Cell Biology Section, School of Biology, University of La Laguna, Tenerife, Spain Origin of Adenohypophysial Lobes and Cells from RathkeÕs Pouch in Chicken (Gallus gallus) and Japanese Quail (Coturniz coturniz japonica). Expression of Calcium-Binding Proteins R. Reyes 1 * , M. Gonza ´lez 1,2 and A. R. Bello 1 1 Cell Biology Section, School of Biology, University of La Laguna, 38206, Avda. Astrofı´sico Fco, Sa´nchez s/n, La Laguna, Tenerife, Spain; 2 Department of Physiology, School of Medicine and Institute of Biomedical Technologies, University of La Laguna, Tenerife, Spain; *Corresponding author: Tel.: +34 22 31 84 17; fax: +34 22 31 83 11; e-mail: rreyes7@hotmail.com With 4 figures and 1 table Received December 2006; accepted for publication July 2007 Summary A histological and immunochemical study of adenohypophysis development in two bird species: chicken (Gallus gallus) and Japanese quail (Coturnix coturnix japonica) was carried out, focussing firstly morphologically on the origin of its different lobes, then secondly on the differentiation of hormone-pro- ducing cells from the adenohypophysial anlage and their involvement in the differentiation of three calcium-binding proteins. The results of the morphological development study show how the origin of the adenohypophysis in chicken is totally ectodermic, whilst in Japanese quail the endoderm, in the form of SesselÕs pouch, participates in forming the rostral zone of the anterior lobe. After studying the organogenesis and spatio/temporal differentiation of the hormone-producing cells proceeding from the adenohypophysial anlage, a regionaliza- tion model is proposed for the origin of the different lobes and cell types as well as time sequence, fundamentally the origin of cell regionalization in the adult adenohypophysis. In this process, at least in the two bird species studied, the results obtained from expressing the calcium-binding proteins, cal- bindin D 28K, calretinin and parvalbumin show a character- istic distribution pattern for each, suggesting distinct functions. Introduction Situated at the base of the hypothalamus, the hypophysis is a complex gland, which is crucial for the maintenance of several homoeostatic functions like growth, metabolism or reproduc- tion. The degree of development of the different lobes of the adenohypophysis and the distribution of glandular cells in the anterior lobe (AL) varies between mammals and non-mam- malian vertebrates. The origin of these differences is easily demonstrable by embryonic development studies, at the structural level and that of differentiation of hormone- producing cells. Several studies have focussed on the differentiation in time of the different hormones in different vertebrate groups, examining cell regionalization in non-mammalian vertebrates (Schreibman and Margolis-Kazan, 1979; Pearson et al., 1983; Batista et al., 1989). These authors have shown in teleost and in different reptile species, turtles and lizards, that this regionalization pattern departs from RathkeÕs pouch (RP). This process has not previously been studied in birds except in gonadotropic cells (Maseki et al., 2004). Within the vertebrates, the birds presents the greatest controversies related to the time sequence of hormone differ- entiation (Gasc and Sar, 1981; Thommes et al., 1987; Kansaku et al., 1994). These also arise for the results of a single species; for example in the chicken (Gallus gallus) some authors describe different stages in the differentiation of somatotropic (Gasc and Sar, 1981; Thommes et al., 1987; Malamed et al., 1993; Porter et al., 1995; Kansaku et al., 1994; Allaerts et al., 1999), lacto- tropic (Gasc and Sar, 1981; Barabanov, 1985; Ishida et al., 1991; Kansaku et al., 1994; Woods and Porter, 1998; Allaerts et al., 1999) and gonadotropic cells (Gasc and Sar, 1981; Kansaku et al., 1994; Allaerts et al., 1999; Puebla-Osorio et al., 2002; Maseki et al., 2004). Transcription factors are involved in the differentiation of adenohypophysial glandular cells, which can be calcium dependent given the specific expression of different calcium- binding proteins during development; this has only been studied in mammals (Perrone et al., 1999). In this work our purpose was to study adenohypophysis development in two birds species, focussing on the origin in RP of each lobe, the origin and differentiation sequence of the different hormone-producing cells, and the involvement of different calcium-binding proteins in the process. Material and Methods Animals Chickens and Japanese quails at different embryonic and post- natal stages were used. The eggs were incubated at 38°C with an environmental humidity between 45% and 75%. All efforts were made to minimize animal suffering and to reduce the number used. They were anaesthetized and killed in accor- dance with the European Communities Council Directive of 24 November 1996 (86/609/EEC). Antisera and antibodies Antisera were developed in rabbit against adrenocorticotropic hormone (ACTH) (1-24), beta-endorphin (bEND), alpha- melanocyte stimulating hormone (aMSH), hb thyroid  Present address: Cell Metabolism Institute, C/Manuel de Falla 15, La Laguna 38208, Tenerife, Canary Islands, Spain. Ó 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag www.blackwell-synergy.com Anat. Histol. Embryol. 37, 272–278 (2008) doi: 10.1111/j.1439-0264.2007.00840.x ISSN 0340–2096