Reference standards for follicular density in ovarian cortex from birth to sexual maturity.

RESEARCH QUESTION: Are age-normalized reference values for human ovarian cortical follicular density adequate for tissue quality control in fertility preservation? DESIGN: Published quantitative data on the number of follicles in samples without known ovarian pathology were converted into cortical densities to create reference values. Next, a sample cohort of 126 girls (age 1-24 years, mean ± SD 11 ± 6) with cancer, severe haematological disease or Turner syndrome were used to calculate Z-scores for cortical follicular density based on the reference values. RESULTS: No difference was observed between Z-scores in samples from untreated patients (0.3 ± 3.5, n = 30) and patients treated with (0.5 ± 2.9, n = 48) and without (0.1 ± 1.3, n = 6) alkylating chemotherapy. Z-scores were not correlated with increasing cumulative exposure to cytostatics. Nevertheless, Z-scores in young treated patients (0-2 years -2.1 ± 3.1, n = 10, P = 0.04) were significantly lower than Z-scores in older treated patients (11-19 years, 2 ± 1.9, n = 15). Samples from patients with Turner syndrome differed significantly from samples from untreated patients (-5.2 ± 5.1, n = 24, P = 0.003), and a Z-score of -1.7 was identified as a cut-off showing good diagnostic value for identification of patients with Turner syndrome with reduced ovarian reserve. When this cut-off was applied to other patients, analysis showed that those with indications for reduced ovarian reserve (n = 15) were significantly younger (5.9 ± 4.2 versus 10.7 ± 5.9 years, P = 0.004) and, when untreated, more often had non-malignant haematologic diseases compared with those with normal ovarian reserve (n = 24, 100% versus 19%, P = 0.009). CONCLUSION: Z-scores allow the estimation of genetic- and treatment-related effects on follicular density in cortical tissue from young patients stored for fertility preservation. Understanding the quality of cryopreserved tissue facilitates its use during patient counselling. More research is needed regarding the cytostatic effects found in this study.

The Role of Sequential BMP Signaling in Directing Human Embryonic Stem Cells to Bipotential Gonadal Cells.

Context: Human gonads arise as a pair of epithelial ridges on the surface of intermediate mesoderm (IM)-derived mesonephros. Toxic environmental factors and mutations in various genes are known to disturb normal gonadal development, but because of a lack of suitable in vitro models, detailed studies characterizing the molecular basis of the observed defects have not been performed. Objective: To establish an in vitro method for studying differentiation of bipotential gonadal progenitors by using human embryonic stem cells (hESCs) and to investigate the role of bone morphogenetic protein (BMP) in gonadal differentiation. Design: We tested 17 protocols using activin A, CHIR-99021, and varying durations of BMP-7 and the BMP inhibitor dorsomorphin. Activation of activin A, WNT, and BMP pathways was optimized to induce differentiation. Setting: Academic research laboratory. Main Outcomes Measures: Cell differentiation, gene expression, and flow cytometry. Results: The two most efficient protocols consistently upregulated IM markers LHX1, PAX2, and OSR1 at days 2 to 4 and bipotential gonadal markers EMX2, GATA4, WT1, and LHX9 at day 8 of culture. The outcome depended on the combination of the duration, concentration, and type of BMP activation and the length of WNT signaling. Adjusting any of the parameters substantially affected the requirements for other parameters. Conclusions: We have established a reproducible protocol for directed differentiation of hESCs into bipotential gonadal cells. The protocol can be used to model early gonadal development in humans and allows further differentiation to mature gonadal somatic cells.