DR STACIA SOWER
Understanding
lamprey
reproduction
Can you summarise the focus and objectives
of your research?
The major goal of my current research has been
to test the global hypothesis that lamprey have
a hypothalamic-pituitary-gonadal axis. The
specific objectives of our GnRH receptor work
are to characterise:
• Lamprey GnRHR-2 and 3 sequences and
perform phylogenetic analysis to determine
function in second messenger activation assays
and ligand-binding specificity
• Key functional features of lamprey GnRH
receptor-1, 2 or 3 (type-II receptors) by sitedirected mutagenic studies
• Differential signalling properties and the
mechanisms of the termination of the
intracellular signalling attributable to the
C-terminal tail of lamprey GnRH receptor-1, 2
or 3 by using transient cell lines that express
either full-length or point mutants
What, specifically, do you anticipate will be
the key outcomes of your research?
Identification and functional studies of novel
GnRH receptors from basal vertebrates can
provide valuable information on the complexity
and molecular delineation of the interactions
of GnRHs and their respective receptors, and
provide considerable insight and clarification
into the molecular basis for transmission of
the signal to the G protein or other signalling
pathways. Understanding the comparative
aspects of the structural elements of GnRHs
and their receptors can lead to the development
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INTERNATIONAL INNOVATION
Dr Stacia Sower outlines her
laboratory’s ongoing research
in identifying key reproductive
hypothalamic and pituitary hormones
in lamprey, which could provide the
scientific basis for better medical
therapies and an effective fisheries
management strategy
of novel interventive GnRH analogs
for better medical therapies
or for use in controlling
reproduction in fish
aquaculture. A
new method of
sterilisation
would also
be very
useful in
the field
of sea
lamprey
control
in the
Great
Lakes.
In what
ways have
your laboratory
and collaborators
been a major force in
demonstrating the value of the sea
lamprey as a model system for evolutionary
analyses? Indeed, can you expand on why
the sea lamprey is considered a viable and
useful model?
As an agnathan, the oldest extant lineage of
vertebrates, the sea lamprey has become a
model system for analysis of the evolution
of many genes and systems including the
evolution of the neuroendocrine regulation of
reproduction and the evolution of development
(EvoDev). Lampreys as basal vertebrates were
identified to be integral to evolutionary studies;
as
such,
the
mapping
of the lamprey
genome started
in Jan 2005 (www.
genome.gov/12511858). Nine
non-mammalian organisms were chosen
by the NIH for mapping the genome, each of
which represents a position on the evolutionary
timeline marked by important changes in
animal anatomy, physiology, development
or behaviour. It is estimated that the current
coverage of the genome is about 5.9X, which
infers that much of the genome has been
sequenced and available for analysis using
the trace archives and the partially assembled
genome by Ensembl.
Findings from your laboratory have
illustrated that the acquisition of the
hypothalamus was a seminal event in
vertebrate evolution. To what extent – and in
what sense – do these findings constitute a
major breakthrough in research?
Our existing data suggest the existence
of a primitive, overlapping yet functional
hypothalamic-pituitary-gonadal (HPG)
DR STACIA SOWER
Spawning new findings
Research focused upon lamprey – a fish species believed to have been
in existence for 500 million years – is delivering key insights into the
evolutionary development of endocrinal functions in vertebrates
and hypothalamic-pituitary-thyroid (HPT)
endocrine systems in this organism, involving
one or possibly two pituitary glycoprotein
hormones and two glycoprotein hormone
receptors as opposed to three glycoprotein
hormones interacting specifically with three
receptors in gnathostomes (vertebrates with
mouths and jaws). We hypothesise that the
glycoprotein hormone/glycoprotein hormone
receptor systems emerged as a link between
the neuro-hormonal and peripheral control
levels during the early stages of gnathostome
divergence. The significance of the results
obtained by analysis of the HPG/T axes in sea
lamprey may transcend the limited scope of
the corresponding physiological compartments
by providing important clues in respect to
the interplay between genome-wide events
(duplications), coding sequence (mutation),
and expression control level evolutionary
mechanisms in definition of the chemical
control pathways in vertebrates.
Can you shed light on your collaborations
with laboratories based at the universities of
Kitasato and Niigata, Japan? How have these
laboratories contributed to the project’s aims?
I, along with
Professor Hiroshi
Kawauchi
of Kitasato
University
in Japan,
have shared
students and researchers through a formal
collaboration that has produced more than 30
papers. Professor Kawauchi (now retired) and
two associates, Drs Takahashi and Moriyama,
have been collaborating since 1985. Some of
the many ongoing projects in my laboratory
are collaborative studies with my Japanese
colleagues. It all began because we were trying
to identify the lamprey Gonadotropin (GTH) in
1985-6. We thought it would take maybe two
years. In fact, it took us a little over 20 years and
we reported our results on the identification of
lamprey GTH beta. Most recently, we have now
published on the identity of hagfish GTH.
