Development and Behavioral Gene2cs. PSC 113 Jeff Schank

Transcription

1 Development and Behavioral Gene2cs PSC 113 Jeff Schank

2 Outline Unifactorial Methods Vasopressin Deficiency Mul2 factorial Methods (Quan2ta2ve Gene2cs) Heritability The IQ Controversy What are Intelligent Tests? Are Intelligence Tests Valid? Is IQ heritable?

3 Unifactorial Methods Unifactorial gene2c analyses focus on single gene effects whereas mul2 factorial (Quan2ta2ve Gene2c) approaches focus on mul2ple gene effects Unifactorial methods typically use inbred strains of animals with a singe- gene muta2on and compare them to out bred strains Problems Not all aspects of an organism s environment are easily controlled, e.g., intrauterine, birth, and maternal effects Genes can have pleiotropic effects, which means that one gene may affect mul2ple, oven unrelated, phenotypic traits

4 A Single Gene Effect: PKU (Phenylketonuria) Is a condi2on that leads to severe intellectual impairment of human func2oning The condi2on occurs when there is a single recessive gene present in both sister chromosomes that play a role in the liver s produc2on of the enzyme phenylalanine hydroxylase Without this enzyme, the amino acid phenylalanine is not converted to tyrosine The consequence of building up phenylalanine is structural malforma2ons of the brain, resul2ng in children that are mentally retarded and irritable However, by modifying diet, to greatly lower the intake of phenylalanine, this condi2on can be largely avoided Molly's Story

5 Transgenic Organisms A knockout organism is created by disabling a specific gene A Knockin organism is created by inser2ng a specific gene into the genome Part I Part II

6 Issues with Transgenic Organisms Typically produced in inbred animals As we would predict, genes expressed earlier in development, when knocked out (in), are oven lethal Knocking out (in) a gene is somewhat analogous to making a part of a machine non- func2onal It is rela2vely easy to see how the machine breaks down, but not as easy to iden2fy the func2onal role in a complex regulatory system. This type of gene2c engineering has oven been more focused on crea2ng organisms that have some technological use such as Roundup ready plants Human insulin

7 A Natural Knockout: Vasopressin Deficiency in the Bra_leboro Rat The Bra_leboro, di/di, rat strain was discovered in the laboratory of Henry A. Schroeder in Bra_leboro, VT, USA in 1964 (Val2n Ann New York Acad Sci, 1982; 394: 1-9) It turned out to be a single base dele2on at nucleo2de 1552 in a conserved region of exon B resul2ng in a frame shiv muta2on that produces analtered amino acid sequence (Schmale, Richter Nature, 1984; 308: ) Immunohistochemical and in situ hybridiza2on studies showed that the vasopressin gene is transcribed and translated in di/di rats, but with an impaired response to physiological s2mula2on (McCabe, Morrell, Ivell, Schmale, Richter, Pfafp Neuroendocrinology, 1986; 44: )

8 Bra_leboro Rat con2nued Bra_leboro rats develop diabetes insipidus at least by the 2me of weaning with indica2ons of AVP deficiency even earlier in development (Dlouha, Nrecek, Sicha Annuls of the New York Academy of Science, 1982; 394: 10-20) AVP deficiency also affects social behavior by modula2ng aggression pair bonding social recogni2on (Caldwell, Lee, Macbeth, Young Prog Neurobiol, 2008; 84:1-24)

9 Au2sm Spectrum Disorder (ASD) What Is Au2sm Spectrum Disorder? Animal model Issues No communica2on analog Difficult to compare social deficits Difficult to compare pa_erns of behavior Possible bases for comparison General social deficits Behavior: stereotypical behavior, hyper ac2vity, sleep problems

10 ASD, Animal Models, and Vassopressin ASD may be associated with vasopressin resistance due to hyporesponsiveness of AVP V1a receptors (Boso, et al, 2007) Knockout mice lacking V1a receptors have deficits in social recogni2on resembling aspects of ASD (Bielsky, Hu, Ren, Terwilliger, Young Neuron, 2005; 47: ) Bra_leboro rats exhibit social deficits in recogni2on (Engelmann, Landgraf Physiol Behav, 1994;55:145-9) Bra_leboro rats exhibit abnormali2es in emo2onal reac2vity (Williams, Carey, Miller 1985; 6(Suppl. 1): 69-76)

