Lecture 19- Post-embryonic development: metamorphosis, regeneration, and aging

Modes of insect development include; __________________ (gradual) metamorphosis in a cockroach. Describe

Hemimetabolous, After a very brief pronymph phase, the insect becomes a nymph. After each molt, the next nymphal instar looks more like an adult, gradually growing wings and genital organs

Modes of insect development include; ____________________ (complete) metamorphosis like in a moth. Describe

Holometabolous, After hatching as a larva, the insect undergoes successive larval molts until a metamorphic molt causes it to enter the pupal stage. Then an imaginal molt turns it into an adult.

Representative organisms and their comparative regenerative capabilities; Hydra- Planaria- Amphibians/fish- Mammals-

Hydra- entire individual from small fragment Pl- whole anterior/posterior havles of body Amph/Fish- full limbs/ tails/ CNS/ heart/ other organs Mammals- antlers, some organs in mouse and human

Two possible mechanisms for neoblast specification during regeneration.

One proposed mechanism is that a single pluripotent neoblast is responsible for generating new cell progenitors that form the multipotent cells of the blastema. Alternatively, multipotent progenitor cells are positioned throughout the planarian with their lineages specified based on their position. These divide and produce postmitotic blastema cells that differentiate into their specified fates

Budding in hydra;

(A) A new individual buds about two-thirds of the way down the side of an adult hydra. (B) Schematic of the myoepithelium with its unipotent endodermal and ectodermal cells and its multipotent interstitial stem cells. (C) Cell movements in Hydra were traced by following the migration of labeled tissues. The arrows indicate the starting and leaving positions of the labeled cells. The bracket indicates regions in which no net cell movement took place. Cell division takes place throughout the body column except at the tentacles and foot.

Polarity in planarian regeneration

(A) Normally, Wnts are produced in the posterior blastema, and the result is a tail. If the Wnt pathway is blocked by using RNA interference against either b-catenin (B) or Wnt1 messages (C), though, the posterior blastema regenerates a head, thereby forming a worm with heads at both ends. (D) Proposed model of anterior-posterior polarity through the interactions of three signals: Erk, Notum, and Wnt. Posterior Wnt promotes tail specification while repressing head specification. Wnt inhibits the anteriorly expressed head inducer Erk. Wnt is restricted from the most anterior head regions through antagonism by Notum, however.

Regeneration of newt limbs depends on nerves

(A) Schematic of the procedure. The limb is denervated and 7 days later is amputated. After another 5 days, nAG is electroporated into the limb blastema. (B) Results show that in the denervated control (not given nAG), the amputated limb (yellow star) remains a stump. The limb that is given nAG regenerates tissues with appropriate proximal-distal polarity.

Regionally specific developmental programs; give two examples in frog By regulating the amount of T3 and TRs in their cells, the different regions of the body can respond to thyroid hormones at different times. The type of response (proliferation, apoptosis, differentiation, migration) is determined by other factors already present in the different tissues.

- A: Tail tips regress even when transplanted into the trunk. B: Eye cups remain intact even when transplanted into the regressing tail.

Certain larval structures in frogs and toads are remodeled for adults needs- give example To determine this, whole mouths were stained with alcian blue to stain cartilage and alizarin red to stain bone.

--before---> phayngeal arch cartilage is prominent, Meckle's cartilage is at the tip of the head, ceratohyal cartilage is wide and anterioraly place --- in metamorphosis--> pharygeal elongates, Meckle's elongates and mandible forms around it, ceratohyl narrows/ posteriorly located

Four major ways of regeneration; give example and draw 1) Stem-cell mediated regeneration: stem cells allow an organism to WHAT? 2) Epimorphosis: in some species, adult structures can undergo WHAT? to form a WHAT that then WHAT to form the new structure. 3) Morphallaxis: regeneration occurs through WHAT and there is little WHAT? 4) Compensation regeneration: the differentiated cells divide but maintain their differentiated functions. Such as mammalian liver.

1) regrow certain organs and tissues, planaria 2) dedifferentiation, relatively undeifferentiated mass of cells, redifferentiate, salamander 3) the repatterning of existing tissues & little new growth, hydra 4)

Modes of insect development include; _________________ (direct) development like in a silverfish. Describe

Ametabolous, After a brief pronymph stage, the insect looks like a small adult.

