Two Methods of Vitrification Followed byIn VitroCulture of the Ovine Ovary: Evaluation of the Follicular Development and Ovarian Extracellular Matrix

Systematic review and meta-analysis on patented and non-patented vitrification processes to ovarian tissue reported between 2000 and 2021

Due to the great interest in ovarian cryopreservation and, consequently conservation and restoration of female fertility in the last decades, different vitrification procedures (vitrification devices or solutions) have been developed, patented, and used both for academic research purposes and for clinical use. Therefore, the present study aimed to provide a systematic review and meta-analysis of data obtained from the application of different patented and non-patented vitrification devices and solutions in different countries. For this purpose, relevant observational studies published between the years 2000 to 2021 were selected to verify the efficiency of ovarian vitrification processes on parameters such as morphology, viability, and apoptosis in preantral ovarian follicles after transplantation or in vitro culture. Our research revealed that, although several countries were considered in the study, the United States and Japan were the countries that registered the most processes, and 22 and 16 vitrification devices and solutions out of a total of 51, respectively were patented. Sixty-two non-patented processes were also considered in the study in all countries. We also observed that transplantation and in vitro ovarian culture were the techniques predominantly used to evaluate the efficiency of the devices and vitrification solutions, respectively. In conclusion, this review showed that patented or non-patented protocols available in the literature are able to successfully preserve preantral follicles present in ovarian tissue. Despite the satisfactory results reported so far, adjustments in ovarian vitrification protocols in order to minimize cryoinjuries to the follicles remain one of the goals of cryopreservation and preservation of the female reproductive function. We found that vitrification alters the morphology and viability, and offers risks leading in some cases to follicular apoptosis. However, adjustments to current protocols to develop an optimal procedure can minimize damage by not compromising follicular development after vitrification/warming.

Microbiological load and preantral follicle preservation using different systems for ovarian tissue vitrification in the red-rumped agouti

We evaluated the effect of open and closed systems used for ovarian tissue vitrification on the microbiological load and preservation of preantral follicles (PAFs) in the red-rumped agoutis. The ovaries from eight females were recovered and fragmented, with four cortexes fragments immediately fixed and evaluated (fresh group). The other fragments were processed for the solid-surface vitrification method (SSV) or an ovarian tissue cryosystem (OTC) using fetal calf serum, ethylene glycol, and sucrose as cryoprotectants, stored for two weeks, and rewarmed. Subsequently, fragments were subjected to a 24-h in vitro culture and assessed for microbiological load, PAF morphology, and DNA integrity. There was no fungal contamination; however, the vitrified samples from two individuals showed bacterial contamination of 79 200 colony forming units per milliliter (CFU)/mL for SSV and 3120 CFU/mL for OTC. From those samples, a total of eight different types of bacterial colonies were isolated and identified as coagulase-negative Staphylococci and Gram-positive bacilli. Regarding PAF morphology, both systems provided adequate preservation, with values higher than 70% normal follicles observed before and after culture. The TUNEL assay revealed that both SSV (52.39%) and OTC (41.67%) could preserve DNA integrity after vitrification and after 24 h of culture. In summary, both open and closed systems were equally efficient in preserving agouti ovarian tissues, especially concerning the preantral follicle morphology and DNA integrity; however, the OTC seems to provide a less adequate environment for bacterial proliferation.

Alpha Lipoic Acid Supplementation Improves Ovarian Tissue Vitrification Outcome: An Alternative to Preserve the Ovarian Function of Morada Nova Ewe

This study evaluated the effect of adding alpha lipoic acid (ALA) to the vitrification solution of sheep ovarian tissue on 7 days of in vitro culture or 15 days of xenotransplantion. ALA was used at two different concentrations (100 μM: ALA100 and 150 μM: ALA150). Ovarian tissue was evaluated by classical histology (follicular morphology, development, and stromal cell density); immunohistochemistry for forkhead box O3a (FOXO3a); Ki67 (cell proliferation); cluster of differentiation 31 (CD31); and alpha smooth muscle actin (α-SMA). Reactive oxygen species (ROS) levels in ovarian tissue, as well as malondialdehyde (MDA) and nitrite levels in the culture medium, were assessed. Similar percentage of morphologically normal follicles was found in the vitrified ovarian tissue in the presence of ALA100 or ALA150 after in vitro culture or xenotransplantation. Follicular development from all treatments was higher (P < 0.05) than the control group. Moreover, an activation of primordial follicles was observed by FOXO3a. Stromal cell density and immunostaining for Ki67 and CD31 were significantly higher (P < 0.05) in ALA150 vitrified tissue. No difference (P > 0.05) was found in α-SMA between ALA concentrations after in vitro culture or xenograft. ROS levels in the ovarian tissue were similar (P > 0.05) in all treatments, as well as MDA and nitrite levels after 7 days of culture. We concluded that the addition of ALA 150 is able to better preserve the stromal cell density favoring granulosa cell proliferation and neovascularization.

