EGF‐dependent lobule formation and FGF7‐dependent stalk elongation in branching morphogenesis of mouse salivary epithelium in vitro

When supplemented with appropriate growth factors, salivary gland epithelial explants isolated from mouse embryos undergo branching morphogenesis in vitro in the absence of mesenchyme. Epidermal growth factor (EGF) induces lobule formation, while fibroblast growth factor 7 (FGF7) promotes stalk elongation. A mixture of EGF and FGF7 produces an intermediate morphology, which resembles the branching pattern of salivary epithelium observed in vivo. To investigate how lobule formation and stalk elongation are related to the pattern of epithelial cell proliferation induced by EGF and FGF7, we performed a bromodeoxyuridine labeling study in whole‐mount preparations. During the initial steps of lobule formation in EGF cultures, cleft and non‐cleft regions had similar proliferative activity. However, once clefts had fully deepened, cells with low proliferative activity appeared at the bottom of the clefts. In contrast, during stalk elongation in FGF7 cultures, distal regions of the explants always showed higher proliferative activity than proximal regions. These results suggest that stalk elongation, but not cleft formation, may result from differential cell proliferation. Dev Dyn 1999;215:148–154. © 1999 Wiley‐Liss, Inc.

[1]  H Nogawa,et al.  Substitution for mesenchyme by basement-membrane-like substratum and epidermal growth factor in inducing branching morphogenesis of mouse salivary epithelium. , 1991, Development.

[2]  B. Olwin,et al.  FGF-2: apical ectodermal ridge growth signal for chick limb development. , 1994, Science.

[3]  M. Kashimata,et al.  Epidermal growth factor system is a physiological regulator of development of the mouse fetal submandibular gland and regulates expression of the α6‐integrin subunit , 1997 .

[4]  M. Bernfield,et al.  The turnover of basal lamina glycosaminoglycan correlates with epithelial morphogenesis. , 1982, Developmental biology.

[5]  J. Boonstra,et al.  Epidermal growth factor induces rapid reorganization of the actin microfilament system in human A431 cells. , 1991, Journal of cell science.

[6]  S. Yamashina,et al.  Significant role of laminin‐1 in branching morphogenesis of mouse salivary epithelium cultured in basement membrane matrix , 1999, Development, growth & differentiation.

[7]  F. Fuller-Pace,et al.  FGF-7 (keratinocyte growth factor) expression during mouse development suggests roles in myogenesis, forebrain regionalisation and epithelial-mesenchymal interactions , 1994, Mechanisms of Development.

[8]  B. Spooner,et al.  Embryonic salivary gland epithelial branching activity is experimentally independent of epithelial expansion activity. , 1989, Developmental biology.

[9]  H. Aberle,et al.  Beta-catenin mediates the interaction of the cadherin-catenin complex with epidermal growth factor receptor , 1994, The Journal of cell biology.

[10]  J. Boonstra,et al.  The EGF receptor is an actin-binding protein , 1992, The Journal of cell biology.

[11]  J. Izpisúa-Belmonte,et al.  Involvement of FGF-8 in initiation, outgrowth and patterning of the vertebrate limb. , 1996, Development.

[12]  M. Janners,et al.  The initiation of limb bud outgrowth in the embryonic chick. , 1971, Developmental biology.

[13]  G. Goldin.  Towards a Mechanism for Morphogenesis in Epithelio-Mesenchymal Organs , 1980, The Quarterly Review of Biology.

[14]  N. K. Wessells,et al.  An analysis of salivary gland morphogenesis: role of cytoplasmic microfilaments and microtubules. , 1972, Developmental biology.

[15]  L. Wolpert,et al.  Cell Division in the Early Growth and Morphogenesis of the Chick Limb , 1970, Nature.

[16]  J. Rubin,et al.  Pattern of keratinocyte growth factor and keratinocyte growth factor receptor expression during mouse fetal development suggests a role in mediating morphogenetic mesenchymal‐epithelial interactions , 1995, Developmental dynamics : an official publication of the American Association of Anatomists.

[17]  C. Ettensohn,et al.  Mechanisms of Epithelial Invagination , 1985, The Quarterly Review of Biology.

[18]  W. Cardoso,et al.  Bud formation precedes the appearance of differential cell proliferation during branching morphogenesis of mouse lung epithelium in vitro , 1998, Developmental dynamics : an official publication of the American Association of Anatomists.

[19]  C. Tickle,et al.  FGF-4 replaces the apical ectodermal ridge and directs outgrowth and patterning of the limb , 1993, Cell.

[20]  Keiichi Yoshida,et al.  Branching Morphogenesis of Mouse Embryonic Submandibular Epithelia Cultured under Three Different Conditions , 1994, Development, growth & differentiation.

[21]  I. Thesleff,et al.  Localization and quantitation of 125I-epidermal growth factor binding in mouse embryonic tooth and other embryonic tissues at different developmental stages. , 1987, Developmental biology.

[22]  R. Keller,et al.  Regional expression, pattern and timing of convergence and extension during gastrulation of Xenopus laevis. , 1988, Development.

[23]  Y Nakanishi,et al.  Mouse embryonic submandibular gland epithelium loses its tissue integrity during early branching morphogenesis , 1996, Developmental dynamics : an official publication of the American Association of Anatomists.

[24]  S. Yamashina,et al.  Expression of Epidermal Growth Factor Receptor in Fetal Mouse Submandibular Gland Detected by a Biotinyltyramide-based Catalyzed Signal Amplification Method , 1997, The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society.

[25]  Y Nakanishi,et al.  Cell proliferation is not required for the initiation of early cleft formation in mouse embryonic submandibular epithelium in vitro. , 1987, Development.