Abstract
Follicle development requires complex and coordinated interactions between both the oocyte and its associated somatic cells. In ovarian dysfunction, follicle development may be abnormal due to defective somatic cell function; for example, premature ovarian insufficiency or malignancies. Replacing defective somatic cells, using the reaggregated ovary (RO) technique, may ‘rescue’ follicle development. ROs containing mature follicles have been generated when transplanted to a host mouse to develop. We have developed a RO culture technique and the aims were to determine how follicle development differed between transplanted and cultured ROs, and the influence of ovarian age (P2 vs P6). Mouse ROs were cultured for 14 days; P2 and P6 ovaries cultured as Controls. Follicle development was compared to ROs transplanted for 14 days and ovaries from P16 and P20 mice. ROs generated from either P2 or P6 exhibited similar follicle development in culture whereas in vivo follicle development was more advanced in P6 ROs. Follicles were more developed in cultured ROs than transplanted ROs. However, follicles in cultured ROs and ovaries had smaller oocytes with fewer theca and granulosa cells than in vivo counterparts. Our results demonstrate the fluidity of follicle development despite ovary dissociation and that environment is more important to basal lamina formation and theca cell development. Furthermore, follicle development within cultured ROs appears to be independent of oocyte nest breakdown and primordial follicle formation in source ovaries. Our results highlight the need for understanding follicle development in vitro, particularly in the development of the RO technique as a potential fertility treatment.
Highlights
The development of follicles in the ovary requires complex bidirectional interactions between the somatic cells, granulosa cells (GCs) and theca cells (TCs), and the germ cells with certain steps requiring specific endocrine support
The number of trypan blue-positive dead cells in the germ cell suspension was equivalent between postnatal day 2 (P2) and P6 (P2: 2682 ± 5973; P6: 2171 ± 5520; not significant)
The total number of live cells in the germ cell suspension isolated from four mice did not differ between P2 and P6 (P2: 29506 ± 8447; P6: 36914 ± 11490; P = 0.06)
Summary
The development of follicles in the ovary requires complex bidirectional interactions between the somatic cells, granulosa cells (GCs) and theca cells (TCs), and the germ cells with certain steps requiring specific endocrine support. Ovarian tissue culture is a valuable tool for observing follicle development over time and is a potential method to develop fertilisable eggs in situations where conventional in vitro fertilisation methods are inappropriate (Eppig & O’Brien 1996, O’Brien et al 2003, Telfer et al 2008, Jin et al 2010, Morohaku et al 2016). In situations such as ovarian dysfunction or disease such as malignancy, follicle development within the ovarian tissue may be suboptimal due to defective somatic cell function. Follicle development between transplanted and cultured neonatal ROs has not been compared
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