FSH promotes the proliferation of sheep granulosa cells by inhibiting the expression of TSP1

Thrombospondin (TSP1) plays an important role as an antiangiogenic factor in the reproductive system of female mammals. However, its expression and function in sheep are still unclear. In the present research, the Altay sheep (a native Chinese breed) was used to analyze the expression of TSP1 in the ovary and its potential function in granulosa cells. TSP1 was widely expressed in most tissues, as shown by qPCR. In the ovary, TSP1 mRNA expression decreased during follicular to luteal growth. The TSP1 protein was expressed in a wide variety of follicles of different diameters and localized to the cytoplasm and nucleus of granulosa cells. In in vitro studies, follicle-stimulating hormone (FSH) significantly inhibited the expression of TSP1 in sheep granulosa cells. Functionally, FSH- and TSP1-specific siRNAs can promote the proliferation of sheep granulosa cells. In contrast, TSP1 mimetic peptide, ABT510, offsets the proliferation of sheep granulosa cells. Different signaling pathway inhibitors all promoted FSH-inhibited TSP1 expression, but each inhibitor had different effects on TSP1. Among them, the PI3K and ERK pathway inhibitors significantly promoted TSP1 expression and inhibited the proliferation of sheep granulosa cells.

Heterotopic ovarian allotransplantation in goats: Preantral follicle viability and tissue remodeling

An appropriate implantation site favors angiogenesis and avoids ovarian tissue damage after tissue grafting. The objective of this study was to evaluate the effects of intramuscular (IM) and subcutaneous (SC) sites for ovarian grafts in goats by evaluating follicular morphology and activation, preantral follicle and stromal cell densities, tissue DNA fragmentation, collagen types I and III depositions, and graft revascularizations. Ovarian cortical tissue was transplanted in IM or SC sites and recovered 7 or 15 days post-transplantation. There was a greater percentage of developing follicles and lesser follicular and stromal cell densities in all grafted tissues as compared to ovarian tissues of the control group. The stromal cell density and percentage of normal follicles were positively associated. At 15 days post-transplantation, tissues at the SC and IM sites had similar amounts of DNA fragmentation and type III collagen content. In contrast, tissues at the SC, as compared with IM site, had greater abundances of collagen type I. Furthermore, there was a positive association between collagen type I and percentage of morphologically normal follicles post-transplantation. In addition to a marked decrease in follicular density 15 days post-transplantation in ovarian grafts at the SC and IM sites, low percentages of normal follicles and follicular activation were observed similarly in both transplantation sites. There were also positive associations of stromal cell density and abundance of type I collagen fibers with the percentage of intact follicles in grafted ovarian tissues.

Use of synthetic polymers improves the quality of vitrified caprine preantral follicles in the ovarian tissue

The aim of this study was to evaluate whether the addition of synthetic polymers to the vitrification solution affected follicular morphology and development and the expression of Ki-67, Aquaporin 3 (AQP3) and cleaved Caspase-3 proteins in ovarian tissue of the caprine species. Caprine ovaries were fragmented and two fragments were immediately fixed (Fresh Control) for morphological evaluation, while other two were in vitro cultured for 7 days (Cultured Control) and fixed as well. The remaining fragments were distributed in two different vitrification groups: Vitrified and Vitrified/Cultured. Each group was composed of 4 different treatments: 1) Sucrose (SUC); 2) SuperCool X-1000 0.2 % (X-1000); 3) SuperCool Z-1000 0.4 % (Z-1000) or 4) with polyvinylpyrrolidone K-12 0.2 % (PVP). Also, Fresh Control, Cultured Control, SUC and X-1000 were destined to immunohistochemical detection of Ki-67, AQP3 and cleaved Caspase-3 proteins. Morphologically, the treatment with X-1000 showed no significant difference with the Fresh Control group and was superior to the other treatments. After the cleaved caspase-3 analysis, X-1000 showed the lowest percentages of strong immunostaining while Cultured Control showed the highest. Also, a positive correlation was found between the percentages of degenerated follicles and the percentages of strong staining intensity follicles. Regarding the AQP3 analysis, the highest percentages of strong AQP3 staining intensity were found in X-1000. In conclusion, we have demonstrated that the addition of the synthetic polymer SuperCool X-1000 to the vitrification solution improved the current vitrification protocol of caprine ovarian tissue.

