Lecture 4 - CSB325

Origin of Life: Synthesis of Prebiotic Chemicals

Extraterrestrial Origins: Meteorites with organic material PAH, amino and organic acids, ketones Alcohols, purines, C10

Terrestrial Origins: Amino acids, sugars, purines from CH4, NH3, H2O, N2

CSB$325$Lecture$4:$Hormone$Evolu7on$

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hormones were part of the earth(?)

Figure 2-2: History of the evolution of the Earth and approximate times of the major

stages in the evolution of life.


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Physiological Requirements: Internal Conditions -energy -raw materials

Environmental Conditions: External conditions

-Acceptable conditions-growth/metabolism -Poor conditions-quiescence

When cells can coordinate these signals, they begin to live within a community either singly or communal and begin to establish a division of labour and therefore specialization of function


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might have created multicell orgs through endocrine sys

Theories of Prebiotic Synthesis: Energy Sources

There were, in theory, several sources of energy that could have been used for the prebiotic synthesis of organic chemicals

Sunlight

Lightning

Geothermal vents

Cosmic Radiation

Volcanic activity


Figure 2-1: Examples of organic compounds present in the prebiotic Earth. Such

compounds were used as substrates and building blocks for more complex molecules.


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NH4

A

B

C

D

E

Evolution of Protocells

Association of organic material on inorganic substrate

Concentration of organic material

Partitioning of Hydrophilic and Hydrophobic material

Formation of Hydrophobic membrane

Separation of protocell From substrate


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there was an E gradient


Protocells and First Signalling Networks

What is a protocell?

Partitioning of biotic and non-biotic environments The need to signal

Theoretical evolution and structure of a protocell

Partitioning of hydrophilic and hydrophobic molecules Development of lipid membrane Ion gradients across membrane and energy production Signalling capacity Membrane diffusion Pores in membrane Protein channels Early adhesion proteins


Protocells, as we examined had only a random and intermittent signaling capacity with little, if any, coordination between the excreted Molecule and the regulation of activity of another protocell. Once viable living cells developed, coordination between the secreted Molecule and the activity of the target cell was essential.

The expression of receptors on the target cell determines the specificity of hormone action


First Cells and Signaling Ability First true cell

Metabolic and genetic replication ability Required Attributes

Stable membrane Cytoskeleton adhesion signaling system endocytosis, exocytosis Reasonably accurate replication

Evolution

2 billion years from first cell to first multicellular animal Elaboration of membranes act as a substrate for biosynthetic enzymes required for exocytosis and endocytosis Symbiosis with other organisms Transformation from anaerobic to aerobic formation of organelles


Figure 2-11: Increase in cellular complexity by symbiosis. The formation of organelles

occurs by the ingestion or infection of other cells. Overtime, a symbiotic relationship is

formed. Intracellular or intracrine signalling pathways are required to coordinate the

actions of the new organelle with the actions of the rest of the cell.

Symbiotic cells – increase of complexity


Selection of Types of Signaling Molecules

Amino acids among first amino acids synthesized acid/base ability form elongated chains Peptides and Proteins structural and signalling ability several types of structural organization can carry and transmit information Lipids pass through membrane early prebiotic synthesis Gases and ions present in prebiotic Earth Nucleic acids common as signal molecules but evolutionary origins are not clear Sugars not common as signalling molecule ! !!


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impart a lot of E and are hydrophillic might not be greatsog mols because they dissolve

Figure 2-15: Evolution of signalling systems in the Metazoa.

A possible timeline for the evolution of cells and their signalling systems


Problems associated with the development Of multicellularity: 1. Adhesion;cells need to be physically connected or attached 2. Nutrient, ion, water, oxygen transport to inner cells 3. Coordination of function: signalling systems 4. Procurement of nutrient sources


Signaling Processes Earliest Cells:

Intracrine and Exocrine abilities More evolved systems

Autocrine/Paracrine mechanisms Juxtacrine Mechanisms

Membrane Mechanisms

Simple and facilitated diffusion Channel and transporter mediated diffusion


Basic signaling systems: Growth and Differentiation

feeding, growth maturation cell cycle differentiation cell death

Sensory systems

locomotion toward food source away from danger chemical (olfactory input) visual (input) geotaxis mechanical


Figure 3-8: Phylogeny of the phylogenetically oldest lineages of metazoans.


