P. Prabhakara Reddi, Ph.D

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P. Prabhakara Reddi, Ph.D

Reddi portrait

 

Prabhakara P. Reddi, Ph.D.

Associate Professor of Pathology


Research: 

Transcriptional Regulation of Mammalian Spermatogenesis

The long term goal of our research is to understand the mechanisms regulating mammalian spermatogenesis. The incidence of infertility is on the rise (15% in couples of reproductive age group) and the male factor accounts for approximately half the cases. Currently, treatment options for male infertility are limited due to the idiopathic nature of the disease.

The main focus of the laboratory is to understand the mechanisms involved in male germ cell-specific gene transcription. Regulation of precise spatiotemporal order of gene expression in the seminiferous epithelium is an important problem to study because disruptions thereof result in maturation arrest and male infertility. Similarly, the question of how testis-specific genes remain silent in the somatic tissues is equally important because many cancers aberrantly express spermatogenic differentiation markers (cancer-testis-antigens). We employ a combination of in vivo (mouse models) and in vitro (cell culture and biochemistry) approaches to identify critical promoter elements of testis-specific genes, their cognate transcription factors, and to study the mechanisms of regulation.  

Main findings and what they mean: We showed that insulator mediated tethering to a subnuclear structure silences testis-specific genes in the somatic tissues, and characterized a novel CpG-free and CTCF-independent vertebrate insulator located in the promoter of a spermatid-specific gene. This tethering is released in the male germ line to permit transcription. We showed that precise spatiotemporal expression within the seminiferous epithelium is coordinated in part by RNA Pol II pausing at the promoter and identified the DNA/RNA binding protein TDP-43 as a key player in the above mechanism. Our unpublished work (conditional knockout in germ and Sertoli cells) has validated that TDP-43 is essential for spermatogenesis and male fertility. The broader concepts are 1) remodeling of the nuclear lamina-chromatin interaction plays a key role in the differentiation of male germ cells, and 2) paused RNA polymerase II maintains a subset of genes in a transcription-ready state in germ cells so they can be synchronously expressed to promote differentiation. Another ongoing project in the lab is to study the role of CTCF in chromatin remodeling during the second half of spermiogenesis.

Link to Neurodegenerative Diseases

TDP-43 was a relatively unknown protein when we cloned it and reported its involvement in testis-specific gene transcription in 2006. It was discovered later the same year that TDP-43 is aberrantly expressed in a number of neurodegenerative disorders including dementia, ALS, and Alzheimer’s disease. Following this, the significance of TDP-43 has sky-rocketed and more than 1450 publications have appeared since. Still, very little is known about the function of this protein. Based on our studies in germ cells, we hypothesize that in neuronal cells TDP-43 coordinately regulates the transcription of a number of genes including those which must be in a ready-to-respond state (with paused RNA Pol II at the promoter) and that its mislocalization to the cytoplasm leads neuronal cell death due to loss of function.

 

Publications:

1: Divya Saro Varghese, Uma Chandran, Soumya A, Sathy M. Pillai, Jayakrishnan K, Reddi PP, and Pradeep G Kumar. Aberrant expression of TAR DNA binding protein-43 is associated with spermatogenic disorders in human males. Reproduction, Fertility, and Development. September 2014. “In Press”.

2: Osuru HP, Monroe JE, Chebolu AP, Akamune J, Pramoonjago P, Ranpura SA, Reddi PP. The acrosomal protein SP-10 (Acrv1) is an ideal marker for staging of the cycle of seminiferous epithelium in the mouse. Mol Reprod Dev. 2014 Aug 26. doi: 10.1002/mrd.22358. [Epub ahead of print]

3: Lalmansingh AS, Urekar CJ, Reddi PP. TDP-43 is a transcriptional repressor: the testis-specific mouse acrv1 gene is a TDP-43 target in vivo. J Biol Chem. 2011 Apr 1;286(13):10970-82. Epub 2011 Jan 20. PubMed PMID: 21252238; PubMed Central PMCID: PMC3064152.

4: Reddi PP, Urekar CJ, Abhyankar MM, Ranpura SA. Role of an insulator in testis-specific gene transcription. Ann N Y Acad Sci. 2007 Dec;1120:95-103. Review. PubMed PMID: 18184912.

5: Ranpura SA, Deshmukh U, Reddi PP. NF45 and NF90 in murine seminiferous epithelium: potential role in SP-10 gene transcription. J Androl. 2008 Mar-Apr;29(2):186-97. Epub 2007 Oct 17. PubMed PMID: 17942973.

6: Abhyankar MM, Urekar C, Reddi PP. A novel CpG-free vertebrate insulator silences the testis-specific SP-10 gene in somatic tissues: role for TDP-43 in insulator function. J Biol Chem. 2007 Dec 14;282(50):36143-54. Epub 2007 Oct 11. PubMed PMID: 17932037.

7: Acharya KK, Govind CK, Shore AN, Stoler MH, Reddi PP. cis-requirement for the maintenance of round spermatid-specific transcription. Dev Biol. 2006 Jul 15;295(2):781-90. Epub 2006 May 3. PubMed PMID: 16730344.

8: Reddi PP, Shore AN, Shapiro JA, Anderson A, Stoler MH, Acharya KK. Spermatid-specific promoter of the SP-10 gene functions as an insulator in somatic cells. Dev Biol. 2003 Oct 1;262(1):173-82. PubMed PMID:14512027