Prepubertal and pubertal changes in the hamster ovary

Expression and prognostic significance of CBX2 in colorectal cancer: database mining for CBX family members in malignancies and vitro analyses

Background

The Chromobox (CBX) domain protein family, a core component of polycomb repressive complexes 1, is involved in transcriptional repression, cell differentiation, and program development by binding to methylated histone tails. Each CBX family member plays a distinct role in various biological processes through their own specific chromatin domains, due to differences in conserved sequences of the CBX proteins. It has been demonstrated that colorectal cancer (CRC) is a multiple-step biological evolutionary process, whereas the roles of the CBX family in CRC remain largely unclear.

Methods

In the present study, the expression and prognostic significance of the CBX family in CRC were systematically analyzed through a series of online databases, including Cancer Cell Line Encyclopedia (CCLE), Oncomine, Human Protein Atlas (HPA), and Gene Expression Profiling Interactive Analysis (GEPIA). For in vitro verification, we performed cell cloning, flow cytometry and transwell experiments to verify the proliferation and invasion ability of CRC cells after knocking down CBX2.

Results

Most CBX proteins were found to be highly expressed in CRC, but only the elevated expression of CBX2 could be associated with poor prognosis in patients with CRC. Further examination of the role of CBX2 in CRC was performed through several in vitro experiments. CBX2 was overexpressed in CRC cell lines via the CCLE database and the results were verified by RT-qPCR. Moreover, the knockdown of CBX2 significantly suppressed CRC cell proliferation and invasion. Furthermore, the downregulation of CBX2 was found to promote CRC cell apoptosis.

Conclusions

Based on these findings, CBX2 may function as an oncogene and potential prognostic biomarker. Thus, the association between the abnormal expression of CBX2 and the initiation of CRC deserves further exploration.

Aspects of follicle and oocyte stage that affect in vitro maturation and development of bovine oocytes

Success of in vitro maturation (IVM) and production of bovine embryos as related to aspects of follicle source and oocyte size were evaluated. First, it was determined that bovine oocytes continue growing in all follicular sizes studied, including >1- to 15-mm follicles. Populations of oocytes were collected from surface visible (peripheral) and cortical follicles from the same ovaries. When the number of oocytes from both peripheral and cortical follicles was combined, the yield of oocytes was approximately double that collected from 1 ovarian site alone. Oocytes from cortical follicles were smaller than those from the surface population, and the smaller cortical oocytes had a lower potential for both meiotic maturation and embryo development Only cortical oocytes with the largest diameters underwent IVM and subsequently developed to blastocysts at rates comparable to oocytes from peripheral follicles. As the diameter of the oocytes recovered from peripheral follicles increased, so did their developmental potential. When the stage of the estrous cycle was observed, it was found to have no effect on developmental potential. Finally, oocytes which extruded polar bodies at an earlier time during maturation were, on average, larger than those which extruded polar bodies later. The results serve a practical purpose in assisting selection of oocytes capable of developing into blastocysts and they give useful correlates of oocyte competencies based on knowledge of follicle source and oocyte stage.

Developmental expression of cytochrome P450 side-chain cleavage and cytochrome P450 17 alpha-hydroxylase messenger ribonucleic acid and protein in the neonatal hamster ovary

The temporal and spatial expression of cytochrome P450 side-chain cleavage (CYP11A1) and cytochrome P450 17 alpha-hydroxylase (CYP17) mRNA and protein during thecal cell differentiation in developing hamster ovaries were evaluated by reverse transcription-polymerase chain reaction (RT-PCR) and immunofluorescence histochemistry, respectively. Ovaries were collected from 15-day fetal through 20-day-old postnatal hamsters and used either for immunofluorescence detection of enzyme protein or RT-PCR evaluation of enzyme mRNA. Immunoreactivity of CYP11A1 first appeared in the interstitial cells on Day 10 postnatal (PN), and the intensity increased significantly with further ovarian development beyond 11 days of age. In contrast, CYP17 immunostaining was first detected in a few interstitial cells closer to large preantral follicles by Day 12 PN, and their number increased appreciably by Day 14 PN. By age 18-20 days, CYP17-positive cells were localized primarily in the thecal layer of large preantral follicles. A low level of CYP17 and CYP11A1 mRNA was present in fetal ovaries. The CYP17 mRNA levels increased sharply by Day 1 PN but decreased to a low baseline level by Day 2 PN and remained low up to Day 9 PN. Both CYP11A1 and CYP17 mRNA levels increased significantly by Day 10 PN compared to Day 9 PN; however, the increase for CYP11A1 was greater than CYP17. The CYP11A1 mRNA levels decreased noticeably on Day 11 PN and remained relatively stable until Day 14 PN; however, mRNA levels started increasing by Day 15 PN and increased sharply by Day 17 PN onward, corresponding to the increase in CYP11A1 protein in the ovarian interstitium and thecal compartments. On the other hand, CYP17 mRNA expression increased progressively through Day 12 PN. A sharp increase in CYP17 mRNA was noted on Day 13 PN in conjunction with the morphological development of thecal cells; mRNA levels remained steady afterward. The correlation of the increase in enzyme mRNA and protein, especially of CYP17, with the morphological development of thecal layers suggests that the differentiation of interstitial cells into theca may be modulated by multilayered preantral follicles, and the expression of enzyme protein occurs prior to an increase in serum LH.