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know how the signalling systems evolved

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know the taxonomy

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distinct organismsevolved from single celled orgs

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basal orgs = something that's close to the original

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no symetry between sponges and placozoans

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us

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mollusks and insects

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second mouth = opening

Simplest$Known$Metazoan$

Trichoplax adherens Phylum Placozoa No endocrine or nervous system asymmetrical


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the only signalling they have might beparacrine signalling. ionic transmission like gap junctions. simple signalling systemdoesn't require much sophistication to communicate and stuff

Signaling in primitive Extant Metazoans

Placozoa and Poriferans as models of early metazoans role of extracellular matrix

Trichoplax adherens as a model

asymmetrical, two tissue types autocrine paracrine signalling only


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Figure 3-10 Photoreception in a sponge larvae. Cilia, associated with a ring of

photoreceptive cells at the base of the larve act to propel the organism away from

sunlight. Reprinted with permission from Leys and Degnan (2001) Biol. Bull.

Epithelial cells of the Poriferans (Sponges) are capable of transmitting

signals

No true nervous system with axons and action potentials


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works the same way as placozoans. so don't know if they're sister types or how they're related. they're negatively phototaxic, take the larva are symetrical, their photoreceptors can stimulate the surrounding cells by gap junctions which can stimulate the flagella moving it away from light. it's capable of behavior despite the lack of NS

Formation of the Nerve net with Neurons and neurosecretory cells

Placozoans and poriferans do not have nervous systems, however the Radiate phyla, Ctenophora and Cnidaria do. There are no known metazoans that display transitional forms of the nervous System. Phylogenetically older species of deuterostomes and protostomes also show The presence of a nerve net, We assume that the first functional neural/neurosecretory system was a nerve net.


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have a reasonably elaborate NS, there's no transitional forms doe, don't know how it got to that point. but they go have a nerve net, which is fundamentaly different from how we do it. looks like the next slide

A model of a nerve net


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blue = somatic cells, the other cells are neurosecretory cells, which are connected by axons and are in communication with each other, they get stimulate and interact with each other. can efficiently regulate the somatic cells

Figure 3-13 Nerve net in Hydra. A network of nerve cells is seen in A) hypostome B)

peduncle and C) basal disc after visualization with an anti vasopressin antiserum. See text

for additional details. The scale bars represent 100 µm. Reprinted with permission from

Morashita et al (2003) Elsevier Ltd.

Immunohistochemical visualization of a Nerve net in Hydra


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Signaling Systems in the Radiata Growth and Differentiation pathways comparatively well developed Wnt/frizzled pathway:

wnt (wingless) ligands: a family of polypeptide ligands frizzled receptor: a family of proteins consisting of membrane bound receptors with 7 alpha helices Similar to G-protein coupled receptors but without the G-protein component.

Nuclear receptors: similar to steroid-thyroid hormone receptors although

ligands are not well understood Serine/threonine and Tyrosine kinase based systems Sensory type pathways present

G-protein coupled receptors are present but in low numbers and diversity


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frizzled = GPCR and is a very early version of it.

Formation of the Nerve net with Neurons and neurosecretory cells

The first neuron/neurosecretory cells may have been derived from Early sensory cells These cells released a chemical signal via a robust depolarizing current resulting from the appropriate sensory input. Later these cells evolved into a new morphology with extended Process that could interact with structures associated with movement And feeding (ie. Cells with cilia). As movement became more complex, interneurons evolved and bridged The sensory cells with the locomotory cells


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Evolution of Signaling pathways

Sensory cell

Locomotor cell with cilia

Sensory input

Ionic coupling

Nervous


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pre nervous type of system.

