Control of Gene Expression During the Cell Cycle and in the Developing 
Mammalian Cerebellum 
tivity of these factors is regulated during the cell 
cycle. 
Molecular Approaches Toward an 
Understanding of the Mammalian 
Cerebellum 
The mammalian cerebellum is a complex and 
highly stereotyped structure in which major pat- 
tern formation and functional organization occur 
postnatally. The precise description of the cellu- 
lar events occurring during cerebellar develop- 
ment, and the existence of many mutant mouse 
strains in which normal development of the cere- 
bellum is perturbed, recommend it as an amena- 
ble system for molecular analysis of central ner- 
vous system development. Our initial interests in 
this area have been to identify genes that are ei- 
ther essential for normal development of the cere- 
bellum or that serve as molecular markers for spe- 
cific developmental events that occur during its 
formation. Our ultimate goal is to utilize these 
genes to identify novel proteins that are crucial to 
proper development of the cerebellum and to 
identify molecular mechanisms that participate 
in specific developmental events by analysis of 
the pathways that result in their correct spatial 
and temporal expression. 
To identify genes that are required for normal 
development or maintenance of cerebellar struc- 
ture and function, we have initiated efforts to 
clone the genes responsible for several neurologi- 
cal mutants of mice. Our most significant pro- 
gress toward identification of these genes has 
been in studies concerning the Lurcher (Lc) and 
meander tail {med) loci. Lc is a semidominant 
mutation that results in death of essentially all 
cerebellar Purkinje cells, beginning at about two 
weeks of age. Secondary loss of cerebellar gran- 
ule cells and olivary neurons is also observed. We 
have constructed a detailed genetic map 
surrounding the Lc locus on chromosome 6 and 
have identified an RFLP (restriction fragment 
length polymorphism) marker approximately 
0.5 cM from the gene. Genomic sequences from 
this closely linked marker were used to screen a 
yeast artificial chromosome (YAC) library from 
Shirley Tilghman (HHMI, Princeton University), 
resulting in isolation of a 280-kilobase YAC that 
maps to chromosome 6. Using sequences isolated 
from this YAC and informative recombinants gen- 
erated during genetic mapping of the Lc locus, 
we have begun a chromosomal walk toward the 
Lc gene. 
The gene mea is a recessive mutation resulting 
in gross perturbations of cerebellar cytoarchitec- 
ture that are confined to the anterior lobes of the 
cerebellum. The sharp boundary between the 
normal and affected area of the mea /mea cere- 
bellum is reminiscent of the discrete boundaries 
evident in many Drosophila developmental mu- 
tants, suggesting that the mea gene may influ- 
ence compartmental cellular organization in 
mammalian brain. In this case we have also con- 
structed a detailed genetic map surrounding the 
mea gene on chromosome 4 and have begun ef- 
forts to identify appropriate genomic sequences 
to begin isolation of YAC clones containing the 
mea locus. The identification of genes responsi- 
ble for these and other mouse neurological muta- 
tions should provide fundamentally important 
insights into cerebellar structure and function. 
During the past year we have continued to pur- 
sue several different strategies to identify cDNA 
clones that are cell specific and developmentally 
regulated in the cerebellum. Using both subtrac- 
tive hybridization and differential screening 
methods, a large number of novel cDNA clones 
have been isolated and are presently being ana- 
lyzed. Initial results indicate that our cloning 
strategies have been successful, since many devel- 
opmentally regulated cDNAs have been identi- 
fied. For example, several candidate cDNA clones 
for the developmentally regulated neuron:glial 
ligand "astrotactin" have been obtained in a col- 
laborative effort with Mary Beth Hatten (Colum- 
bia University) . 
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