Identification of a novel myosin-Va mutation in an ataxic mutant
Graduate School of Human Informatics, Nagoya University, Nagoya 464-8601, Japan
Department of Teratology and Genetics, Research Institute of Environmental Medicine, Nagoya University, Nagoya 464-8601, Japan
Department of Endocrinology and Metabolism, Research Institute of Environmental Medicine, Nagoya University, Nagoya 464-8601, Japan
Laboratory of Animal Management, School of Agricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
School of Information and Science, Nagoya University, Nagoya 464-8601, Japan
Received: 20 January 2000 / Accepted: 16 March 2000
Abstract. Mutations of the myosin-Va gene (Myo5a) cause di-
luted coat color in mice and are occasionally associated with se-
vere neurological disorders. Dilute-opisthotonus (dop) is a spon-
taneous gene mutation in the rat, and phenotypes of the homozy-
gote (dop/dop) are similar to those of the Myo5a-deficient mouse,
suggesting that the mutation resides in the rat Myo5a gene. To
elucidate the molecular basis of the dop mutation, we cloned the
rat Myo5a cDNA from the wild type and the dop/dop. The wild-
type rat Myo5a cDNA contained a 5487-bp ORF and showed
higher homology with Myo5a of the other species than Myr6
(Myo5b) in the rat. A 141-bp in-frame deletion was detected in the
head region in the dop cDNA. An intragenic rearrangement con-
sisting of a 306-bp inversion associated with 17-bp and 217-bp
deletions were identified in the Myo5a gene of the dop genome.
This rearrangement involved a 141-bp exon, which was skipped in
the dop transcript. The MyoVA protein expression was severely
impaired in the dop/dop brain. This is the first report to define the
dop mutation as the Myo5a gene abnormality in the rat.
Numerous gene mutations associated with neurologic disorders
have been reported in mice but are less known in rats. Previously
we reported a rat mutant, dilute-opisthotonus (dop), that arose
spontaneously and is inherited in an autosomal recessive manner.
The dop homozygotes (dop/dop) show diluted coat color and
ataxic behavior around 12 days after birth. They develop convul-
sive limb movement, opisthotonus, body weight loss, and weak-
ness approximately 3 weeks after birth, and die, presumably owing
to inability of food intake (Dekker-Ohno et al. 1993).
Linkage analysis with PCR-amplified microsatellite markers
mapped the dop gene to a locus on rat Chr 8, which was syntenic
with the dilute gene locus on mouse Chr 9 (Ohno et al. 1996). The
molecular analysis of the mouse dilute cDNA revealed that the
gene encodes Myosin-Va (MyoVA) (Mercer et al. 1991). More
than 200 spontaneous, chemical- and radiation-induced mutations
have been identified at the mouse dilute/myosin-Va gene (Myo5a)
locus. Also, homozygotes of lethal dilute alleles, dilute-lethal (d
) and dilute-lethal20J (d
), show similar phenotypes as
the dop/dop, e.g., diluted coat color and neurological disorders,
and die approximately 3 weeks after birth (Searle 1952). The re-
sponsible gene mutation of the d
was identified as a ge-
nomic deletion in the Myo5a, resulting in a markedly reduced
expression level of the transcripts and complete absence of the
MyoVA protein (Bridgman 1999; Evans et al. 1997; Moore et al.
1988; Strobel et al. 1990). The molecular dissection of 17 viable
dilute alleles, which show milder phenotypes of the d
identified Myo5a gene mutations (Huang et al. 1998a, 1998b). In
humans, patients with the Griscelli disease who have mutations on
the MYH 12 (the human homolog of the Myo5a) showed silvery
hair color, neurologic defects, and variable cellular immunodefi-
ciency (Engle and Kennett 1994; Moore et al. 1995; Pastural et al.
1997). Taken together, these findings strongly suggest that the dop
mutation resides in the Myo5a gene in the rat.
MyoVA is a member of the unconventional myosin family that
has been identified in many non-muscle tissues of vertebrates and
invertebrates and has been classified according to the primary
structures (Hasson and Mooseker 1997; Mermall et al. 1998).
Class V myosins, including the mouse MyoVA, consist of the
-terminal actin-binding “head” domain, the “neck” domain,
and the COOH-terminal “tail” domain. MyoVA has been thought
to function as an actin-dependent organelle transporter (Cheney et
al. 1993; Mermall et al. 1998; Langford and Molyneaux 1998;
Huang et al. 1999). Studies using d
mouse melanocytes indi-
cated that MyoVA is critical for melanosome transport and that the
defect is responsible for the diluted coat color. In neurons, MyoVA
has been suggested to play a role for a variety of neuronal func-
tions (Prekeris and Terrian 1997; Wang et al. 1996; Evans et al.
1997; Tabb et al. 1998; Bridgman 1999). Electron microscopic
Correspondence to: Y. Hayashi, E-mail: firstname.lastname@example.org
Fig. 1. Northern blot analysis of the brain poly (A)+ RNA from the control
(lane c) and the dop/dop (lane d). The membrane was hybridized with a
mouse Myo5a cDNA clone, C23, or the mouse glycerol-3-aldehyde phos-
phate dehydrogenase (GAPDH) cDNA as a probe. Arrowheads indicate
three major transcripts hybridized with C23. The positions of 28S and 18S
ribosomal RNAs are indicated.
Mammalian Genome 11, 649–655 (2000).
© Springer-Verlag New York Inc. 2000