Morphometric and gene expression analyses of stromal expansion during development of the bovine fetal ovary

During ovarian development stroma from the mesonephros penetrates and expands into the ovarian primordium and thus appears to be involved, at least physically, in the formation of ovigerous cords, follicles and surface epithelium. Cortical stromal development during gestation in bovine fetal ovaries (n=27) was characterised by immunohistochemistry and by mRNA analyses. Stroma was identified by immunostaining of stromal matrix collagen type I and proliferating cells were identified by Ki67 expression. The cortical and medullar volume expanded across gestation, with the rate of cortical expansion slowing over time. During gestation, the proportion of stroma in the cortex and total volume in the cortex significantly increased (P<0.05). The proliferation index and numerical density of proliferating cells in the stroma significantly decreased (P<0.05), whereas the numerical density of cells in the stroma did not change (P>0.05). The expression levels of 12 genes out of 18 examined, including osteoglycin (OGN) and lumican (LUM), were significantly increased later in development (P<0.05) and the expression of many genes was positively correlated with other genes and with gestational age. Thus, the rate of cortical stromal expansion peaked in early gestation due to cell proliferation, whilst late in development expression of extracellular matrix genes increased.

Vitrification of collared peccary ovarian tissue using open or closed systems and different intracellular cryoprotectants

This study aimed to evaluate different vitrification methods using distinct cryoprotectants (CPAs) for the preservation of collared peccary ovarian preantral follicles (PFs). Ovarian pairs from six females were fragmented and three fragments (fresh control group) were immediately evaluated for morphology, viability, cell proliferation capacity (assessed by quantifying the number of argyrophilic nucleolus organizer regions - NORs), and apoptosis (by the identification of activated caspase-3 expression). The remaining 18 fragments were vitrified using the solid surface vitrification (SSV) method or the ovarian tissue cryosystem (OTC) with 3 M ethylene glycol (EG), 3 M dimethylsulfoxide (DMSO), or a combination of the two (1.5 M EG/1.5 M DMSO). After two weeks, samples were rewarmed and evaluated as described previously. The OTC with any of the CPAs provided a similar conservation of morphologically normal PFs as the fresh control group (75.6 ± 8.6%); however, the SSV was only efficient with DMSO alone (63.9 ± 7.6%). Regarding the viability or cell proliferation, all tested groups provided post rewarming values similar to those observed for the fresh control group, 84.0 ± 2.9% viable cells with 2.0 ± 0.2 NORs. Related to apoptosis analysis, only the OTC with EG (46.7%) and the SSV method with EG (43.4%) or the combination of EG and DMSO (33.4%) provided similar values to those found for the fresh control group (36.7%). Our findings indicate the utilization of a closed system, the OTC, with 3 M EG as the CPA for the vitrification of collared peccary ovarian tissue.

In vitro survival of follicles in prepubertal ewe ovarian cortex cryopreserved by slow freezing or non-equilibrium vitrification

PURPOSE

Vitrification is a well-accepted fertility preservation procedure for cryopreservation of oocytes and embryos but little is known regarding ovarian tissue, for which slow freezing is the current convention. The aim of the present study was to assess the efficiency of non-equilibrium vitrification compared to conventional slow freezing for ovarian cortex cryopreservation.

METHODS

Using prepubertal sheep ovaries, the capacity of the tissue to sustain folliculogenesis following cryopreservation and in vitro culture was evaluated. Ovarian cortex fragments were cultured in wells for 9 days, immediately or after cryopreservation by conventional slow freezing or non-equilibrium vitrification in straws. During culture, follicular populations within cortex were evaluated by histology and immunohistochemistry for PCNA and TUNEL. Steroidogenic activity of the tissue was monitored by assay for progesterone and estradiol in spent media.

