Research Article
Open Access
Germ Cell Transplantation in Teleost Fishes: A
Viable Approach for Germline Conservation
Sullip Kumar Majhi*
ICAR-National Bureau of Fish Genetic Resources, Canal Ring Road, Dilkhusa P.O., Lucknow 226 002, Uttar Pradesh, India
*Corresponding author: Dr. Sullip Kumar Majhi, ICAR-National Bureau of Fish Genetic Resources, Canal Ring Road, Dilkhusa Post Office, Lucknow 226002, Uttar Pradesh, India. Tel: + 91-522-2442441; Fax: + 91-522-2442403; Email:
ingapoletaeva@mail.ru
Received: March 28, 2018; Accepted: September 11, 2018; Published: September 20, 2018
Citation: Sullip Kumar M (2018) Germ Cell Transplantation in Teleost Fishes: A Viable Approach for Germline Conservation. Int J Gen Sci 5(2): 1-6. DOI: 10.15226/2377-4274/5/1/00124
Abstract
Germ cell Transplantation, a powerful assisted reproductive
technology, is widely used for basic and applied research. This
technique, initially developed for mammals, has been recently used
for teleost fishes for conservation and propagation of elite germplasm.
In this technique, germ cells derived from donor fish are transplanted
into the gonads of sterile recipients through surgical and non-surgical
interventions (through genital papilla). The recipients upon attending
sexual maturity are crossed through artificial insemination and
natural spawning to generate surrogate offspring. The vast fishery
resources could be effectively managed by germ cell Transplantation
technique, especially to rejuvenate the population of endangered
fish species or commercially important species which are too large
for hatchery rearing and, that do not spawn due to the stress of
confinement, or whose maturation cycle is associated with complex
migratory behavior which cannot be reproduced in captivity.
Keywords: Fish; Conservation; Surrogacy; Germ cell Transplantation; Endangered;
Keywords: Fish; Conservation; Surrogacy; Germ cell Transplantation; Endangered;
Introduction
The great diversity of aquatic ecosystem, from marine to
freshwater, harbors almost 30,700 fish species. However, rapidly
changing climate and associated factors such as pollution, habitat
loss and increasing anthropogenic pressure on the water bodies
have played a crucial role in turning a number of fish species to
become extinct or endangered (see http://www.iucnredlist.org).
There are two major approaches to conserve these threatened fish species such as ex situ and in situ approach. The in situ approach involve the preservation of habitat on a large scale, thereby protecting the species within the ecosystem [1,2]. Contrary, the ex situ approach involve conservation of these valuable germlines and propagate the individual species through breeding in captivity [3,4]. Although, there has been debate about the relative efficacies of these strategies, both obviously have merit. Ideally, habitat preservation should always be the highest priority, that help to protect entire ecosystems and many species simultaneously while concurrently retaining the inherent ‘wildness’ of nature, animals and aquatic plants [5]. However, the ability to conserve habitat long term is itself under constant threat from natural stochastic factors, local changes in land use and natural resource management choices. For sustainable management of genetic resources, it is my understanding that, both in situ and ex situ approaches should be complementary rather than competitive.
There are two major approaches to conserve these threatened fish species such as ex situ and in situ approach. The in situ approach involve the preservation of habitat on a large scale, thereby protecting the species within the ecosystem [1,2]. Contrary, the ex situ approach involve conservation of these valuable germlines and propagate the individual species through breeding in captivity [3,4]. Although, there has been debate about the relative efficacies of these strategies, both obviously have merit. Ideally, habitat preservation should always be the highest priority, that help to protect entire ecosystems and many species simultaneously while concurrently retaining the inherent ‘wildness’ of nature, animals and aquatic plants [5]. However, the ability to conserve habitat long term is itself under constant threat from natural stochastic factors, local changes in land use and natural resource management choices. For sustainable management of genetic resources, it is my understanding that, both in situ and ex situ approaches should be complementary rather than competitive.
Germ Cell Transplantation
Germ Cell Transplantation (GCT) appears to be a viable
and promising approach for ex situ conservation, a technique
originally devised for use in mammals. The GCT was first
demonstrated in mice and was performed with dispersed
testicular Cell suspensions containing unknown numbers of
spermatogonia derived from donor males and microinjected
into sterilized male recipients, leading to establishment of
donor-derived spermatogenesis [6]. Since then, the technique
has been extensively used for the purpose of basic research [7],
reproductive medicine [8] and treatment of infertility [9], but
surprisingly remains, in part, unexplored in fish, even though
GCT has potential applications in conservation and propagation
of species facing eminent extinction (Figure 1-3).
Figure 1: Potential applications of GCT in production of surrogate offspring. Using this technique, commercially important species and/or difficult to bred fish species can be quickly propagated by transplanting GCs from target species into closely related recipient, preferably the one that can be easily bred in captivity. A) The recipient fish. B) The endogenous germ cell of recipient fish is depleted by heat-chemical treatments. C) Germ cells are harvested from the donor fish. D) The cells are labeled with fluorescent dye and transplanted into recipient gonad through genital opening. E) Months after the procedure, transplanted cells differentiated into functional gametes; F) Surrogate parents are artificially inseminated or allowed natural spawning. G) Production of donor-origin progeny.
