Gene structure and map location of the murine homolog of the
Huntington-associated protein, Hap1
* K. Duan,
Department of Medical Genetics, University of British Columbia, Vancouver, V6T 1Z4, Canada.
Laboratory of Molecular Neurobiology, Departments of Psychiatry and Neuroscience, Johns Hopkins University School of Medicine,
Baltimore, Maryland 21205, USA.
Department of Pathology, University of Washington, Seattle, Washington, USA.
Abstract. Huntington’s Disease (HD) is an inherited progressive
neurodegenerative disorder associated with a mutation in a gene
expressed in both affected and non-affected tissues. The selective
neuropathology in HD is thought to be mediated in part through
interactions with other proteins including the Huntington Associ-
ated Protein, HAP-1, which is predominantly expressed in the
brain. We have mapped its murine homolog, Hap1, to mouse Chr
11 (band D), which shares extensive synteny with human Chr 17
including the region 17q21–q22, where the gene for ‘frontotem-
poral dementia and parkinsonism linked to chromosome 17’ has
bee mapped. In addition, we have sequenced a 21,984 base pair
(bp) genomic clone encompassing the entire Hap1 gene. It is or-
ganized as 11 exons and flanked by exons from potentially one or
more novel genes. At least three Hap1 transcripts (Hap1-A; Hap1-
B; Hap1-C) can be formed by alternative splicing at the 3Ј end of
the gene leading to protein isoforms with novel C-termini.
Huntington’s Disease (HD) is a progressive neurodegenerative dis-
order with insidious onset usually in adulthood, which culminates
in death typically within 15–20 years (Hayden 1981). In the initial
stages, it often manifests itself with personality changes, clumsi-
ness, or chorea, which progresses to severe incoordination, rigid-
ity, and dementia. These changes are accompanied by progressive
loss of medium spiny neurons within the caudate and putamen
(which together constitute the striatum), and in deep layers of the
The cloning of the HD gene revealed the presence of a poly-
morphic CAG repeat tract within the first exon encoding polyglu-
tamines (HDCRG, 1993). The number of glutamine repeats varies
from 8 to 35 individuals not affected with HD (Rubinsztein et al.
1996; Brinkman et al. 1997). However, individuals with signs and
symptoms of HD have CAG repeat lengths of 36 or more (Kremer
et al. 1994; Rubinsztein et al. 1996; Brinkman et al. 1997). There
is also an inverse correlation between CAG repeat length and
severity of disease, such that very long repeats are associated with
an earlier age of onset and increased severity (Andrew et al. 1993).
At least six other neurodegenerative conditions are also caused by
polyglutamine repeat expansions within their respective genes (see
Mandel 1997; Ross et al. 1998). All of these disorders are believed
to involve a ‘gain of function’ mechanism.
The genes associated with polyglutamine repeat disorders are
generally widely expressed, yet lead to highly selective patterns of
neurodegeneration (Ross 1995). For example, gene products asso-
ciated with HD and spinocerebellar ataxia type 1 (SCA1) are both
widely expressed but lead to very divergent neuropathology. In
HD, the cerebellum is relatively unaffected, yet it is the principal
site of pathology in spinocerebellar ataxia type 1 (SCA1). These
highly selective patterns of neurodegeneration could potentially be
mediated through interactions with proteins with a more restricted
pattern of expression.
In the case of HD, several interacting proteins have been iden-
tified, including the Huntington Associated Protein (HAP-1), ubiq-
uitin conjugating enzyme (hE2-25K), glyceraldehyde-3-phosphate
dehydrogenase (GAPDH), and Huntington Interacting Protein
(HIP-1) (Li et al., 1995; Kalchman et al. 1996, 1997; Burke et al.
1996; Wanker et al. 1997).
We previously cloned the cDNA from the rat HAP-1 gene
(rHAP-1), using an N-terminal fragment of the HD protein con-
taining 44 glutamine repeats, in a yeast two-hybrid screen of a rat
brain cDNA library (Li et al. 1995). Two distinct rat HAP-1 cD-
NAs were identified, rHAP1-A (3708 bp) and rHAP1-B (3201 bp),
differing only with respect to their 3Ј ends, presumably as a result
of alternative splicing (Li et al. 1995). HAP-1 is predominantly
expressed in the brain and shows an increased interaction with the
mutant HD protein (Li et al. 1995, 1996). We have recently re-
ported that HAP-1 also interacts with Duo, a Trio-like protein with
a rac1 guanine nucleotide exchange factor domain (Colomer et al.
1997), and with the p150 glued component of dynactin. These
proteins are also enriched in the brain.
To further illuminate our understanding of HAP-1, we initiated
a study to determine its genomic localization and genomic orga-
nization in mice. Here, we describe the cloning and sequencing of
a 21,984-bp genomic clone encompassing the murine HAP-1 gene
(Hap1), as well as its map position. Hap1 maps to Chr 11 (band D)
and consists of 11 exons. Splice events in the 3Ј end of this gene
are capable of generating at least three transcripts. In addition, the
genomic sequence encompasses exons from one or more poten-
tially novel gene(s).
Materials and methods
Library screening and sequencing.
A phage genomic library (Strata-
gene), derived from a 129/SvJ mouse strain, was screened with a rat HAP-1
cDNA probe (PC43), corresponding to position 866 to 1372 of the pub-
lished rHAP-1 cDNA sequence (Li et al. 1995). Hybridizations were per-
formed in 50% formamide and 6 × SSC (see Sambrook et al. 1989) at
42°C. Sequencing was carried out on an Applied Biosystems (ABI) auto-
mated sequencer with dye-labeled primers. The sequence was assembled
with the Sequencher software.
Present address: Human Genetics Unit, Molecular Medicine Centre, West-
ern General Hospital, Edinburgh, EH4 2XU, UK.
Correspondence to: M.R. Hayden
The nucleotide sequence data reported in this paper have been submitted to
GenBank and have been assigned the accession number AJ003128.
Mammalian Genome 9, 565–570 (1998).
© Springer-Verlag New York Inc. 1998