Sensory cell


Sensory input

Ionic coupling

Nervous

Sensory cell

Sensory input

Chemical secretion and paracrine diffusion

Neuroendocrine



Sensory cell


Sensory input

Ionic coupling

Nervous

Sensory cell

Sensory input


Neuroendocrine

Sensory cell

Sensory input


Endocrine

Non-nervous (depolarizing) Secretory cell



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primitive NS

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primitive

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primitive

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these two splitand specialized

Genetic and Morphological Complexity and Signalling Systems: Key points

Development of Nervous and Vascular Systems

Integration of sensory systems and locomotor systems Formation of nervous system and integration with vascular system

Triploblastic organism

Formation of all known bilateral metazoans Increase in complexity of signalling systems


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endocrine and NS developed complementary systems b/c NS = fast but can only reach few cells and endo = slow but reaches all cells .

Relationship among symmetry, endocrine system, and the nervous system

How an organism moves has a bearing On where sensory organs are located. Once bilateral symmetry evolved, then Sense organs could be concentrated In the direction of movement (i.e. head)


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not the most efficent way of moving

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more efficient, looks like a pnacake and move in two dimensions, sensory sys can be located on the edge, the NS linked all fo these things they have radial NS.

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most efficient. they move along one direction. the sensory organs become concentrated on one secion. the amount of E to create a small but efficent it less than the first one. the amount of E utlized for movement is also lesscompared to the other ones.


Relationship among symmetry, endocrine system, and the nervous system

Symmetry allowed for structural similarity among individuals of a population A systemic signaling system could therefore develop in same way in all

individuals. This set the foundation for co-ordination among sensory systems, feeding,

and locomotory structures. This could not be consistently achieved in a non symmetrical animal.


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more effective. it also creates a behaviour which allows them to interact with each other even more and they come together as a population

Basal (phylogenetically older) Lineages of bilateral animals

Deuterostomes Protostomes Acoela

Echinoderms Ecdysozoa Lophotrochozoa

Molluscs Arthropods Chordates

Radiata

Placozoa Porifera

Precambrian explosion

Triploblastic animals

Moving forward toward the Chordates


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pangenomic theory that somehow the genomesweere similar (?) find more info

Figure$4B2$Evolu'on!of!the!nervous!system!

Formation of the Chordate Nervous System Plan

Segmentation Encephalization Dorsal nerve chord

Radiates: Nerve ring Nerve net

Ventral nerve chord

Segmented nervous System with Ganglia and Ventral nerve chord


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bilateral animals. we see the beginning of a NS

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protestomes

A few words about Endocrine systems…

Any cell that evolved the capability for robust paracrine secretion had the potential to become and endocrine cell. These cells were present in all the basic tissue types of the earliest Metazoans, therefore, all tissues had the capability of becoming Endocrine organs. In fact, this is the case today: all tissues and organs have a variety of Substances that are secreted into the blood stream. Therefore, all organs, by definition, may be considered endocrine organs.


Nervous-Endocrine Interactions

Nervous component

Neuroendocrine component

Releasing Factors Neurohormones Endocrine

component

Sensory Information

Tissues

Neurotransmitters Neuromodulators

Neurotransmitters Neuromodulators

Hormones


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are small mobile molecules

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mostly peptides

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they cover everything

General Organization of the Vertebrate Brain

Nerve cord/spinal cord

Hindbrain rhombencephalon

Midbrain mesencephalon

Forebrain prosencephalon

The brain is bilateral consisting of both left and right halves. One side is basically a mirror image of the other. This means also that the neuroendocrine cells are similarly divided.


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shark brain

Human brain development


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midbrain

Figure 4-13 Organization of the vertebrate nervous system A) Central Nervous

System B) Spinal Cord and ganglia


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most is on diencephalon main component

Ventricles of the Brain

I

II III IV

The brain and nerve cord are hollow and consists of four ventricles filled with cerebral spinal fluid

Forebrain Midbrain Hindbrain


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fishes, sharks, amphibians


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evolution, folded back on its self

Cerebrospinal fluid CSF

Resembles ultrafiltrate of plasma There are no substances in CSF that are not found in plasma Proportions differ

I

II III IV

No diffusion barrier

Brain-blood barier There is a barrier between CSF and blood.