RESULTS

No significant differences in follicle morphology, PCNA, or TUNEL labeling were observed between cryopreservation methods at the initiation of culture. Similar decreases in the proportion of primordial follicle population, and increases in the proportion of growing follicles, were observed following culture of fresh or cryopreserved ovarian tissue regardless of cryopreservation method. At the end of culture, PCNA and TUNEL-positive follicles were not statistically altered by slow freezing or vitrification in comparison to fresh cultured fragments.

CONCLUSIONS

Overall, for both cryopreservation methods, the cryopreserved tissue showed equal capacity to fresh tissue for supporting basal folliculogenesis in vitro. Taken together, these data confirm that both non-equilibrium vitrification and slow-freezing methods are both efficient for the cryopreservation of sheep ovarian cortex fragments.

Early ovine preantral follicles have a potential to grow until antral stage in two-step culture system in the presence of aqueous extract of Justicia insularis

The objective of this study was to determine whether preantral follicles cultured in vitro for 7 days within ovine ovarian cortical strips could be isolated at the secondary follicles (SF) and grown until antral stage during an additional 6 days period of in vitro culture in the presence of aqueous extract of Justicia insularis. Fresh ovarian fragments from 16 adult sheep were fixed for histological analysis (Control 1) or in vitro cultured individually in α-MEM⁺ supplemented with 0.3 mg/ml J. insularis (Step 1) for 7 days. Part of the fragments then were fixed for histological analysis (in vitro culture group). Remaining fragments were exposed stepwise to increasing trehalose concentrations before immediate isolation of SF and viability assessment (Control 2) or after 6 days of culture in α-MEM⁺⁺ supplemented with 0.3 mg/ml J. insularis (Step 2). In Step 1, percentage of follicular activation was 80%. In Step 2, a significant increase (p < 0.05) in follicular diameter and antrum formation within 6 days in vitro culture of isolated follicles was achieved. The total antioxidant capacity from both steps significantly increase (p < 0.05) from day 2 to day 6. Confocal analysis of oocytes showed 57.14% oocytes with homogeneous distribution and 42.86% with peri-cortical distribution. In conclusion, SF can be successfully isolated from sheep ovarian cortex after 7 days of culture and are capable of surviving and forming an antral cavity if cultured in vitro for an additional 6 days in the presence of 0.3 mg/ml J. insularis.

Development of fresh and vitrified agouti ovarian tissue after xenografting to ovariectomised severe combined immunodeficiency (SCID) mice

The aim of the present study was to evaluate the development of fresh and vitrified agouti ovarian tissue after xenografting to C57Bl/6 severe combined immunodeficiency (SCID) female mice. Ovaries were obtained from five female agoutis and divided into 16 fragments. Five fragments were transplanted immediately to ovariectomised SCID mice and the others were vitrified, stored for 2 weeks and transplanted only after rewarming. Tissue fragments were transplanted under the kidney capsule in recipients. The return of ovarian activity in recipients was monitored by the observation of external signs of oestrus and vaginal cytology over a period of 40 days after transplantation, after which the grafts were removed and evaluated for morphology, cell proliferation and the occurrence of DNA fragmentation. Ovarian activity returned in four of five mice that received fresh ovarian tissue from agoutis and in one of six mice that had received vitrified tissue a mean (±s.e.m.) 20.6±8.6 days after xenotransplantation. After graft removal, a predominance of primordial and primary follicles was observed in all grafts. Vitrification reduced cell proliferation and increased the occurrence of DNA fragmentation in grafted agouti ovarian tissue. In conclusion, the present study demonstrates that xenografted agouti ovarian tissue, fresh or vitrified, is able to promote the return of ovarian activity in ovariectomised SCID C57B1/6 mice. However, improvements to vitrification protocols for agouti ovarian tissue are necessary.