11 Is AVP Deficiency Detectable in Rat Pups? FiVeen- day- old di /di pups exhibit reduced social a_achment as measured by odor preference and approach latency learning (Nelson, Panksepp. Neuroscience & Biobehavioral Reviews, 1998; 22: ) By day 10, di/di pups have an impaired adrenocor2cotropin stress response to separa2on from their mother (Zelena D et al Endocrinology, 2008) These results indicate that AVP deficiency is behaviorally detectable early in life and they are related to abnormali2es detected in adult di/di rats

12 Development in Rat Pups Figure 1. Locomotor neural development in rats has four stages. During the fetal stage, motor neurons become excitable, the CPG begins to func2on, and the first projec2ons from the brainstem develop. During the immature stage, infant rats crawl, matura2on ofposture in locomo2on proceeds cephalocaudally, the cotricospinal tract begins to develop around day 7 aver birth, and by day 10 (the end of the immature stage) coupled ac2vity in groups can be detected. During the transitory period, the eyes and ears open and walking begins. By the beginning of the adult period, adult locomo2on begins.

13 Social Behavior of Bra_leboro Rats in a Temperature Controlled Arena!

14 Measuring Behavior: Metrics Ac6vity: change in posi2on or orienta2on between each 2me interval; Distance: if ac2ve, the distance moved over a 2me interval as measured from the 2p- of- the snout Orienta6on: if ac2ve, the change in body orienta2on over a 2me interval as measured in degrees Wall contact: body contact with a wall of the arena at each 2me interval Corners: the number of corners visited by a pup during an experimental session Inner cells: the arena was divided into an array of 6 X 9 cells of equal size with inner cells defined as the number of cells not adjacent to a wall that the 2p- of- the- snout entered Outer cells: the total number of cells adjacent to a wall that the 2p- of- the- snout entered Total cells: the propor2on of the total number of cells that the 2p- of- the- snout entered. For group trials, there was one addi2onal metric Subgroups: the number of different contact groups that formed out of eight pups at each 2me interval, which ranged from 8 (no pups in contact with each other) to 1 (all pups in direct or indirect contact)

15 Were there Effects?

16 Effects of Sex?

17 7- Day Old Pups

18 10- Day Old Pups

19 Individual Metrics

20 Individual Movement Figure 3. Trajectory plots of 145 2p- of- snout points for a 12- minute session. The two plots on the lev are from two di/di, 10- day- old pups that visited four corners. The two on the right are typical one- corner visits by +/+ (top right) and +/di pups (bo_om right).

21 Group Metrics

22 Ac2vity/Inac2vity +/+ +/di di/di

23 Possible Interpreta2ons A par2cularly robust and strong result was the distance moved by 10- day old di/di pups in both individual and group trials Ten- day- old di/di pups moved over twice the distance moved by either +/+ or +/di pups in group trials For individual trials, they visited more corners, entered more cells especially those cells along walls Pups oven repeatedly circled the arena, a behavior rarely observed in either +/+ and +/di pups. Informal observa2ons of 10- day- old di/di pups revealed that they were oven able to liv their bodies off the surface of the arena and walk or run across the surface. Walking or running on the surface of the arena was never observed for either day- 10 +/+ or +/di pups Another interes2ng behavior observed in 10- day- old di/di pups was a large degree of turning

24 Conclusions Accelerated motor development also seen in ASD High degree of change in orienta2on a stereotypic behavior? Increase ac2vity with contact indicates social deficits Lower aggrega2on indicates social deficits Failure of ac2vity to decrease over 2me may be related to sleep disturbances

25 Problems There were no sex differences. Au2sm, however, occurs in males in about a 4:1 ra2o. If Vasopressin is involved in au2sm, it is far from the whole story Gene2cally, untangling the mechanisms of au2sm likely will involve understanding some rather complex gene2c networks Au2sm is not associated with diabetes insipidus, but if vasopressin is somehow involved, it may be at the receptor level and/or at the gene regulatory level How do we know we have an animal model of au2sm?

