Diversification of follicular cells in the ovaries of the horse fly Haematopota italica (Diptera: Tabanidae) : similarities and differences with the Drosophila model system

In insect ovaries, germ line cells are surrounded by somatic cells that initially form a uniform follicular epithelium. The subsequent diversification of the follicular cells into several subpopulations enables specification of distinct structures in different regions of complex eggshells. It also influences the patterning of the future embryo. These processes have been extensively studied at both the cellular and molecular levels using the Drosophila ovary as a model system. It is not clear however, to what extent the Drosophila model of the follicular epithelium patterning is universal for the entire Diptera group. Here, we analyze the diversification of the follicular cells in a distant Drosophila relative, the horse fly, Haematopota italica. We found that in this species, there are 6 recognizably different follicular cell subpopulations within the previtellogenic ovarian follicles. Ultrastructural analysis of the follicular epithelium revealed two morphologically distinct clusters of follicular cells residing at the anterior and posterior poles of the follicles. Each cluster consists of 2-3 polar cells located centrally and surrounded by several outer cells called border cells (at the anterior pole) or border-like cells (at the posterior pole). During previtellogenesis, the clusters lose the initial symmetry as their cells differentiate and develop conspicuous cytoplasmic projections comprising cytoskeletal elements. Ultimately, the follicular cells of the anterior and posterior clusters become morphologically different and, as we suggest, participate in different processes during oogenesis and formation of the eggshell in H. italica

Unusual morphological adaptations and processes associated with viviparity in an epizoic dermapteran

Matrotrophic viviparity is a reproductive pattern in which offspring develop inside a female's body which provides gas exchange and nutrients necessary for development. Besides placental mammals, structural and physiological aspects of matrotrophic viviparity are poorly characterized. In insects, the majority of species is oviparous, i.e. lay eggs, and viviparous reproduction has been reported only in 11 out of 44 orders, including earwigs (Dermaptera). Among dermapterans, matrotrophic viviparity has been reported in two epizoic subgroups: Arixeniidae and Hemimeridae. Here, we provide morphological evidence for distinct adaptations for this mode of viviparity in embryonic and maternal tissues in a representative of the latter subgroup, Hemimerus talpoides. Our study reveals a novel mechanism of maternal contribution to embryonic development which operates during oogenesis and involves characteristic modification of endoplasmic reticulum cisternae. Conspicuous and apparently inactive para-crystalline stacks of the endoplasmic reticulum are deposited in the oocyte cytoplasm and become activated during early embryonic development. Our analyses indicate additionally that in Hemimerus, transformed follicular/ovarian cells (on the mother's side) and an evagination of the dorsal vessel (on the embryo's side) converge to form a cephalic vesicle, structure analogous to a placenta. The cellular architecture of this unusual "cephalic placenta" points to its participation in an exchange of low molecular weight substances between a mother and developing embryo