromyscus leucopus) exposed to inhibitory short day lengths provide a natural animal model to study the cellular mechanisms regulating testicular regression. In the present study, the possible role of apoptosis was assessed during naturally occurring, short day-induced gonadal regression in white-footed mice by in situ terminal transferase-mediated end labeling (TUNEL), quantitative DNA 3'-end-labeling autoradiography (laddering) of DNA fragments, and quantification of Fas protein expression, an early initiator of apoptosis. Sexually mature male mice were exposed to short (8 h of light, 16 h of darkness) or long (16 h of light, 8 h of darkness) day lengths for 2, 4, 6, 8, or 10 weeks; gonads were then removed and processed for detection of apoptotic activity. In common with previous studies, the first significant reduction in relative testis mass was observed at week 10 of short day exposure. A 2- to 3-fold increase in apoptotic (TUNEL-positive) germ cells per seminiferous tubule was observed in the testes of mice exposed to short days for 4, 6, 8, or 10 weeks compared with the testes of long day animals. The extent of 3'-end labeling of low mol wt DNA increased with 4-8 weeks of short day exposure. Western blot analysis revealed an up-regulation of the Fas protein in the testes of short day males at 4, 8, and 10 weeks. Fas staining was primarily localized to spermatocytes and spermatids. Plasma testosterone concentrations decreased in short compared with long day animals after 6, 8, or 10 weeks. The increase in TUNEL positive-labeled germ cells, testicular DNA fragmentation, and up-regulation of the Fas protein before short day reductions of testis mass and function suggest that apoptosis is important for the mediation of photoperiod-induced testicular regression in white-footed mice.

The matrix metalloproteinases (MMPs) are a family of extracellular matrix-cleaving enzymes involved in ovarian remodeling. In many non-tropical species, including Siberian hamsters, ovarian remodeling is necessary for the functional changes associated with seasonal reproduction. We evaluated MMPs and their endogenous inhibitors (TIMPs), during photoperiod-induced ovarian recrudescence in Siberian hamsters. Hamsters were transferred from long-day (LD;16:8) to shortday (SD;8:16) photoperiods for 14wks, and then returned to LD for 0,1,2,4, or 8wks for collection of ovaries and plasma. Post-transfer (PT) LD exposure increased body and ovarian mass. Numbers of corpora lutea and antral, but not preantral follicles increased in PT groups. Plasma estradiol concentrations were lower in PT wks0−4, and returned to LD levels at PTwk8. No change was observed in relative MMP/TIMP mRNA levels at PTwk0 (SDwk14) as compared to LD. Photostimulation increased MMP-2 mRNA at PTwk8 as compared to PT wks 0−1. MMP-14 mRNA expression peaked at PTwks1−2 as compared to LD levels, while MMP-13 expression was low during this time. TIMP-1 mRNA peaked at PT wk8 as compared to PTwks0−4. No changes were noted in MMP-9 and TIMP-2 mRNA expression. In general, MMP/TIMP protein immunodetection followed the same patterns with most staining occurring in granulosa cells of follicles and corpora lutea. Our data suggest that mRNA and protein for several members of the MMP/TIMP families are expressed in Siberian hamster ovaries during recrudescence. Because of the variation observed in expression patterns, MMPs and TIMPs may be differentially involved with photo-stimulated return to ovarian function.

Matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) may be involved in tissue remodelling in the primate corpus luteum (CL). MMP/TIMP mRNA and protein patterns were examined using real-time PCR and immunohistochemistry in the early, mid-, mid-late, late and very late CL of rhesus monkeys. MMP-1 (interstitial collagenase) mRNA expression peaked (by >7-fold) in the early CL. MMP-9 (gelatinase B) mRNA expression was low in the early CL, but increased 41-fold by the very late stage. MMP-2 (gelatinase A) mRNA expression tended to increase in late CL. TIMP-1 mRNA was highly expressed in the CL, until declining 21-fold by the very late stage. TIMP-2 mRNA expression was high through the mid-luteal phase. MMP-1 protein was detected by immunocytochemistry in early steroidogenic cells. MMP-2 protein was prominent in late, but not early CL microvasculature. MMP-9 protein was noted in early CL and labelling increased in later stage steroidogenic cells. TIMP-1 and -2 proteins were detected in steroidogenic cells at all stages. Thus, MMPs and TIMPs are dynamically expressed in a cell-specific manner in the primate CL. Early expression of MMP-1 is suggestive of a role in tissue remodelling associated with luteinization, whereas MMP-2 and -9 may contribute to later stage luteolysis. TIMP expression may control MMP activity, until declining at luteolysis.

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