26 Mul2factorial Methods (Quan2ta2ve Gene2cs) Heritability is based on the sta2s2cal idea of variance Recall that for natural selec2on to operate in a popula2on, there must be varia2on in phenotypes If we can measure phenotypes (e.g., the height of corn plants), then we can measure varia2on using the sta2s2cal concept of variance

27 Phenotypic Variance Phenotypic variance can be par22oned into components The main empirical problem is how to es2mate each component The simplest par22on is where V G is varia2on due to gene2c factors and V E is varia2on due to environmental factors

28 Heritability Heritability in the broad sense used in the IQ controversy is: If components of variance can be es2mated for a popula2on, then h2 heritability can be used to predict characters in the next genera2on. If E(x) is the mean measure of the character for a popula2on and x MP = (x i + x j )/2 is the mid parent value, then the offspring of these parents would be expected to have a mean value of

29 Heritability Example

30 What are Intelligent Tests? The first scale for measuring intelligence was introduced by Binet in Paris for the purpose of tes2ng children in school His test was based on the concept of mental age introduce by SE Chaillé in 1887 The basic idea was to first find the average age at which most children could solve a problem, then second if say a 3 year old could solve problems solved by most 4 year olds, then his/her mental age would be 4 and his/her chronological age would be 3: Where MA is mental age and CA is chronological age

31 Tacit Assump2ons of IQ Tests Intelligence can be measured by problems that do not take too long to solve. Intelligence is black or white There are not different perspec2ves one can take to a problem Are real world problems black and white? Problem solving can be separated from knowledge This is assump2on is important for those looking for race or group differences If problem solving is not separable from knowledge, then one must show no knowledge differences between groups

32 IQ Distribu2on

33 IQ Test Items

34 Are Intelligence Tests Valid? The validity of a test refers to whether the test really measures what it is intended to measure Binet s aim was to compare the development of intelligence in children This is very different from an absolute measure of intelligence in adults IQ (and IQ equivalent tests) are only mediocre at predic2ng Job performance (at best about 50% of the variance) First year performance at university or college (about 30% of the variance)

35 Is IQ Heritable? Some people such as J. Philippe Rushton claims that there are heritable differences in IQ among groups or races of people In this video, he presents his sta2s2cal arguments If one doesn t have a basic understanding sta2s2cs and quan2ta2ve gene2cs, it is difficult to iden2fy the nonsensical use of sta2s2cs to support his agenda

36 Why Can t Heritability be Compared Between Popula2ons? Recall that the basic equa2on for par22oning phenotypic variance is The V E term for IQ tests will vary between groups if there are differences in background knowledge

37 Heritability and Corn: Two Examples Consider two completely inbred lines of corn (one tall strain and one short strain) There is no gene2c varia2on within lines because corn plants within lines are iden2cal Now if we plant them in different pots (one seed to a pot with ordinary poyng soil) and a few weeks aver they germinate, we will find varia2on in the height of the plants The varia2on will be en2rely environmental, thus V P = 0 + V E h 2 = V G /V P = 0 But, there will be gene2c differences between the two lines Trying to es2mate heritability across to popula2ons is sta2s2cally meaningless in this case

38 Second Example Now, suppose we take seeds from a sack containing seed of an open pollinated variety containing lots of gene2c varia2on We grow each group of seeds in vermiculite watered with a nutrient called Knop s solu2on, which is used by plant physiologists for controlled growth experiments Suppose however that for one group we twice as much Knop s solu2on as the other The results we get would be this: Within Knops solu2on condi2ons, V E would be very close to 0 and thus h 2 = V G /V P = 1 within groups Between groups there would be systema2c differences in height, but it would be en2rely environmental Thus, again to say that corn height is heritable across groups is sta2s2cally meaningless This is exactly analogous to the problem of different background knowledge across groups or popula2ons