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protects brain from shockand stabilizing itand also clears out shit form there

Figure 4-15 Basic components of the vertebrate blood brain barrier

Blood-brain barrier


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can expand and contract to allow openings


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windows or holes

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ones that are fat soluble they passthrough BBB very easily which thewater soluable can't

Blood-brain barrier

Passive diffusion: water, lipophilic (steroids, ecosanoids) drugs (barbiturates) alcohol

Transported: glucose, neutral amino acids used for neurotransmiter synthesis Peptides such as met-enkephalin, IL1, NPY, MCH, CRF use saturatable Transporters Peptides such as calcitonin, amylin, adrenomedulin enter via specific receptors In circumventricular organs


Figure 4-16. Position of circumventricular organs in a human brain

CSB$325$Lecture$4:$Hormone$Evolu7on$Pineal gland – melatonin, rhythms Subfornical organ – regulates fluids, osmoreceptor cells Organum vasculosum – peptides, osmoregulation, fever Area postrema – vomiting centre, osmoregulation Median eminence associated with anterior pituitary Neurohypophysis: neurosecretion AVP, oxytocin

III ventricle

Anterior lobe Anterior Hypophysis (Pars distalis)

Posterior lobe Posterior Hypophysis (Pars nervosa)

Intermediate lobe (Pars intermedia)

Optic chiasm Median

eminence

Hypothalamus

The pituitary gland consists of two main lobes: Anterior Lobe:epithelial tissue Posterior Lobe: nervous tissue

General!Structure!of!Pituitary!Gland!


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rostral front

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caudal

Mammalian Brain Development

Neural plate Ectoderm Neural tube

Neural crest


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not on the exam

Ontogeny of the Pituitary Gland in Amphibians


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not on the exam

Structure of Human Hypothalamic-Pituitary Portal System


Hormones Produced in the Pituitary Gland

Anterior Pituitary Gland Cell Type: Gonadotropes: Follicle Stimulating Hormone (FSH) Luteinizing hormone (LH) Thyrotropes: Thyroxine stimulating hormone (TSH) Corticotropes: Adenocorticotropic Hormone (ACTH) Somatotropes: Growth hormone (GH) Lactotropes: Prolactin Somatolactotropes: Somatolactin (fishes)

Posterior Pituitary Gland

The posterior lobe consists of neurosecretory terminal originating from cells in the hypothalamus. In mammals, there are two main hormones that are released: Vasopressin and Oxytocin. In non-mammals variants of vasotocin are released.


Chordate Evolution and Phylogeny


Figure 4-18. Neural Complex in a Tunicate. A number of hypothalamic and pituitary

hormones and processing enzymes have been found in the neural complex suggesting a

relationship with the chordate hypothalamo-pituitary system. See text for further

details.CS, cloacal siphon; OS, oral siphon. Reprinted with permission from Kawamura

et al, (2002) Elsevier Science (USA).

Neuroendocrine secretion in a Tunicate


Structure of Agnathan Pituitary Glands The jawless fishes, or agnathans, are the most primitive known chordates. These fish which include the hagfishes (Myxini) and the lampreys (Cephalospidomorphi) are separate classes. The hagfishes lack a vertebrae and therefore are not classified As vertebrates. The Cephalospidomorphi do possess a vertebrae and are considered The phylogenetically oldest vertebrates. The Cephalospidomorphi likely evolved At least 50 million years after the Myxini. Both groups of fishes are highly degenerate. Despite this, there are common aspects to their structure of pituitary and hypothalamus That provide us with clues as to how this system evolved in the vertebrates