ONGOING STUDIES COORDINATED by Dr
Stacia Sower at the University of New Hampshire
have delivered groundbreaking findings relating to
neuroendocrine control in lamprey, an eel-like fish
species whose lineage dates back – astonishingly
– over 500 million years. The discoveries hold
substantial merit on two counts: firstly, in
phlyogenetic terms, the position of lampreys as a
basal vertebrate enables them to be a touchstone
for understanding the evolutionary development
of endocrinal systems in other vertebrates.
Secondly, from a long-term perspective, the greater
understanding of the underlying mechanisms which
dictate the reproductive processes in lampreys
will potentially be transferred and utilised in the
development of strategies to control reproduction
among certain fish species. Sower’s findings have
emerged from an area which is of high research
value to both marine conservationists as well as the
fisheries industry.
RESEARCH IN CONTEXT
Efforts to control the reproductive capabilities of
vertebrates are reliant upon a firm understanding
of the mechanisms which dictate neuroendocrine
activity and behaviour. In all vertebrates,
reproductive function is regulated by a region of
the brain called the hypothalamus, which – among
other roles – secretes a gonadotropin-releasing
hormone (GnRH). GnRH was first discovered in
1971 by Professors Roger Guillemin and Andrew
Schally, whose work was recognised when they
were awarded the Nobel Prize in Physiology or
Medicine in 1977. The discovery of GnRH has
proved monumental in the field of endocrinology;
it is now widely regarded as the ‘master molecule’
of reproduction, and has provided the focus for
decades of concerted and intensive research in
the field of neuroendocrinology. This, in turn, has
led to the development of current treatments for
infertility and cancers of the reproductive system
in humans. Such treatments have been arrived at
through the procurement of GnRH analogs, which
are modified peptides with the ability to work
more effectively than GnRH itself. As an indication
of their application, Leuprolide – one of the first
GnRH analogs to have been developed – is the
standard treatment for prostrate cancer, and is
also used to treat cases of precocious puberty and
female infertility. Indeed, the clinical application
of GnRH analogs as therapeutic drugs generates
over $5 billion per year in sales. Elsewhere, GnRH
analogs are used to stimulate ovulation in fish, and
have, consequently, become a useful and viable
tool in aquaculture.
GREATER DEMAND, DEPLETING STOCKS
In light of the increased market demand for fish
products, ascertaining a scientific basis on which
to develop strategies to control reproduction
among fish species is a growing priority for
commercial aquaculturists and other key players
within the fisheries industry. Where the farming of
commercially important species such as Atlantic
cod is concerned, eliminating the possibility of early
(pre-harvest) sexual maturation in individual fish
would result in an increase in the flesh quality of the
fish and an increase in somatic growth. A clutch of
methods are currently employed to delay puberty
in fish species. These techniques and approaches
include photoperiod control, induced triploidy,
monosex stocks, and selective breeding. However –
and in spite of the development of GnRH analogs
– major limitations still exist in the commercial use
of these methods, not least because the control
of reproduction is very complex and involves
LAMPREY NEUROENDOCRINE SYSTEM:
THREE GNRHS
AND THREE GNRH
RECEPTORS
Silver et al. 2005 Endocrinology 146:3351-61;
Aquilina-Beck, A, MacDonald, C, Kavanaugh,
S I, Freamat, M, and Sower, S A (2010). A
third lamprey novel GnRH receptor similar to
gnathostome type-II GnRH receptors, 92nd
Annual Meeting of the Endocrine Society, pp.
Abstr. P3-205, San Diego, CA.
FIGURE 1. Lampreys have three hypothalamic GnRHs that act via three GnRH receptors in some unknown differential manner.
WWW.RESEARCHMEDIA.EU 65
INTELLIGENCE
INSIGHT FROM LAMPREY GENOME:
STRUCTURE-FUNCTION STUDIES OF
NOVEL GNRH RECEPTORS
OBJECTIVES
The laboratory’s ongoing studies focus on
the molecular, biochemical and functional
studies to test the overall hypothesis
that lamprey GnRHs, GTH and their
receptor(s) share common functional and
developmental features compared to later
evolved vertebrates. The research embraces
new methodologies that are becoming
available through the disciplines of hormonal
genomics, proteomics and bioinformatics.