Expression of P450 side-chain cleavage (CYP11A1) and P450 17alpha-hydroxylase-17/20 lyase (CYP17) messenger ribonucleic acid in hamster primary interstitial cells in vitro: differential regulation of steroidogenesis by cyclic adenosine monophosphate

Interstitial cells in the neonatal hamster do not respond to LH in vitro; however, side-chain cleavage (CYP11A1) and 17alpha-hydroxylase (CYP17) enzyme proteins are expressed in these cells. The objective of the study was to evaluate whether the cAMP second messenger system was active in these cells and if cAMP upregulates the levels of CYP11A1 and CYP17 mRNA. Interstitial cells (ICs) were cultured for 96 h in the presence of 5% fetal bovine serum and then cultured in serum-free medium in the presence of LH, forskolin, or 8-Br-cAMP for 24 h. The accumulation of cAMP, progesterone, and androstenedione was measured by radioimmunoassay, whereas CYP11A1 and CYP17 mRNA levels were determined by a semiquantitative reverse transcription-polymerase chain reaction and Southern hybridization analysis. LH failed to induce either progesterone or androstenedione production; however, forskolin stimulated cAMP production by interstitial cells in a dose-dependent manner. Moreover, both forskolin and 8-Br-cAMP significantly elevated the levels of CYP11A1 and CYP17 mRNA and induced progesterone synthesis by the interstitial cell monolayer. Despite the increase in CYP17 mRNA levels by 8-Br-cAMP, no appreciable change was noted in androstenedione production. These results suggest that, in vitro, a fully functional adenylate cyclase system is present in cultured interstitial cells of the neonatal hamster and that cAMP can influence the expression of CYP11A1 and CYP17 genes; however, cultured cells do not appear to express LH receptors that are functionally linked to the adenylate cyclase system. Moreover, the translation of CYP17 mRNA may require additional factors, which may originate from maturing granulosa cells.

Development of primordial and prenatal follicles from undifferentiated somatic cells and oocytes in the hamster prenatal ovary in vitro: effect of insulin

Fetal hamster ovaries were cultured for up to 16 days in the presence or absence of various dosages of insulin to evaluate the induction of folliculogenesis in vitro. In the absence of insulin, a few primordial follicle-like structures appeared by the 4th day, and distinct primary follicles (stage 1) appeared by the 12th day of culture. The organelles in the oocytes and adjacent granulosa cells developed along with follicular growth. Moreover, gap junctions between the oocyte and somatic cell plasma membrane also developed as early as 8 days in culture. In the presence of 0.2 microg/ml insulin, primary follicles developed after 8 days, and approximately 4% secondary follicles with 2-3 layers of granulosa cells appeared after 16 days of culture. However, higher dosages (> 0.2 microg/ml) of insulin retarded primary follicle formation and induced the formation of primordial follicles with larger oocytes. An increased number of larger oocytes with a few granulosa cells accumulated at the periphery of the ovary. The results indicate that although primordial and primary follicles can develop after 12 days in vitro in the absence of exogenous insulin, the latter is required for timely progression of follicular development through primary and secondary stages.

The effects of pregnant mare serum gonadotropin on follicular development, mating and pregnancy in mink

Forty-four female ranch mink, maintained out-of-doors under standard conditions, were exposed to natural photoperiod supplemented with a period of artificial light from approximately 2300 hr to 0300 hr from early January to mid February. Breeding was initiated on March 1. After repeated attempts to breed the animals, it was determined that the likelihood of their breeding was very low, presumably due to the artificial and asynchronous long-day photoperiod. In an attempt to induce breeding, the mink were randomly assigned to one of four treatment groups: saline, 25 International Units (IU) PMSG, 37.5 IU PMSG and 50 IU PMSG. Significantly different (p less than 0.05) patterns of breeding success were observed following PMSG treatment. Approximately 90% of the 37.5 and 50 IU PMSG-treated females bred while only 30 to 50% of the females in the saline and 25 IU PMSG-treated groups bred. More importantly, there was a marked difference in successful pregnancies observed between the saline- and PMSG-treated animals. None of the saline-treated females bore offspring while 40% of the animals that were treated with PMSG gave birth, with litter size averaging between 4 and 5 kits per female. Histological evaluation of ovaries obtained from an additional 13 animals treated in a similar fashion demonstrated that PMSG treatment significantly increased the number of small follicles. These results demonstrate that the exogenous administration of PMSG has a potential application in increasing the reproductive efficiency of female mink with functional ovarian tissue yet rendered infertile due to other factors.