Hagfish Class: Myxini

Lamprey Class: Cephalospidomorphi

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Myxini Cephalospidomorphi

Agnathan Pituitary Structure

For both the Myxini and the Cephalospidomorphi there appears to be a complete separation of the pars distalis from the rest of the hypothalamus. Diffusion of the hypothalamic releasing factors appears to be the main route of communication between the hypothalamus and pars distalis. However, a simple portal system may be present although this is unclear. In hagfishes, (Myxini), the pars nervosa is a relatively undifferentiated part of the hypothalamus where the axonal termini of neurosecretory cells impinge on a vascularized region at the hypothalamus wall. In lampreys (Cephalospidomorphi) the pars nervosa becomes more differentiated into a discrete lobular structure.

Pars distalis Pars intermedia Pars nervosa

Structure of Agnathan Pituitary Glands CSB$325$Lecture$4:$Hormone$Evolu7on$

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communicate throughstemic bloodsnot efficentbut it works

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much closer association with distalisn and nervosa

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both don't have cortical sys

Hagfish and lampreys may also utilize the systemic blood as a route for releasing factors to regulate the pars distalis Ectopic transplantation of the hagfish pars distalis in other regions of the body, for example do not appear to compromise the normal physiology of the these animals. The various cell types in the pars distalis are relatively intermingled.

Structure of Agnathan Pituitary Glands


The Class Chondrichthyes or cartilaginous fish are the phylogenetically oldest Group of gnathostomes or jawed fish. The cartilaginous fish include the Subclass Elasmobranchii (sharks, skates and rays) and the Subclass Holocephali (chimaeras). The cartilaginous fish evolved 50-100 million years After the lineage leading to the lampreys and about 400 million years before Present. The Elasmobranchs and Holocephali diverged early in Chondrichthyan evolution, but still possess a number of related features.

Elasmobranchii Holocephali

Chondricthyan Pituitary Gland

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General Structure of Elasmobranch Pituitary Gland

Pars nervosa

Pars distalis

Pars intermedia

Portal system The Elasmobranch pituitary consists of a fused pars nervosa and pars intermedia. In this situation where there is considerable Intermingling of pars nervosa and pars Intermedia, it is referred to as a pars Neurointermedia or Neurointermediate lobe. There is a well developed portal system that connects most of the pars distalis with the hypothalamus. However, the ventral lobe, has no vascular or nervous connection to the rest of the brain. Releasing factors are secreted into the systemic blood supply to communicate with the ventral lobe.

Neurointermediate lobe


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Elasmobranch Pituitary Organization

Ventral lobe

Pars Distalis Pars Nervosa

Portal System

The elasmobranch pars distalis consists of a second lobe ventral to the main Body. This structure is called the ventral lobe and is connected to the rest of The pituitary by a thin stalk of tissue. The ventral lobe does not appear to have Either a vascular or nervous connection to the rest of the brain.

A view of the elasmobranch pituitary gland


Pituitary and Diencephalon Structure in the Holocephali

Buccal lobe

Brain

Position of Pituitary Gland

The structure of the pituitary in holocephalans is similar to that of the Elasmobranchii. The main difference lies in the structure of the ventral lobe. In holocephalans, the ventral lobe is called a buccal lobe and is found in the roof of the mouth. It is separated from the brain by a layer of cartilage. The hypothalamus communicates with the buccal lobe by secreting releasing factors into the systemic blood.


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Although there are few studies to draw upon, the location of cells in the pituitary gland in the Cartilaginous fish appears to have some organization. For example, the gonadotropes are located primarily in the ventral lobe of elasmobranches (or the buccal lobe of holocephalons). Although there is some interdigitation of the pars nervosa with aspects of the pars distalis, there is currently no evidence that there is any direct neural link between the hypothalamus and pars distalis.However, given the organization of the neurosecretory cells of the hypothalamus and the presence of interdigitation in cartilaginous fish, there is the distinct potential that some form of rudimentary neural connection may exist. If so, one might also expect that some of the basic pituitary cell types are organized to a limited degree in clusters of related cells.