Vitrification of testicular tissue from prepubertal cats in cryotubes using different cryoprotectant associations

Protocols for the cryopreservation of testicular tissue are not yet established. In cats, few studies have been conducted on testicular vitrification using different cryoprotectant associations (CPAs). Thus, the objective of this study was to compare the effect of different CPAs on the vitrification of testicular tissue from prepubertal cats in cryotubes. We used 10 pairs of testicles, with each pair divided into 8 fragments that were distributed into different experimental groups. Two of these fragments were allocated into the control group (CG) and the other six were distributed according to the CPAs to be tested (dimethyl sulfoxide (DMSO)/glycerol (GLY), ethylene glycol (EG)/GLY, or DMSO/EG). The cryoprotectants were used at a final concentration of 5.6 M. The fragments were subjected to vitrification in cryotubes and after 1 week, they were warmed and processed for histomorphologic assessment, quantification of nucleolar organizer regions (NORs), and determination of cell viability. The DMSO/EG and EG/GLY groups presented the greatest cell separation from the cell basement membrane and the highest degrees of retraction of the basal membrane. In these aspects, DMSO/GLY did not differ from the CG and both were significantly superior to the other groups. In terms of cell distinction, visibility of the nucleus, and nuclear condensation, all the vitrified groups had significantly lower values than the CG, while the DMSO/GLY and EG/GLY groups did not differ between themselves. Through the quantification of NORs, the potential for cell proliferation of the CG was found to have a mean of 3.80, while DMSO/GLY presented a mean of 3.60, and thus there was no significant difference between these two groups. The proliferation potentials of both groups were significantly superior to that of the DMSO/EG (mean: 2.07) and EG/GLY (mean: 1.98) groups. In the CG and DMSO/GLY group, 91.8% and 64.2% of cells, respectively, were found to be viable. The cell viabilities of both groups were significantly superior to those of DMSO/EG (52.5%) and EG/GLY (57.10%). Vitrification in cryotubes combined with the use of the DMSO/GLY association was effective in maintaining the histomorphology, cell proliferation potential, and cell viability of testicular tissue from prepubertal cats after cryopreservation.

In vivo and in vitro strategies to support caprine preantral follicle development after ovarian tissue vitrification

The aim of the present study was to compare fresh and vitrified goat ovarian tissue after autotransplantation and in vitro culture. Adult goats were completely ovariectomised and each ovarian pair was sliced and distributed among six different treatment groups: fresh control, fresh transplant, fresh culture, vitrified control, vitrified transplant and vitrified culture. Follicular morphology, development, growth, density, revascularisation and hormone production were evaluated in all groups. Three antral follicles (two in the fresh transplant and one in the vitrified transplant groups) were observed on the surface of the graft 90 days after transplantation. The percentage of morphologically normal follicles was similar in the fresh control, fresh transplant and vitrified transplant groups. The percentage of developing (transition, primary and secondary) follicles was higher after in vitro culture of fresh or vitrified tissue. Transplantation resulted in a lower follicle density. Serum oestradiol concentrations remained constant during the entire transplantation period. In contrast, progesterone production decreased significantly. Expression of CD31 mRNA was lower in fresh culture. In conclusion, restoration of goat ovarian function can be successfully achieved following transplantation of both fresh and vitrified goat ovarian tissue. However, transplantation induced higher follicle loss than in vitro culture.

Unexpected effect of the vehicle (grain ethanol) of homeopathic FSH on the in vitro survival and development of isolated ovine preantral follicles

The aims of this study were to investigate the effects of medium replacement system (experiment I) and of FSH presentations (homeopathic - FSH 6cH and allopathic FSH - rFSH; experiment II) on the in vitro development, hormone production and gene expression of isolated ovine preantral follicles cultured for 6 days. In experiment I, secondary follicles were cultured in the α-MEM+ supplemented with FSH 6cH (0.05 fg/ml) or recombinant bovine FSH (100 ng/ml) without/with daily medium addition. The homeopathic FSH treatments with/without medium addition improved (p < .05) follicular development compared to rFSH100 treatment without addition. FSH 6cH with addition showed the highest (p < .05) estradiol production. To verify whether the effects of homeopathic FSH were not due to its vehicle, experiment II was performed. The α-MEM+ was supplemented or not with alcohol (0.2% grain ethanol, v/v), FSH 6cH or rFSH100 with daily medium addition. Surprisingly, we found that all treatments improved follicular development compared to the α-MEM+ (p < .05). Moreover, homeopathic FSH was similar to the other treatments including its vehicle. In conclusion, its vehicle (ethanol) causes the effect of homeopathic FSH on in vitro development of isolated ovine preantral follicles.

