Zebra Fish New Discovered Sex Hormone (Secretoneurin) - fisheriesindia.com

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Thursday, 28 May 2020

Zebra Fish New Discovered Sex Hormone (Secretoneurin)

Zebra Fish New Discovered Sex Hormone (Secretoneurin) 

What is Sex Hormone?
Hormones, such as estrogen, testosterone or any of a class of steroid hormones that is produced especially by the ovaries, testes, or any part of the brain which affects the growth and functions of the reproductive organs or involved in the development of secondary sex characteristics in any animal or plant.

Secretogranin-2 occurrence

Kim Mitchell et al-2020 of university of Ottawa, capital of Canada altered secretogranin-2 is a protein encoded by secretogranin genes through specific mutation technique (using gene-editing technology) and found that it affected reproduction process in fish (female and male zebrafish unable to breed.

Importance of Secretogranin-2  
Secretogranin-2 is vital for the normal working of brain cells and other cells that secrete hormones to switch body functions such as growth and reproduction.

Key role of Secretoneurin
However, secretogranin-2 can get sliced up by distinctive enzymes that one small fragment called secretoneurin (33-amino acid neuropeptide) is a key player for stimulating sexual function in the Danio rerio (zebrafish) a model organism carp fish.

Secretogranin-2 in Human
In human, secretogranin-2 is produced by a gene named as SCG2 gene and is involved in wrapping or categorization of peptide hormones and neuropeptides into secretory vesicles.

Secretogranin-2 in zebrafish
Kim Mitchell et al., 2020 reported secretoneurin strictly reduced their sexual behavior in zebrafish. 

Effects of Secretogranin-2 on Sexual behavior
Mature fish look ordinary, but when both sexes are put together, they practically ignore each other as per researcher work published with titled “Targeted mutation of secretogranin-2 disrupts sexual behavior…….. PNAS, in press; doi: 10.1073/pnas.2002004117”.

Why Danio rerio (zebrafish) as a model organism?
  • Since zebrafish eggs are fertilized and developed outside fish body, it is an ideal model organism for studying early development.
  • Zebrafish has a genetic structure similar to that of humans. They share 70% of the genes with us.

 model organism zebrafish
Zebra-fish Model organism

Important Feature of Model organism
  • A model organism is a species that has been extensively studied, generally because it is easy to maintain and reproduce in the laboratory and has particular experimental benefits.
  • Model organisms are non-human species used in the laboratory to help scientists understand biological processes.

Ethical value for a model organism such as zebrafish
The body can prevent the transmission of disease from one species to another, thereby reducing fish mortality.
 As compared to invertebrates model organisms, they have more genes than other animals. As delicate organisms, special care must be taken when handling them.

Unique ability of Zebrafish
· Zebrafish has the unique ability to repair the heart muscle.

Zebrafish age value
  Breed zebrafish has an average life span of 3.5 years and can live up to 5.5 years.
 They show a gradual aging process.
 Spine curvature has been reported to be a common age-related phenotype.

Zebrafish is teleost
In recent decades, the tropical teleost zebrafish (Danio rerio) has proven to be an excellent backbone system for modeling mammalian molecular events that occur during embryonic development, organ formation, physiology and adults, under normal or pathological conditions.

Similarity between the genetic material of zebrafish and humans
 Zebrafish has a genetic structure similar to that of humans.
 84 percent of the genes known to be associated with human disease have a zebrafish equivalent.
 As a vertebrate, the zebrafish has the same main organs and tissues as humans.
 Our muscles, blood, kidneys and eyes share many characteristics with human systems.
Taxonomy of Danio rerio ((F. Hamilton, 1822)

Danio rerio

Advantages of zebrafish as a Model organism
Following are the advantages using zebrafish as a model organism for any time animal research work

External fertilization:
As zebrafish eggs are fertilised and grow outside the fish body. it can be used  for studying early embryonic development and hence  it is  ideal model organism to study developmental biology of animals including human

More progeny:
Zebrafish lays hundreds of eggs which ultimately leads more offspring available for the research work as compared to another model organism like rat

Small generation interval:
Generation interval or time for zebrafish is three or four months, that mean you will get mature within 3 to 4 months

Transparent eggs or embryos:
 Zebrafish eggs or embryos are nearly crystal clear or transparent which allows investigators to easily examine the development of internal structures easily by any type of microscopy

Genome information:
Whole genome of Zebrafish is available at different public database and it has a similar genomics structure to humans. Zebrafish share 70 % of genes with human.

Maintenance of fish:
Zebrafish is inexpensive to maintain than any other model organisms. You just need very small aquarium tank for maintaining it.

Vertebrate animal:
Zebrafish is a vertebrate animal, it has the same main organs and tissues as other vertebrate animals have e.g humans. Their muscle, blood, kidney and sensory organs system share many features with human systems

Morphological structures and growth rate:
Danio rerio have pigmented body, on the side of the body blue bands are present, which are reminiscent of a zebra's bands, and which range to the end of the caudal fin. Its growth rate is very fast and can grow up to 4–5 cm (1.6–2.0 in) in length.

During breeding time after introduce in breeding tank within a few minutes the male fish of zebrafish chases the female in a courtship procedural .After this, the female releases her eggs (spawning) to the water tank, and the male immediately fertilizes them as per natural phenomena. But In this work or experiment Kim Mitchell et al., 2020 found that only 1 out of 10 couples with mutated genes could spawn.

Fish carrying mutations produce eggs and sperm, but they do not breed with each other. When Kim Mitchell et al., 2020 injected secretoneurin into the body of genetically changed fish, fish can partially restore sexual functions.

Hence this technique can be used to increase spawning in commercial cultured fish species, or it can help human infertility treatments. Secretogranin-2 genes also produce many other hormone-like peptides with unidentified functions. In future, it will be exhilarating to explore this area of research work.

Note: Credit of writing this article( Zebra Fish New Discovered Sex Hormone (Secretoneurin) 
 goes to Mehar Zafer and Mohd Ashraf.

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