Download Topic: Developmental biology Extra

Topic: Developmental biology
Extra-renal locations of tissue restricted subunits of H+ATPase
Introduction
Specialized plasma membrane multi-subunit H+ATPase pumps are present in cells of the distal
nephron, inner ear and male reproductive tract. In these specialised locations some subunits display
tissue restricted expression and replace the generic subunits. Disruptions of these specialised subunits
leads to diseases such as distal renal tubular acidosis (dRTA - a4 and B1 subunits), cutis laxa (a2) and
infantile malignant osteopetrosis (a3 subunit). Recently it has become apparent that specialised
subunits are present in a wider range of specialised membrane locations than previously thought,
adding to our knowledge of subunit combinations found throughout the body.
Objectives
To investigate novel extra-renal locations of tissue restricted H+ATPase subunits using the Atp6v0a4
knockout mouse, which is a model for recessive dRTA.
Methods
The Atp6v0a4-null line, in which a LacZ reporter cassette replaced part of the gene, was used to study
novel locations of the a4 subunit. Initially, using β-galactosidase as a reporter for the null gene, a4
expression was investigated in a range of tissues and RT-PCR was used to detect the expression of
other specialised subunits. Biochemical and histological assessments were used to assess the presence
of these subunits at protein level.
Results
The C2 and d2 subunits were identified in olfactory epithelium, which is a known location of both the
B1 and a4 subunits. The a4 subunit was found in several novel locations: the uterus of pregnant
animals; the embryonic visceral yolk sac where d2 and C2 were also identified. The presence of d2,
which has previously been identified by RT-PCR in the placenta, was confirmed at protein level. In
the male reproductive tract a4 was seen for the first time in the prostatic alveoli and the ampullary
glands as well as the previously reported epididymis and vas deferens.
Conclusion
Novel locations for the a4 subunit and other tissue-restricted subunits were elucidated, including their
presence in the visceral yolk sac, uterus and placenta and further locations of a4 and B1 were found in
the male reproductive tract. A wider knowledge of specialised subunits in the olfactory epithelium
was also gained. These studies suggest additional roles of the proton pump, indicating a further range
of homologue-specific functions for tissue-restricted subunits.