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Quiz on Wed March 14th covering only this review. Will be worth 30pts. - PowerPoint PPT Presentation


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Quiz on Wed March 14th covering only this review. Will be worth 30pts. SXL makes a functional protein in XX zygotes SXL makes a non-functional protein in XY zygotes. L is Late form made During cycle 14. E is Establisment form Made cycle 10. Where is RNA binding domain of SXL protein?.

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Presentation Transcript
slide4

SXL makes a functional protein in XX zygotes

SXL makes a non-functional protein in XY zygotes

slide5

L is Late form made

During cycle 14

E is Establisment form

Made cycle 10

Where is RNA binding domain of SXL protein?

slide6

SXL makes a functional protein in XX zygotes

SXL makes a non-functional protein in XYzygotes

Event is initiated by Exons 1+ 4

No early form of protein, thus no SXL 1/2/4 form

SXL 1/2/4 form

slide9

~Cycle 9

Cycle10-14

Zygotic transcription starts

Cycle14-and up

slide10

KEY SLIDE…Know it.

Zygotic-X chromosome factors:XSEs

2x

1x

Gro-maternal

Dpn-Zygotic

2x difference

Maternal gro

Down regulated by

Zygotic XSE proteins

Zygotic deadpan

Represses SxlPe with

Maternal gro

Development

Development

sex determination in drosophila and c elegans
Sex Determination in Drosophila and C. elegans
  • The sex determination signal in both animals is the ratio of X chromosomes to autosomes. If the ratio is 1.0 or greater, the animal is a female; if the ratio is 0.5 or less, the animal is a male.CLASSIC Definition
  • But wrong
  • In Drosophila, the key genes in sex determination encode proteins that regulate RNA processing.
sex determination in drosophila
Sex Determination in Drosophila
  • Components of the sex-determination pathway include
    • A system to ascertain the X:A ratio ,
    • A system to covert this CONCEPTUAL ratio into a developmental signal, and
    • A system to respond to this signal by producing either male or female structures.
ascertaining the x a ratio

NOT CORRECT..from book

Ascertaining the X:A Ratio
  • The system that ascertains the X:A ratio involves interactions between maternally synthesized proteins in the egg cytoplasm and embryonically synthesized proteins encoded by several X-linked genes.
  • The X-linked gene products are called numerator elements and are twice as abundant in XX embryos as in XY embryos.
  • The autosomal gene products are called denominator elements and antagonize the products of the numerator elements- NONE FOUND.
the sex lethal sxl gene
The Sex-lethal (Sxl) Gene
  • Sxl is the mater regular of the sex determination pathway in Drosophila.
  • The X:A ratio is converted into a molecular signal that controls the expression of the X-linked Sxl gene.
function of sxl
Function of SXL
  • SXL regulates splicing of its own transcript to maintain SXL protein expression in XX embryos.
  • SXL also regulates splicing of the transformer (tra) gene.
differentiating in response to the signal
Differentiating in Response to the Signal
  • TRA, along with TRA2, regulate splicing of doublesex (dsx) and fruitless (fru).
  • In XX embryos, where TRA is present, dsx transcripts are processed to encode a DSX protein that represses the genes for male development.
  • In XY embryos, where TRA is absent, dsx transcripts are processed to encode a DSX protein that represses the genes for female development.
loss of function mutations in sex determination genes in drosophila
Loss-of-Function Mutations in Sex-Determination Genes in Drosophila
  • Mutations in Sxl prevent SXL protein from being made in males; homozygous mutants would develop into males but die as embryos.
  • Mutations in transformer and transformer2 cause both XX and XY animals to develop into males.
  • Mutations in dsx cause both XX and XY embryos to develop into intersexes.
key points
Key Points
  • In Drosophila the pathway that controls sexual differentiation involves some genes that ascertain the X:A ratio, some that convert this ratio into a developmental signal, and others that respond to the signal by producing either male or female structures.
  • The Sex-lethal (Sxl) gene plays a key role in Drosophila sexual development by regulating the splicing of its own transcript and that of another gene (tra).
splicing
Splicing
  • Removal of introns must be very precise.
  • Conserved sequences for removal of the introns of nuclear mRNA genes are minimal.
    • Dinucleotide sequences at the 5’ and 3’ ends of introns.
    • An A residue about 30 nucleotides upstream from the 3’ splice site is needed for lariat formation.
types of intron excision
Types of Intron Excision
  • The introns of tRNA precursors are excised by precise endonucleolytic cleavage and ligation reactions catalyzed by special splicing endonuclease and ligase activities.
  • The introns of nuclear pre-mRNA (hnRNA) transcripts are spliced out in two-step reactions carried out by spliceosomes.
the spliceosome
The Spliceosome
  • Five snRNAs: U1, U2, U4, U5, and U6
  • Some snRNAs associate with proteins to form snRNAs (small nuclear ribonucleoproteins)
slide33

Logo for

a) Splice acceptor

b) Splice Donor

c) Initiator Met

slide34

AG/GT

CAG/NT

exon 1 intron 1 exon 2