Due to their property to bind to phospholipids in a Ca2 +-dependent manner, proteins of the annexin superfamily are involved in many membrane-related events and thus in various forms of physiological and pathological processes. We were therefore interested in analyzing the mRNA expression of the annexins in the severely disorganized pituitaries of the athyroid Pax8−/− mice in comparison with that of control animals. In neither condition was mRNA expression of the annexins A3, A7, A8, A9, A11, and A13 detectable. The annexins A2, A4, and A6 were equally expressed in wild-type and Pax8−/− mice. Transcript levels of A1 and A10 were highly increased and those of A5 were significantly decreased in the athyroid mutants compared with controls. Treatment of Pax8−/− mice with physiological doses of thyroxine for 3 days normalized the mRNA expression of A1, A5, and A10 indicating that the expression of these annexins is directly regulated by thyroid hormone (TH). Since A5 exhibits by far the highest transcript levels of all annexins in the pituitary and its regulation by TH could be also confirmed at the protein level, we analyzed the mRNA expression of pituitary hormones in A5−/− mice. In these mutants, only the β-FSH mRNA expression was found to be significantly reduced, while the mRNA expression levels of the other pituitary hormones were not altered. These results support the concept that annexins might serve important albeit redundant functions as modulators of pituitary hormone secretion.
Jens Mittag, Wiebke Oehr, Heike Heuer, Tuula Hämäläinen, Bent Brachvogel, Ernst Pöschl and Karl Bauer
Joachim Wistuba, Jens Mittag, C Marc Luetjens, Trevor G Cooper, Ching-Hei Yeung, Eberhard Nieschlag and Karl Bauer
Severe forms of congenital hypothyroidism lead to serious clinical symptoms if thyroid hormone replacement therapy is not instituted immediately after birth. In this study, Pax8−/− mice that are born without a thyroid gland were used as an animal model to study the consequences of congenital hypothyroidism. As expected, adequate treatment of these animals with thyroxine restored the general deficits of congenital hypothyroidism; however, Pax8-deficient male mice were infertile. We report here that in these mice, the efferent ducts and epididymides are either absent or the efferent ducts exhibit a reduced lumen and extensive connective tissue, which appears to impair testicular drainage and subsequently leads to complete absence of spermatozoa from the epididymis. The results suggest that, starting with the onset of pubertal testicular fluid secretion, a backpressure is created in the testis by the absence of efferent ducts or constriction of their tubule lumen when present. This subsequently leads to secondary disorganization of the seminiferous epithelium that increases with age, resulting in mixed atrophy of the testis in the adult. Serum testosterone levels as well as mRNA expression of anterior pituitary hormones are in the normal range, indicating that the observed infertility is not due to hormonal imbalance, but rather to a developmental defect of the efferent ducts. The demonstration of Pax8 expression in the epithelia of the epididymis and the efferent ducts suggests a direct morphogenic role of Pax8 in the development of these organs. It remains to be elucidated whether congenital hypothyroid male patients with mutations in the Pax8 gene are similarly affected.