______________ ___________: an aggregation of relatively undifferentiated tissue.

Regeneration blastema

Amphibian metamorphosis- Growth of new structures Provide an example of this ^

Retinal projections in tadpole

________________ larvae are found among those animals whose larvae and adults possess the same basic body plan.

Secondary larvae

An example of cell death in amphibian metamorphosis is when the __________ causes the degeneration of the ________________ ________ and the ___________________ ________ that were important for larval movement and respiration but not for adult.

T3, paddle-like tail, oxygen-producing gills

Hormonal control of amphibian metamorphosis; Thyroxine (T4)- T3- T2- Tyrosine- Thyroid hormone receptors include __________ and __________

T4- relatively inactive T3 active T2 inactive Tyrosine inactive TRα TRβ

Correlation between life span and WHAT in various mammalian species.

ability of fibroblasts to repair DNA

Tadpoles are ammoniotelic, meaning they excrete ______________. Adult frogs are ureotelic, meaning they excrete ____________. Which process requires more water and what is this result of?

ammonia; urea; Tadpole one requires more water, is result of biochemical respecification in the liver

Cell-type switching in red blood cells happens in what animal and initiated by what hormone?

amphibians, T3 T3 replaces the population of larval blood cell progenitor cells with a population of adult blood cell progenitor cells

In the beginning of tail metamorphosis in amphibians resorption is an _______________ process, and in the later stage WHICH PART OF THE TAIL will be eaten by _________________? What hormone initiates this?

apoptitic, the tail muscles, macrophages, T3

polarity in planarian regen; what is the gradient? draw it

criss cross of Notum in tip and Wnt/bcat in end, rest is Erk

Metamorphosis is both a _______________ and __________________ transition. Describe the before and after in general for indirect developers

developmental and ecological transition; before baby animals have different characteristics from adult version until metamorphosis

What type of developer is a young animal that is essentially a smaller version of its adult self?

direct developer

Amphibians are named as such because amphi means ___________ and bi0s means ________. Larvae of the adult frog is called the _______________. Metamorphic changes are initiated by ___________ and ___________.

double, life; T3 and T4; tadpole

Retinal projections of metamorphosing tadpole. C: In early and middle stages of metamorphosis, axons project across the midline from one side of the brain to the other. D: In late metamorphosis, __________ is ______________ in the optic chiasm as certain ___________ are formed that project ______________.

ephrin B is produced, neurons are formed, project ipsilaterally

The emergence of urea-cycle enzyme activities correlates with what kind of metamorphic changes? ________ regulates the transcription factors to activate enzymes for the ________ _________ and to repress enzymes for the __________ _____________.

froggy re-specification types: T3 urea-cycle, ammonia synthesis

Anurans include what? Metamorphic changes in this order are triggered by what?

frogs and toads; hormonse T3 and T4 and the effector organ response

larvae stage is specialized for some function such as

growth or dispersal

Ecologically, metamorphosis is associated with changes of ____________, _____________, and ________________. Very often, larval forms are specialized for some function such as ____________ or ___________, whereas the adult is specialized for _______________.

habitat, food, behaviors; growth or dispersal, reproduction

Metamorphosis is the _________ ____________ of development

hormonal reactivation

In holometabolous insects like drosophila, most larval body gone by cell death while new adult organs develop from relatively undiffferentiated nests of __________ _________. So in larva there are 2 populations of cells: - _______________ cells; used for functions of juvinele insect - thousands of __________ cells which lie in clusters, _____________ the _______ to ______________.

imaginal cells, larval cells imaginal cells awaiting signal to differentiate

What type of developer includes a larval stage with characteristics different from the adult organism?

indirect developer

Which type of developers have metamorphosis?

indirect developers

A possible pathway for regulating longevity: ____________ signaling pathway

insulin

Flatworm regeneration and its limits (Thomas Morgan): If you bisect at the midline- If cut out a middle, top, and bottom into thirds- If small sliver-

midline= forms 2 new organisms correct 3rds= forms all 3 correct sliver= hecked up two tiny lil faces lol

