Degeneration of germ line cells in amphibian ovary Maria Ogielska, Beata Rozenblut, Renata Augustyn ´ ska and Agnieszka Kotusz Department of Biology and Conservation of Vertebrates, Zoological Institute, University of Wroclaw, ul. Sienkiewicza 21, 50-335 Wroclaw, Poland Keywords: oogenesis, amphibians, germ line, ovary, atresia Accepted for publication: 8 June 2009 Abstract Ogielska, M., Rozenblut, B., Augustyn ´ ska, R., Kotusz, A. 2010. Degeneration of germ line cells in amphibian ovary. — Acta Zoologica (Stockholm) 91: 319–327 We studied the morphology of degenerating ovarian follicles in juvenile and adult frogs Rana temporaria, Rana lessonae and Rana ridibunda. Degeneration of primordial germ cells was never observed and was extremely rare in oogonia and early oocytes in a cyst phase in juveniles. Previtellogenic oocytes were rarely affected. Three main types of atresia were identified. In type I (subdivided into stages A–D), vitellogenic oocytes are digested by proliferating follicle cells that hypertrophy and become phagocytic. A – germinal vesicle shrinks, nucleoli fuse, oocyte envelope interrupts, and follicular cells hypertrophy; B – follicular cells multiply and invade the oocyte; C – entire vesicle is filled by phagocytic cells; D – degenerating phagocytes accumulate black pigment. Type II is rare and resembles breakdown of follicles and release of ooplasm. In type III, observed in previtellogenic and early vitellogenic oocytes, ooplasm and germinal vesicle shrink, follicle cells do not invade the vesicle, and condensed ooplasm becomes fragmented. The residual oogonia in adult ovaries (germ patches) multiply, but soon degenerate. Maria Ogielska, Department of Biology and Conservation of Vertebrates, Zoo- logical Institute, University of Wroclaw, ul. Sienkiewicza 21, 50-335 Wroclaw, Poland. E-mail: ogielska@biol.uni.wroc.pl Introduction Oocyte degeneration inside their follicles has been reported in vertebrate ovaries for a long time. The process by which oo- cytes are eliminated before ovulation is often called intrafollic- ular atresia. In mammals, which are the best studied group in this respect, the process of degeneration of germ cells is divided into two phases. The early phase, which is called attri- tion, takes place before birth and affects only germ cells before folliculogenesis. The late phase, in which degeneration of fol- licular cells precedes the death of oocytes, is called atresia and occurs between puberty and menopause. Recent studies revealed that degeneration of follicles is in fact a result of pro- grammed cell death, mainly apoptosis (for review see Hsueh et al. 1994; Matova and Cooley 2001; Baum et al. 2005). In fishes and amphibians, the term atresia is referred to degener- ation of the follicles and is still in use as a synonym of degener- ation and resorption of oocytes that are not ovulated (Khoo 1974; Hunter and Macewicz 1985; Kulkarni and Pancharatna 1996; Miranda et al. 1999). To our knowledge, no conclusive studies exist that summa- rizes the patterns of physiological germ cell death in anuran ovaries during their differentiation and development, although gonads of many anuran species have been described during the last years (for literature see Ogielska and Kotusz 2004; Ogielska and Bartman ´ska 2009). The aim of this study was a detailed description of morphological changes in degenerating germ line cells together with accompanying somatic cells (pre- follicular and follicular cells, and theca) in developing ovaries with reference to the age of the female. We paid attention to all stages of germ line cells present in an ovary at successive stages of its differentiation. Our observations that were made from early tadpole stages to sexual maturity allowed us to describe the morphology of degenerating germ line cells throughout the entire oogenesis. Special attention was paid to the juvenile period when atrectic follicles were numerous. Materials and Methods Tadpoles, juveniles, and adult females belonging to three species of the family Ranidae, namely Rana temporaria, Rana lessonae and Rana ridibunda, were used. The tadpoles of each species were kept separately under natural light and tempera- ture conditions. At Gosner (1960) stage 25 (beginning to Acta Zoologica (Stockholm) 91: 319–327 (July 2010) doi: 10.1111/j.1463-6395.2009.00411.x Ó 2009 The Authors Journal compilation Ó 2009 The Royal Swedish Academy of Sciences 319