Pituitary Cell Organization in the Cartilaginous Fish


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interdigitation

The Actinopterygian-Sarcopterygian Bifurcation And Pituitary Evolution

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Ray-finned fish lineage (Actinopterygii)

Lobe-finned fish lineage (Sarcopterygii)

Around 350 million years ago, vertebrate evolution followed two main pathways. One group of fishes exploited a niche associated with the ocean and lake bottoms whereas another group exploited a pelagic niche. The bottom dwelling group adapted robust and limb-like fins and developed into the lobe-finned fishes (Sarcopterygii) and ultimately to land animals. The pelagic adapted lineage developed into the ray-finned Fishes (Actinopterygii). Pituitary evolution followed separate morphological patterns in each group.


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at the bottom

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teleosts

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amphibians reptiles us

Evolu7on$of$the$Pituitary$Portal$System$

Early jawed vertebrate

Lobe-finned fishes/tetrapods Ray-finned fishes

oc

oc

oc

vIII vIII

vIII

Elaboration of portal system Direct neural connection

Jawed vertebrates began with a pituitary structure similar to chondrichtyan fishes where there was a portal system and a more or less distinct pars distalis and pars nervosa. In the lobe-finned fishes and tetrapods, the portal system became more developed, whereas in the ray-finned fishes the portal system was lost and a direct neural connection developed

Neurosecretory cells With projections to The median eminence And portal system

Neurosecretory cells With projections to the pars nervosa


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cells are intermingled here

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cells are clumped by groups

Amniotes The earliest amniote tetrapods appears about 30 million years after the evolution of the first amphibians. This group includes the mammals, reptiles and birds, and refers to the amniotic egg present in all groups. The early amniotes began to radiate extensively in the Carboniferous and early Permian times, displacing the non-amniotes (early amphibians) from those habitats and niches. Evidence suggested that virtually all of the early amniotes were carnivorous. The extensive radiation of insects at this time is thought to have been a food source that was exploited by the early amniotes thus acting to stimulate this radiation of species. Physiological changes that accompanied this adaptation included changes in respiratory mechanisms, diuresis and excretion, reproduction and integration of sensory systems.

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Phylogenetic Position of Amniotes


Structure of Reptile Pituitary Glands

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rhynchocephalia

chelonia

crocodilia

squamata squamata

There are four subclasses of reptiles: Chelonia (tortoises, turtles and terrapins), Rhynchocephalia (tuataras), crocodilia (alligators, crocodiles, caimans, gharials) And squamata (lizards snakes).


Structure of Reptile Pituitary Glands

The general arrangement of the reptilian pituitary is more or less similar in most of the groups. Differences are most apparent within the pars nervosa morphology. The phylogenetically older reptile groups such as the chelonia (turtles) and rhynchocephalians (tuataras) tend to have a pars nervosa with some interdigitation of the pars intermedia. Note also in all reptiles is an expanded portal system and generally a mix of pituitary cell types instead of clusters of similar cells.

Rhynchocephalia Chelonia

Crocodilia Squamata (lacertilia)

(lizards)

Squamata (ophidia) (snakes)


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similar to mammals

Structure of Teleost Pituitary Gland

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The Teleostei are a vast assemblage of fish that include about 25,000 species. The pituitary gland is unusual in that cells of the pars distalis are clustered in nuclei of similar cells. There is extensive interdigitation of the neural lobe with the rest of the pituitary, and direct neural connection between the hypothalamus And pars distalis


Anguilla anguilla (eel) as a model for the teleost pituitary gland

The teleost pituitary gland morphology represents the most advanced structural features among the fishes. Two major changes have occurred: neurosecretory cells of the hypothalamus send their axons through the extensive interdigitations of the pars nervosa with the pars intermedia and pars distalis. Within the pars distalis cells have become grouped into discrete clusters. Thus, in this manner the releasing factor can stimulate the appropriate pituitary cell.

Neurosecretory cells of the hypothalamus

rostral

OC



Any$Ques7ons???$

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Lecture 4 - CSB325

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