Figure 2: Schematic presentation of germ cell transplantation technique in transgenic fish production. A) Selection of a donor fish. B) Germ cells are harvested from the gonads of donor fish. C) The germ cells are transfected in vitro. D) The transfected cells are transplanted into allogeneic recipients those are prior depleted of endogenous germ cells. E) After attaining sexual maturity, the surrogate animal are crossed with its pure counterpart. F) Mass-scale production of transgenic progeny.
Figure 3: Schematic presentation of revitalizing the fishery of endangered species. The GCs from endangered species transplanted into xenogeneic sexually competent adult recipients can make it possible to regenerate them, even in case of last one survivor. A) Selection of an endangered fish. B) Germ cells are harvested from the endangered fish species. C) The gonadal cells are cyopreserved in liquid nitrogen for posterity use. D, E) The stored cells are recovered by thawing and labeled with fluorescent dye and transplanted into recipients. F) After attaining sexual maturity, the surrogate parents are induced breed or allow natural spawning. G) Generation of donor-derived progeny, thereby reviving the fishery of endangered species.
However, early beginning of this century has given us a
much awaited breakthrough, a similar approach that was
originally proposed in mammalian model, was developed in
fish using Transplantation of Primordial Germ Cells (PGC)
carrying GFP (Green Fluorescent Protein) into peritoneal
cavity of rainbow trout hatchlings resulted in production of
sperm with donor genetic characteristics [10]. Further, using
the same methodology, xenogeneic Transplantation between
rainbow (Onchorhynchus mykiss) and masu (O.masu) trout
were also successfully performed [11]. Also, it was shown
that PGCs can be cryopreserved for prolonged periods of time
before Transplantation and still establish spermatogenesis in
the recipient testis [12]. However, GCT using embryos and/or
hatchlings requires very sophisticated instruments for the GCs
isolation and quantum of labor for their Transplantation to the
target site. Above all, the transplanted embryos and/hatchlings
take considerably long time to reach adulthood and to produce
the donor-derived functional gametes, adding considerably to the
cost of producing surrogate gametes. Consequently, the hatchery
units, which are the end user of the technique might reluctant
to adopt the technique for the commercial production of valued
fish seeds. In contrast, development of surrogate broodstock
development involving Transplantation of spermatogonia
Cells derived from target species into a closely related adult
fish species, depleted of endogenous germ Cells using suitable
ablative strategy and, for which captive breeding technique are
well developed, has considerably shorten in production of donorderived
gametes and, make the technique of GCT more simple and
viable to be practically feasible for the end users [13-15]. In our
previous studies, we examined the feasibility of xenogeneic GCT
in adult fish using two congeneric model species of atherinopsid
fishes, the pejerrey (Odontesthes bonariensis) and the Patagonian
pejerrey (O. hatcheri) as donor and recipient, respectively [13,15].
We had chosen these two species as experimental model due to
the wealth of basic information available on their reproductive
physiology, can be easily bred in captivity and availability of
several genetic markers to distinguish them [16,17].
In those studies we had reported that the heat-chemical treatment successfully induces germ Cell depletion in Patagonian pejerrey [18], obtention of surrogate sperm following surgical implantation of donor pejerrey germ Cells into recipient Patagonian pejerrey testes [13] and, Transplantation of donor pejerrey germ Cells into recipient Patagonian pejerrey gonads through genital papilla produce surrogate eggs and sperm [15]. The results of those studies have collectively explore in-depth in understanding efficient preparation of sexually competent recipients, process of donor Cells colonization inside the recipients’ gonads and functional properties of donor-derived gametogenesis in terms of germline transmission. To my knowledge, those were the first reports on GCT using adult fish as recipients that generated viable offspring by both artificial fertilization and natural spawning, which demonstrates the viability of the technique.
In those studies we had reported that the heat-chemical treatment successfully induces germ Cell depletion in Patagonian pejerrey [18], obtention of surrogate sperm following surgical implantation of donor pejerrey germ Cells into recipient Patagonian pejerrey testes [13] and, Transplantation of donor pejerrey germ Cells into recipient Patagonian pejerrey gonads through genital papilla produce surrogate eggs and sperm [15]. The results of those studies have collectively explore in-depth in understanding efficient preparation of sexually competent recipients, process of donor Cells colonization inside the recipients’ gonads and functional properties of donor-derived gametogenesis in terms of germline transmission. To my knowledge, those were the first reports on GCT using adult fish as recipients that generated viable offspring by both artificial fertilization and natural spawning, which demonstrates the viability of the technique.
Conclusion
The investigations we reported earlier are believed to have
broader implications in the vast fishery resources management.
For example, the treatment protocol we developed for recipient
preparation might also be handy for preparation of sterilized
population with minor modification, which, beside useful for
GCT can also be applied in aquaculture for sex control and/or
control of nuisance fish species (yet a hypothesis). Further, the
protocol we developed for GCT might also help in conservation
of endangered and/or extinct fisheries resources and revive the
fishery of such species in a considerably short period. Also, the
technique can be useful in speedy propagation commercially
important species which are too large for hatchery rearing and,
that do not spawn due to the stress of confinement, or whose
maturation cycle is associated with complex migratory behavior
which cannot be reproduced in captivity.
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