able for studying integrin functions in a genetically 
accessible organism. 
Dr. Reichardt is also Professor of Physiology 
and of Biochemistry and Biophysics at the Univer- 
sity of California, San Francisco. 
Books and Chapters of Books 
Reichardt, L.F., and Tomaselli, K.J. 1991 . Regula- 
tion of neural development by the extracellular 
matrix. In Receptors for Extracellular Matrix 
(McDonald, J.A., and Mecham, R.P., Eds.). San 
Diego, CA: Academic, pp 157-193. 
Articles 
Bossy, B., Bossy Wetzel, E., and Reichardt, L.F. 
1991. Characterization of the integrin cvg subunit: 
a new integrin -associated subunit, which is 
prominently expressed on axons and on cells in 
contact with basal laminae in chick embryos. 
£MBO/ 10:2375-2385. 
Neugebauer, K.M., Venstrom, K.A., and Rei- 
chardt, L.F. 1992. Adhesion of a chicken myelo- 
blast cell line to fibrinogen and vitronectin 
through a /3j -class integrin. / Cell Biol 1 16:809- 
815. 
Reichardt, L.F., and McMahon, U.J. 1 99 1 . Cell biol- 
ogy of neurons and glia. Curr Opin Neurobiol 
1:337-338. 
MOLECULAR MECHANISMS OF DEVELOPMENTAL AND REGULATED EXPRESSION 
OF NEUROENDOCRINE GENES 
Michael G. Rosenfeld, M.D., Investigator 
Molecular Mechanisms of Anterior Pituitary 
Gland Development 
Defining the mechanisms by which specialized 
cells arise and generate organs containing function- 
ally diverse cell types is a fundamentally important 
issue in understanding development. Therefore a 
major research focus in the laboratory has been to 
define the molecular mechanisms that dictate the 
developmental and regulated expression of neuro- 
endocrine genes and to begin to apply these princi- 
ples to analysis of neuronal gene expression. Dr. Ro- 
senfeld and his colleagues have initially utilized the 
anterior pituitary as a model for understanding the 
molecular mechanisms involved in generating spe- 
cific cell phenotypes within an organ. 
Rathke's pouch, the pituitary precursor, becomes 
committed to specific organ development several 
days before the expression of markers of individual 
cell types within the mature gland. Between the 
time of organ commitment and organ maturation, a 
series of cell-type-specific differentiation and prolif- 
eration events occur, generating five cell types in 
the mature anterior pituitary gland defined by the 
trophic factors that they synthesize and secrete. The 
anterior pituitary arises from ectodermal cells adja- 
cent to the anterior neuropore that involute to make 
contact with the neuroectoderm that gives rise to 
the hypothalamus. This contact is the only region of 
mesodermal incompetence between ectoderm and 
neuroectoderm in the primitive head, enabling the 
resultant cell-cell contact to serve as the critical in- 
ductive event. Coincident with these cell-cell con- 
tacts on embryonic day 11 (Ell) in the rat. Dr. 
Rosenfeld and his colleagues found that the first 
known anterior pituitary marker, the a-glycoprotein 
subunit transcript, is restricted to most or all cells in 
a single layer of epithelium in a clear posterior- 
anterior gradient, suggesting an asymmetry of the 
inducing factor(s). 
A fundamental issue is whether cells that might 
fail to express the a-glycoprotein subunit marker at 
this stage can serve as precursors of specific cell 
types. Because the five cell types subsequently arise 
in a precise temporal and spatial pattern, the signals 
that trigger the appearance of each cell type from 
the apparently homogeneous primordium remain a 
question. While individual cell types arise in a strati- 
fied fashion in the developing gland, the five mature 
cell types are more homogeneously distributed 
throughout the anterior pituitary. This could reflect 
either a loss of homophilic interactions between 
cell types or the action of migration-inducing fac- 
tors. The initial appearance of differentiated cell 
types within restricted portions of the anterior pitu- 
itary may indicate that specific signals induce pro- 
genitor cells to differentiate or proliferate agents 
from other tissues or the pituitary itself. Cortico- 
trophs and thyrotrophs arise on El 4, with gonado- 
trophs arising on El 7. Although the structurally re- 
lated prolactin and growth hormone genes are 
ultimately expressed in discrete cell types (lacto- 
trophs and somatotrophs, respectively) , their initial 
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