Question

Relate methylation and homeotic control as methods of regulating gene expression in development

Answer 1

complexity of an organism is a relative term and more the complex is the ones who are ahead in evolution.

the genetic material or DNA is the source of such complexity and variability. the tight regulation of some proteins or DNA or RNA is crucial for the optimal working of some organism. there are various machinaries which can work in tandem inorder to keep this regulation possible.

Homeotic genes are the key regulatory genes that directly involved in development of particular organ, body segments or structures.almost all animals have homeotic genes which codes for transcription factor/proteins that contain a region/part called  homeodomain and are hence called Hox genes. These were first discovered in the house fly.

Methylation is a process by which methyl group is added to a DNA/protein which inturn will afect the normal functioning of the structure depending on the extend of methylation and the function of the structure. Methyaltion can be of two types.

1)DNA methylation- where a methyl group is added to the 5th position of cytosine molecule (generally)

2)histone methylation- which histone H3 lysine (generally)

methylation in mostof the time is a repressing/off switch which will turn off the the gene activity.

transcription factors(TF) enhance the transcription and help in metabolism. methylating a basepair/histone of the TF containing gene will eventually result in the non production of the required protein and will not able to perforn normal functioning. conversly some part of the genes are methylated for keeping down the gene activity.

ex: there are regions in geneome where C and G is repeted continuously called CpG island which is hyper methylated to silence the genes associated with it. loss of methylatioin will cause cancer.

homeobox genes TLX1, HOXA10 and DLX5 are some genes responsible for human placenta formation.an icrease in the methylation followed by a decrease in homeotic gene expression is associated with trophoblast differentiation, which is the outer layer of the embryo, and supplies nutrients to the embryo.

in such ways methylation and homeotic conrtol is essential for the devolopment of organism and are interrelated. Epigenetics ia an upcoming field which deals with the methylation patters and gene expression.