Acceleration of reproductive development in female Djungarian hamsters by adult males

Housing young female Djungarian hamsters (Phodopus campbelli) with an adult male accelerates uterine and ovarian development and there is a strong relationship between uterine weight and ovarian measures (e.g., follicular size). Uterine weights of females housed with an adult male for 10 days following weaning are comparable to values from females housed alone for 25 days. Removal of endogenous androgens by castration eliminated the capacity of adult males to accelerate reproductive development in young females and treatment of castrated males with exogenous androgens maintained the production of the acceleratory chemosignal. When adult male urine and ventral gland sebum were examined as possible sources for the acceleratory chemosignal, only male urine had an acceleratory effect on reproductive development. Thus, female Djungarian hamsters respond with accelerated reproductive development to androgen-dependent chemosignals in the urine of adult males. These mechanisms are similar to those found in several other rodents but contrast with the lack of such effects in the golden hamster (Mesocricetus auratus).

FSH-induced aromatase activity in hamster granulosa cells: effect of estradiol-17 beta in vitro

We have shown previously that estradiol-17 beta (E2) reduces number of ovulations in cyclic rats, induces atresia of the dominant preovulatory follicle in monkeys, and that the initial effects of this treatment include reduced viability and estrogen accumulation in vitro by aspirated granulosa cells (GC) from monkeys and hamsters. The present experiment was designed to determine whether the reduction in estrogen accumulation can be ascribed to a direct action of E2 on the aromatization of androgen to estrogen in vitro. Female hamsters were injected with 30 I.U. pregnant-mare serum gonadotropin i.p. and sacrificed 3 days later. GC were aspirated from the largest follicles and incubated for 48 h ("initial incubation" period) in the presence of human pituitary follicle-stimulating hormone (hFSH, 100 ng/ml). Following initial incubation, GC were further incubated for up to 24 h ("secondary incubation" period). During this subsequent incubation, medium was supplemented with 100 nM 3H-1 beta-androstenedione (3H-A4). Initial incubation with E2 at doses of 10 ng/ml, 100 ng/ml and 1 microgram E2/ml induced variability in GC response, and a maximal depression of approximately 70%. The inhibition by E2 of hamster GC function in vitro parallels that shown in vivo for both hamsters and monkeys, but contrasts with that shown for rats. Thus, hamsters may represent an appropriate model in which to study the atretogenic effects of E2 directly on antral follicle development.

Diminished steroidogenic response of hamster granulosa cells to estrogen in vitro

We have previously demonstrated that estrogen can exert inhibitory or atretogenic effects on the ovaries of both rats and rhesus monkeys in vivo. This study was designed to test whether the hamster (Mesocricetus auratus) is an appropriate model in which to test the effects of estrogens (diethylstilbestrol and estradiol-17 beta) on steroid accumulation by ovarian granulosa cells in vitro, and whether the effects are similar to those demonstrated for other species in vivo. Immature female hamsters were injected with pregnant mare's serum gonadotropin at 28 to 30 days of age. Animals were sacrificed and follicular contents aspirated three days later. Granulosa cells were either left untreated or treated with diethylstilbestrol or estradiol (1 X 10(-7) M) in vitro for 72 h in the presence of androstenedione (1 X 10(-7) M, and in the presence or absence of serum (10%) or human follicle-stimulating hormone (20 ng/ml), and long-term accumulation of estrogen and progesterone was determined. Diethylstilbestrol inhibited accumulation of estrogen regardless of the presence or absence of follicle-stimulating hormone. In contrast, only estradiol plus follicle-stimulating hormone augmented accumulation of progesterone by granulosa cells. These findings that estrogen can be non-stimulatory or inhibitory to function of granulosa cells in vitro parallel those shown in vivo. Our experimental approach may therefore represent an appropriate model for study of the direct effects of estradiol on the function of granulosa cells.

Corpus luteum: animal models of possible relevance to reproductive toxicology

The presence of a normally functioning corpus luteum is an essential requirement for the maintenance of gestation in mammals. The chief function of the corpus luteum in all species is to synthesize the steroid hormone progesterone that is necessary for implantation and for the subsequent development of the fetoplacental unit. Activation and maintenance of luteal function involve pituitary, placental, and ovarian hormones. Perturbation in the secretion and/or action of any of these luteotropins by exogenous compounds can profoundly affect the steroidogenic capacity of the corpus luteum. Abnormal luteal function causes failure of implantation and embryonic wastage. Both in vitro and in vivo models for assessing luteal function are available; while the former are more convenient, the model of choice for toxicological studies is one in which in vitro findings can be easily confirmed in whole animals in vivo. This article is concerned primarily with the techniques used in basic research that might be useful for the evaluation of luteal function in reproductive toxicology.