Connexin 37 and 43 gene and protein expression and developmental competence of isolated ovine secondary follicles cultured in vitro after vitrification of ovarian tissue

Cryoinjuries caused by vitrification of tissues and organs lead to the loss of membrane proteins that mediate intercellular communications, such as connexins 37 (Cx37) and 43 (Cx43). Thus, the present study aimed to evaluate ovine Cx37 and Cx43 gene and protein expressions and developmental competence by in vitro-cultured secondary follicles retrieved from vitrified ovarian tissue. Ovarian fragments for the same ovary pair were distributed into six treatments: (1) fresh ovarian tissue (FOT); (2) vitrified ovarian tissue (VOT); (3) isolated follicles from fresh ovarian tissue (FIF); (4) isolated follicles from vitrified ovarian tissue; (5) isolated follicles from fresh ovarian tissue followed by in vitro culture (CFIF); (6) isolated follicles from vitrified ovarian tissue followed by in vitro culture (CVIF). In all treatments, Cx37 and Cx43 gene and protein expression patterns were evaluated by reverse transcription polymerase chain reaction and immunocytochemistry. In addition, secondary follicles were analyzed according to follicular integrity and growth, apoptosis, and cell proliferation. In vitro-cultured secondary follicles (CFIF and CVIF) were evaluated based on morphology (extruded follicles), antrum formation, and viability. The percentage of intact follicles was higher, whereas antrum formation, oocyte extrusion rate, and follicle viability were lower in CVIF than in CFIF treatment (P < 0.05). Terminal deoxynucleotidyl transferase-mediated biotinylated deoxyuridine triphosphates nick end-labeling assay demonstrated that apoptosis was absent in FIF, whereas follicles from all other treatments showed positive labeling. Cell proliferation index was higher in isolated follicles from vitrified ovarian tissue and CVIF treatments than in follicles from FIF. Expression of Cx43 messenger RNA was lower in CVIF treatment when compared with follicles from all other treatments (P < 0.05). Follicle Cx37 messenger RNA levels did not show alterations in any treatment (P > 0.05). Cx37 and Cx43 immunolabeling was localized mainly on granulosa cells and oocytes, respectively. In conclusion, isolation of ovine secondary follicles could be done successfully after vitrification of ovarian tissue, and the basement membrane integrity remained intact after in vitro culture. Although the gene and protein expression of Cx37 did not change after vitrification of ovarian tissue, Cx43 turned out to be altered in secondary follicles after vitrification and in vitro culture.

Modulation of aquaporins 3 and 9 after exposure of ovine ovarian tissue to cryoprotectants followed by in vitro culture

Our aim has been to evaluate the effect of cryoprotective agents (CPAs) on the exposure, vitrification (VIT), and in vitro culture (IVC) of ovarian tissue with regard to the expression and immunolocalization of aquaporins (AQPs) 3 and 9 in ovine preantral follicles. Tissues were treated as follows: Experiment I: (1) control (without exposure to CPAs), (2) e-EG (exposure to ethylene glycol), (3) er-EG (exposure to and removal of EG), (4) e-DMSO (exposure to dimethyl sulfoxide), (5) er-DMSO (exposure to and removal of DMSO), (6) e-EG+DMSO (exposure to EG+DMSO), (7) er-EG+DMSO (exposure to and removal of EG+DMSO); Experiment II: (1) control, (2) VIT, (3) IVC, (4) VIT-IVC. In Experiment I, following er-EG or er-DMSO, tissue showed the down-regulation (P < 0.05) of AQP3 mRNA. The mRNA transcript levels were reduced (P < 0.05) for AQP9 in tissue following er-EG+DMSO. Immunolocalization was positive for both proteins (AQP3 and AQP9) on ovine preantral follicles following all treatments, except in the e-EG+DMSO group. In Experiment II, the mRNA levels of AQP3 and AQP9 following VIT treatment were similar (P > 0.05) to that of the control group. Nevertheless, VIT-IVC treatment led to the down-regulation of mRNA of AQP3 and AQP9. Thus, AQP3 and AQP9 act in a mutually dependent way, maintaining the cell homeostasis that is essential for the ovary cryopreservation process. Furthermore, the changes in the expression profiles of mRNA and protein after culture are a strong indicator that in vitro conditions have to be strictly controlled to ensure follicle viability and functionality.