Is abnormal limb bud morphology in the mutant talpid2 chick embryo a result of altered intercellular adhesion? Studies employing cell sorting and fragment fusion

Reprinted from THE JOURNAL or EXPERIMENTAL ZOOLOGY Vol. 181, No. 1, July 1972 © The Wistar Institute Press 1972 Is Abnormal Limb Bud Morphology in the Mutant Talpidz Chick Embryo a Result of Altered lntercellular Adhesion? Studies Employing Cell Sorting and Fragment Fusion RICHARD NIEDERMAN 1 AND PETER B. ARMSTRONG Department of Zoology, The University of California, Davis, California 95616 ABSTRACT In the past, studies of avian limb morphogenesis emphasized epithelial-mesenchymal tissue interactions and problems of determination of limb symmetry. In contrast, a recent hypothesis, based on studies of the ag- gregation rates of dissociated cells and on computer modeling, proposes that the paddle shaped polydactylous limb of the talpid3 mutant is the result of in- creased intercellular adhesion of limb bud mesoderm ceHs during limb develop- ment. The notion that differences in intercellular adhesion may have profound effects on limb morphogenesis has not been critically explored previously. The present experimental approach includes studies of cell sorting in aggre- gates containing both talpid? and wild-type cells. In this system, adhesive differences should result in cell sorting. Instead, cell sorting did not occur, indi- cating by this test at least, that limb bud mesoderm cells of talpid? and wild-type embryos are equally adhesive. This conclusion ﬁnds support from studies involv- ing tissue spreading in fused fragments of talpid? and wild-type limb bud mesenchyme tissue and in studies of kinetics of aggregation of dissociated cells. The developing avian limb is one of the most extensively studied morphogenetic systems in higher organisms (see for re- view: Zwilling, ’61; Amprino, ’65; Goet- inck, ’66; Saunders and Gasseling, ’68). The use of genetic mutants in the study of avian limb development has provided important information for the study of normal limb development (see for review: Abbott, ’67). A particularly interesting example of this is the work of Ede and his co-workers with the talpid-7 mutant, which has paddle-shaped polydactylous limbs. The initial defect produced in the limb by the talpid3 allele occurs in the mesoderm and apparently affects mesen- chymal cell movement and coalescence (Ede and Kelly, ’64a,b). Ede has proposed that the talpid locus has its effect pri- marily on the adhesive properties of limb bud mesenchymal cells, with the talpid3 allele resulting in limb mesodermal cells which are more strongly adhesive than corresponding cells of wild-type embryos (Ede and Agerbak, ’68). This hypothesis is of considerable interest because until now, most of the interest in avian limb J. EXP. ZooL., 181: 17-32. morphogenesis has centered about prob- lems of morphogenetic cell death (Saun- ders, ’66) and tissue-tissue interactions (i.e., the initial induction of apical ecto- dermal ridge formation by underlying pre- sumptive limb mesoderm (Saunders, ’48; Balinsky, ’56, ’57); stimulation of mitosis (Searls, ’65) and outgrowth (Saunders, ’48; Zwilling, ’49, ’55, 56a,b,c,d) of distal limb bud mesoderm by the apical ectoder— mal ridge; and the role of limb bud meso- derm in the determination of placement and maintenance of the apical ectodermal ridge (Saunders, ’49; Zwilling, ’56d, ’64; Zilling and Hansborough, ’56)). Ede has introduced the problem of adhesive inter- action between limb bud mesodermal cells into the general problem of limb morpho- genesis. In experimental attempts to determine the validity of his hypothesis, Ede has demonstrated that trypsin-dissociated tal- pid3 limb bud mesodermal cells aggregate 1 Present address: Harvard School of Dental Medicine, 188 Longwood Avenue, Boston, Massachusetts 02115. Requests for reprints should be addressed to Mr. Armstrong. 17