Enzymatic activities during evolution of the cement gland in Xenopus tadpoles

Abstract

The activities of the hydrolases, a-L-fucosidase, N-acetyl-0-Dglucosaminidase (NAG), and zpacoumase appear to be involved in the regression of the cement gland in Xenopus laeuis. The involution of the gland is marked by an important rise of the total as well as the specific activities of a-L-fucosidase and zpacoumase. The specific activity of a-L-fucosidase and of zpacoumase increases about five-fold and eight-fold, respectively, after 12 days of development. Although total activity of NAG decreases during involution, its specific activity undergoes an increase of 93% after 12 days. In contrast, there is a dramatic loss in the total and specific activity of aldolase, used as a control enzyme.The behaviour of these four enzymes is strikingly different in the epidermal tissue adjacent to the gland. Their activity remains stable during the developmental period considered. These observations demonstrate that possible contamination of the explanted gland by surrounding tissue is not responsible for the observed increase in hydrolytic activity in the gland.It has been repeatedly demonstrated that lysosomal enzymes are involved in the tissue involution observed during vertebrate embryogenesis (Eeckhout, '69; Greenfield and Derby, '72; Hickey, '71; Patel, '70; Perriard, '71; Robinson, '70, '72; Scheib, '63, '77).The cement gland is an ectodermal larval organ located caudally to the mouth in most Anuran species. It secretes an abundant mucus that allows the tadpole to stick to immersed objects or the surface of the water where the oxygen tension is higher. The gland differentiates at the early neurula stage and reaches functional maturity at stage 28 (Nieuwkoop and Faber, '67). Shortly after its maturity, it involutes progressively and eventually disappears a t stage 50, about 12 days after its appearance. Regression of the gland proceeds at a precise rate and is independent of any hormonal influence (Weets and Picard, '79).Lyerla and collaborators demonstrated that the involution of the gland in Xenopus laeuis is characterized by an increased activity of lysosomal enzymes (Hsu and Lyerla, '77; Ling and Lyerla, '76). The gland in advanced regression (stage 45) had total and specific activities of acid phosphatase, P-glucuronidase, and N-acetyl-(3-D-glucosaminidase significantly greater than those observed in stage 35/36 glands. In contrast, the activity of the (3-galactosidase remained stable. The lysosomal location of these enzymes is well established in mammals. It has also been demonstrated in homogenates of total embryos and of stomachs of adult Xenopus that these enzymes have a maximal activity at an acid pH and are located in the cellular fraction sedimenting at 20,OOOg (Hsu and Lyerla, '77).The aim of the studies described in the present article was to extend our knowledge of the behaviour of different enzymes at several stages in the evolution of the gland. Cystein-proteinases and two enzymes belonging to the group of glucosidases, a-L-fucosidase and N-acetyl-(3-D-glucosaminidase, have been assayed. Develo...