Embryonic development mapped, cell by cell

[lpetrich]

As cells divide in an embryo, they form a family tree, and one can find which parts are most closely related to which other parts. That's been done for nematodes and fruit flies, for instance, and it has now been done for zebrafish and frogs.

Tonight, 9pm Central…the conversation is here shows a video, There is no hat - YouTube, a video that shows at 25 minutes a picture of a family tree of zebrafish embryonic cells. I tracked it down, and I found a copy here:

McHeyzer-Williams on Twitter: "Developmental Trajectories with #SingleCell Resolution | #ZebraFish | AlexanderSchier @Harvard@Harvard @sciencemagazine [url]https://t.co/WE54quut2X… https://t.co/XdrzlYEMok"[/url]

I looked further, and I found Chronicling embryos, cell by cell, gene by gene | Science, A new view of embryo development and regeneration | Science, Single-cell mapping of gene expression landscapes and lineage in the zebrafish embryo | Science, Single-cell reconstruction of developmental trajectories during zebrafish embryogenesis | Science, The dynamics of gene expression in vertebrate embryogenesis at single-cell resolution | Science. There is a similar diagram in "Single -cell reconstruction of developmental trajectories during zebrafish embryogenesis" and I will refer to it.

Early cells:
- Germ cells, ancestors of the gametes: egg and sperm cells
- - Periderm or enveloping layer, an embryonic skin layer.
- - All the other somatic cells.

Somatic cells:
- Ectoderm
- Endomesoderm:
- - Axial mesoderm
- - Non-axial endomesoderm

Ectoderm:
- Epidermis
- Nervous system: major brain parts, sensory structures, the spinal cord, the neural crest

Axial mesoderm:
- Notochord (spinal-cord precursor)
- Prechordal plate (in the head)

Non-axial endomesoderm:
- Paraxial mesoderm
- Non-paraxial endomesoderm

Paraxial mesoderm:
- Trunk (along spinal cord):
- - Somites (muscle blocks)
- - Other muscle tissue
- Tailbud

Non-paraxial endomesoderm:
- Ventrolateral mesoderm: heart, kidneys, blood-producing tissues
- Endoderm
- - Pharynx (throat)
- - Pancreas, intestines


Note how the endoderm branches off from inside the mesoderm's branching. That seems to be typical of Deuterostomia: chordates, hemichordates, and echinoderms. But it's hard to find references to endomesoderm for protostomes like fruit flies and nematodes.

 

[Peez]

This stuff, together with genomics, is going to be Big.

Peez

 

[lpetrich]

Seems like the next targets for this research are chicken and mouse embryos. Chickens and mice have been used rather extensively as model systems for embryonic development because they are among the most humanlike of animals that are easy to work with in laboratories. Chimpanzees would be the best by evolutionary distance, but associated with that short distances are many of our deficiencies as lab animals: they are large, slow-growing, slow-reproducing, and highly social. They are also very deficient in an important feature of our species: language. The most success with chimps there has been in sign language, and they have been able to learn a sizable number of signs. But they are not able to string them together beyond two-sign combinations and a few three-sign ones.

Here is a family tree:

Bilateria
- Protostomia: Ecdysozoa
- - Arthropoda: Pancrustacea: Hexapoda: Endopterygota: Diptera: Brachycera: Drosophila melanogaster (fruit fly)
- - Nematoda: Caenorhabditis elegans (nematode)
- Deuterostomia:
- - Echinodermata: Echinoida: Strongylocentrotus purpuratus (purple sea urchin)
- - Chordata: Vertebrata: Gnathostomata: Osteichthyes
- - - Actinopterygii: Cyprinoformes: Danio rerio (zebrafish)
- - - Sarcopterygii: Tetrapoda
- - - - Batrachomorpha: Anura: Xenopus laevis (African clawed frog)
- - - - Amniota
- - - - - Sauropsida: Diapsida: Archosauria: Theropoda: Aves: Neognathae: Galloanserae: Galliformes: Gallus gallus (chicken)
- - - - - Synapsida: Therapsida: Mammalia: Placentalia
- - - - - - Laurasiatheria: Carnivora
- - - - - - - Caniformia: Canidae: Canis lupus (familiaris) (dog)
- - - - - - - Feliformia: Felidae: Felis silvestris (catus) (cat)
- - - - - - Euarchontoglires
- - - - - - - Glires
- - - - - - - - Rodentia
- - - - - - - - - Myomorpha
- - - - - - - - - - Muridae
- - - - - - - - - - - Mus musculus (mouse)
- - - - - - - - - - - Rattus norvegicus (rat)
- - - - - - - - - - Cricetidae: Mesocricetus auratus (golden hamster)
- - - - - - - - - Hystricomorpha: Cavia porcellus (guinea pig)
- - - - - - - - Lagomorpha: Leporidae: Oryctolagus cuniculus (rabbit)
- - - - - - - Primates: Simiiformes: Catarrhini
- - - - - - - - Cercopithecidae: Papionini: Macaca mulatta (rhesus monkey)
- - - - - - - - Hominoidea: Hominidae
- - - - - - - - - Pan spp. (chimp)
- - - - - - - - - Homo sapiens (human)


Many model systems have been chosen because they are easy to keep in labs, are fast-growing, and are fast-reproducing. This may cause biases in our understanding of embryonic development, because they may have adaptations for fast growth and fast reproduction.

A case in point: segment layout in fruit flies. They, like most other dipterans and some other insects, are "long-germ" insects, those that lay out their segments all at once. However, most other insects are "short-germ" insects, which grow most of their segments from their rear ends, or "medium-germ" ones, which are an intermediate state. This rearward growth is common among other arthropods, and it is also the typical way for annelids and vertebrates.

 

[lpetrich]

Cellular Development during Organogenesis - Comprehensive Interactive Cell List - LifeMap Discovery contains a diagram of embryonic development for biomedical research -- likely of human and mouse embryonic development

Its diagram:
- Ectoderm: epidermis, nervous system
- Primitive streak
- - Mesoderm
- - - Paraxial mesoderm: somites: bone, cartilage, skeletal muscle, dermis
- - - Intermediate mesoderm: urinary, reproductive systems (urogenital system)
- - - Lateral plate mesoderm: heart, blood, fat tissue, smooth muscle, limbs
- - Endoderm: gut tube: thyroid, lung, gastrointestinal tract, liver, pancreas

Rather closely paralleling zebrafish embryonic development, but with differences like migration of primitive-streak cells.


Endomesoderm & Ectoderm Models at EchinoBase | An Echinoderm genomic database -- has several sea urchins, a starfish, a brittle star, and a sea cucumber.

So ectoderm + (mesoderm + endoderm) is a shared deuterostome feature.