Regeneration in hydra: _____________ and ____________________ 0.5 cm long; Cell movement; Continuous mitosis Dipolbastitic animals: endoderm and ectoderm _______________ stem cells found within the ectoderm layer will generate __________, ____________, __________, and ____________

morphallaxis and epimorphosis, Interstitial stem cells, neurons, secretory cells, nematocytes, and gamete

The requirement for nerves and the APC in regeneration

nAG: newt anterior gradient protein, normally supplied by the limb nerves

Thyroid hormones such as T3 (tri-iodothyronine) and T4 (thyroxide) travel through the blood to reach all the _______________ of the larvae ___________, which will respond to the hormone in one of what FOUR possible ways?

organs of the larvae anuran; growth, death, remodeling, respecificiation

Stem cell mediated regeneration organism example is what

planaria

Clonogenic neoblast: a set of _____________ ________

pluripotent cells.

Planarian regerneration is accomplished by a ____________ _______ cell population of _____________.

pluripotent stem cell population of neoblasts.

______________ larvae represents dramatically different body plans than the adult form and are morphologically distinct from the adult. NAME AN EXAMPLE

primary larvae sea urchin

Developmentally, metamorphosis involves dramatic changes which are ___________________ by specific _________________. The entire organism changes in what THREE WAYS to prepare itself for a new mode of existance?

reactivated by specific hormones; - morphologically - physiologically - behaviorally

Regeneration is the reactivation of development in postembryonic life to DO WHAT? (remember planaria)

restore missing or damaged tissues.

These pairs are examples of what kind of larvae from what kind of developer? - tadpole and frog - caterpillar and the butterfly

seconday larvae and indirect developers

Four major ways of regeneration - - - -

stem-cell mediated regeneration epimorphosis morphallaxis compensation regeneration

_______________ larva are found among those animals whose larvae and adults posses the same basic body plan, such as _________ and _________, or ____________ and ____________.

tadpole and frog, or caterpillar and the butterfly

REMODELING changes in the Xenopus skull during metamorphosis The tadpole skull is primarily _________-__________ derived ____________; the adult skull is primarily __________-_________ derived _______________.

tadpole neural-crest derived cartilage, adult neural-crest derived bone

Two distinct populations of neoblasts exist with one of them responsive to injury

the sigma neoblast population (soxP-2); and the zeta neoblast population (zfp-1) Planarian heads largely regenerate even in the absence of zeta neoblasts (leftmost, brightfield photos). Loss of the zeta population by RNAi is indicated by a lack of prog-1 expression (center photos) as seen with fluorescence in situ hybridization (FISH). Although, epidermal cell types (right) do not fully regenerate in the absence of zeta neoblasts (vim-1, purple), the remaining neoblasts (green; likely sigma) and their derived cell types are unaffected. Model of sigma neoblast-led development and regeneration. Sigma neoblasts direct the generation of numerous cell types as well as the zeta progenitor cells. Zeta neoblasts give rise to epidermal cell fates through a prog-1-positive postmitotic precursor state.

Regeneration in the larval forelimb of the spotted salamander

A: Longitudinal section of the upper arm, 2 days after amputation. The skin and muscle (M) have retracted from the tip of the humerus. B: A thin accumulation of blastema cells is seen beneath the thickened epidermis, where the apical ectodermal cap (AEC) forms at day 5. C: At day 7, a large population of mitotically active blastema cells lies distal to the humerus. D: At day 8, the blastema elongates by mitotic activity. Dedifferentiation has occurred. E: At day 9, early redifferntiation can be seen. A: apical mesenchyme; U/R: ulna and radius; P: stump; H: humerus. F: At day 10, precartilaginous condensations for the carpal bones (C) and the firs two digits can be seen.

Grafting experiments demonstrating different morphogenetic capacities in different regions of the hydra apical-basal axis;

A: Hypostome tissue grafted onto a host trunk induces a secondary axis with an extended hypostome B: Basal disc tissue grafted onto a host trunk induces a secondary axis with an extended basal disc C: If hypostome and basal disc tissues are tranplanted together, only weak or no inductions are seen.