KEY COLLABORATORS
Professor Hiroshi Kawauchi, Kitsato
University, Japan
Professor Masumi Nozaki, Niigata
University, Japan
KEY FORMER GRADUATE STUDENTS
Dr Matthew Silver, Cell Signaling
Technology, MA
Dr Scott Kavanaugh, University of Colorado,
Boulder
Dr Mihael Freamat, Boston University, MA
FUNDING
NIH-NCRR
NSF
NH-AES
CONTACT
Stacia A Sower, PhD Professor
Director of Center for Molecular and
Comparative Endocrinology, Biochemistry
and Molecular Biology Program, Department
of Molecular, Cellular and Biomedical
Sciences
46 College Road
University of New Hampshire
Durham, NH 03824-3544, USA
T +1 603 862-2103
E [email protected]
www.unh.edu/biochemistry/sower/index.
html
STACIA A SOWER received her BS degree from
the University of Utah in 1973 and her MS and
PhD degrees from Oregon State University,
USA, in 1978 and 1981, respectively. She is
currently a Professor and Director of the Center
for Molecular and Comparative Endocrinology
at the University of New Hampshire, and is also
a member of the North American Society for
Comparative Endocrinology Council (2010-).
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INTERNATIONAL INNOVATION
several neuroendocrine and environmental factors.
Drawing on this, Sower comments: “In order to
control fish puberty or sterilise fish, we need to
understand the underlying mechanisms that trigger
and control puberty”. She continues: “The ongoing
research in my laboratory is to further identify key
reproductive hypothalamic and pituitary hormones
in lamprey and to determine interrelationships of
these hormones under specific reproductive stages
and environmental conditions”. Sower’s team of
dedicated researchers anticipate their programme
will provide key findings which will contribute to the
development of better medical therapies and novel
strategies for controlling reproduction in fish.
REARING ITS ANCIENT HEAD
In focusing upon lampreys – that is, the oldest
extant species on Earth – Sower’s research bears
enormous relevance in determining neuroendocrine
development in evolutionary terms. Indeed,
landmark findings that have recently emerged from
Sower’s laboratory illustrate that the acquisition of
the hypothalamus in lamprey was a paradigmatic
development in vertebrate evolution. She observes:
“The hypothalamic-pituitary (HP) system is
considered to be a vertebrate innovation and
seminal event that emerged prior to – or during – the
differentiation of the ancestral agnathans [jawless
fish]”. Despite the highly diverse life cycles and
reproductive strategies and behaviourial patterns
of vertebrate fish species, the endocrine system
observed by Sower and her team is, somewhat
incredibly, conserved throughout gnathostome
(species bearing mouths and jaws) lineages.
FINDINGS AND NEW HYPOTHESES
Sower’s team has adopted a multidisciplinary
approach to investigate the structure and function
of GnRHs in lamprey. By assimilating biochemical,
molecular, immunocytochemical and functional
studies, the team has determined that the lamprey
possesses a hypothalamic-pituitary-gonadal
axis and that there is a high conservation of the
mechanisms of GnRH action. However, while
Gnathostomes are generally seen to have two
GnRHs that act as hypothalamic hormones,
lampreys are the earliest evolved vertebrates for
which there are demonstrated functional roles
for three GnRHs that act via the hypothalamicpituitary-gonadal axis controlling reproductive
processes. Coupled with this, Sower’s group has
identified GnRH receptors in lamprey which
share several characteristics seen in type-I and
type-II vertebrate GnRH receptors. Highlighting
the significance of these findings, Sower states:
“The high conservation of GnRH and its receptor
throughout vertebrate species makes the lamprey
model highly appropriate for examining the GnRH
system in terms of its ligands and novel receptors”.
Furthermore, the team has recently located a novel
GnRH (called 1GnRH-II) and two novel GnRH
receptors (lGnRHR-2 and 3). This discovery has
provided a unique opportunity for comparative
and evolutionary analysis of the neuroendocrine
system in vertebrates.
Within this evolutionary context, Sower and her
collaborators have formulated a new hypothesis
relating to the neuroendocrine control of
reproduction in lamprey. The team proposes
that the neuroendocrine and thyroid functions
in the agnathan sea lamprey are simpler than
those exhibited in later vertebrates. This is
based upon the formulation that in lamprey,
one glycoprotein putatively interacts with two
receptors. “In our research, this transforming
paradigm serves as a model for analysis of the
evolutionary mechanisms leading to emergence
of the highly specialised Gnathostome endocrine
axes,” Sower affirms.
ROLE OF GENOMICS
As a marker of how much our understanding of the
neuroendocrine system in lamprey has advanced,
Sower recalls the paucity of knowledge that had
been gleaned when she first entered the field:
“When I started my studies 30 years ago, most
scientists did not think that the lamprey had the
same neuroendocrine system as all other jawed
vertebrates. This was an animal with a backbone that
we did not know anything about”. Today, however,
studies in this area are enhanced enormously by the
mapping of the lamprey genome. Indeed, the advent
of genomics has proven critical in the identification
of ligands, receptors, transcription factors and
signalling pathways. Although the lamprey genome
has not, as yet, been fully annotated, efforts are well
underway, with Professor Weiming Li of Michigan
State University leading a battery of international
scientists in this pivotal endeavour.