Paracellular transport: Opening the gates for growth

CHMP4B contributes to maintaining the follicular cells integrity in the panoistic ovary of the cockroach Blattella germanica

BACKGROUND

The Endosomal Sorting Complex Required for Transport (ESCRT) is a highly conserved cellular machinery essential for many cellular functions, including transmembrane protein sorting, endosomal trafficking, and membrane scission. CHMP4B is a key component of ESCRT-III subcomplex and has been thoroughly studied in the meroistic ovaries of Drosophila melanogaster showing its relevance in maintaining this reproductive organ during the life of the fly. However, the role of the CHMP4B in the most basal panoistic ovaries remains elusive.

RESULTS

Using RNAi, we examined the function of CHMP4B in the ovary of Blattella germanica in two different physiological stages: in last instar nymphs, with proliferative follicular cells, and in vitellogenic adults when follicular cells enter in polyploidy and endoreplication. In Chmp4b-depleted specimens, the actin fibers change their distribution, appearing accumulated in the basal pole of the follicular cells, resulting in an excess of actin bundles that surround the basal ovarian follicle and modifying their shape. Depletion of Chmp4b also determines an actin accumulation in follicular cell membranes, resulting in different cell morphologies and sizes. In the end, these changes disrupt the opening of intercellular spaces between the follicular cells (patency) impeding the incorporation of yolk proteins to the growing oocyte and resulting in female sterility. In addition, the nuclei of follicular cells appeared unusually elongated, suggesting an incomplete karyokinesis.

CONCLUSIONS

These results proved CHMP4B essential in preserving the proper expression of cytoskeleton proteins vital for basal ovarian follicle growth and maturation and for yolk protein incorporation. Moreover, the correct distribution of actin fibers in the basal ovarian follicle emerged as a critical factor for the successful completion of ovulation and oviposition.

SIGNIFICANCE

The overall results, obtained in two different proliferative stages, suggest that the requirement of CHMP4B in B. germanica follicular epithelium is not related to the proliferative stage of the tissue.

Premature endocycling of Drosophila follicle cells causes pleiotropic defects in oogenesis

Endocycling cells grow and repeatedly duplicate their genome without dividing. Cells switch from mitotic cycles to endocycles in response to developmental signals during the growth of specific tissues in a wide range of organisms. The purpose of switching to endocycles, however, remains unclear in many tissues. Additionally, cells can switch to endocycles in response to conditional signals, which can have beneficial or pathological effects on tissues. However, the impact of these unscheduled endocycles on development is underexplored. Here, we use Drosophila ovarian somatic follicle cells as a model to examine the impact of unscheduled endocycles on tissue growth and function. Follicle cells normally switch to endocycles at mid-oogenesis. Inducing follicle cells to prematurely switch to endocycles resulted in the lethality of the resulting embryos. Analysis of ovaries with premature follicle cell endocycles revealed aberrant follicular epithelial structure and pleiotropic defects in oocyte growth, developmental gene amplification, and the migration of a special set of follicle cells known as border cells. Overall, these findings reveal how unscheduled endocycles can disrupt tissue growth and function to cause aberrant development.

Premature endocycling of Drosophila follicle cells causes pleiotropic defects in oogenesis

Endocycling cells grow and repeatedly duplicate their genome without dividing. Cells switch from mitotic cycles to endocycles in response to developmental signals during the growth of specific tissues in a wide range of organisms. The purpose of switching to endocycles, however, remains unclear in many tissues. Additionally, cells can switch to endocycles in response to conditional signals, which can have beneficial or pathological effects on tissues. However, the impact of these unscheduled endocycles on development is underexplored. Here, we use Drosophila ovarian somatic follicle cells as a model to examine the impact of unscheduled endocycles on tissue growth and function. Follicle cells normally switch to endocycles at mid-oogenesis. Inducing follicle cells to prematurely switch to endocycles resulted in lethality of the resulting embryos. Analysis of ovaries with premature follicle cell endocycles revealed aberrant follicular epithelial structure and pleiotropic defects in oocyte growth, developmental gene amplification, and the migration of a special set of follicle cells known as border cells. Overall, these findings reveal how unscheduled endocycles can disrupt tissue growth and function to cause aberrant development.