About

Alan L. Johnson is the Walther H. Ott Professor in Avian Biology at the Department of Animal Science at The Pennsylvania State University, a position he has held since July 1, 2009. His research focuses on understanding the patterns of ovarian function and follicle development among vertebrates, particularly in species with reproductive strategies involving limited offspring and significant maternal investment, such as mammals, birds, and some reptiles. A major area of his work involves defining the endocrine, cellular, and molecular mechanisms that govern follicle selection, a critical process in reproductive cycles that ensures the development of a specific number of ovarian follicles for ovulation. Johnson's studies utilize the domestic hen as a model system to investigate follicle selection and differentiation, exploring how inhibitory cell signaling within granulosa cell layers is alleviated to enable follicle maturation. His research examines key signaling pathways, including MAPK/Erk and PKC, and their roles in steroidogenesis and follicle atresia, which can lead to infertility if dysregulated. Additionally, he investigates the role of cell survival proteins and cell death pathways in tumor formation using human granulosa tumor cell lines. His contributions extend to understanding ovarian dynamics, follicle development, and the cellular mechanisms underlying granulosa cell differentiation and apoptosis, with implications for improving reproductive health in threatened, endangered, and domesticated avian species.

Research topics

• Biology
• Internal medicine
• Cell biology
• Endocrinology
• Andrology
• Genetics

Selected publications

• Proteome profiling of chicken ovarian follicles immediately before and after cyclic recruitment

  Molecular Reproduction and Development · 2021 · 15 citations

  Senior authorCorresponding
  • Biology
  • Cell biology
  • Internal medicine

  A shotgun proteomics study using isobaric tags for relative and absolute quantification labeling was conducted to characterize proteins in chicken ovarian follicles immediately before and after cyclic recruitment. Granulosa cell (GC) layers from the most recently recruited follicle (GC9) and from each of the four largest prerecruitment follicles (GC1-4) plus theca tissue (TH) from the most recently recruited (TH9) and largest prerecruitment (TH1) follicles were compared. Of 1535 proteins identified, none were determined to be differentially expressed between TH9 and TH1. A pairwise comparison between GC9 and GC1, GC2, GC3, or GC4 resulted in one, five, five, and six differentially expressed proteins, respectively, including yolk and cholesterol transport proteins (vitellogenin 1-3 and apolipoprotein B). In addition, transforming growth factor-beta 1 and microRNA-21 pathways were predicted to be activated at recruitment. We also report, for the first time, the expression of the neuropeptide, RELAXIN-3 (RLN3), in GC. Quantitative polymerase chain reaction determined RLN3 expression to be highest in GC9 and GC1, but its receptors, RXFP1 and RXFP3, were highest in TH and ovarian stroma, respectively. Overall, cyclic recruitment is associated with changes in protein expression predominantly within follicle GC, and a potential role for RLN3 in follicle recruitment and the initiation of GC differentiation warrants further investigation.

  PublisherDOI

• Relationship between cyclic follicle recruitment and ovulation in the hen ovary

  Poultry Science · 2019-03-06 · 13 citations

  articleOpen accessSenior authorCorresponding

  Determining whether follicle recruitment in the domestic hen is functionally linked to ovulation would inform investigations on the exact time of cyclic recruitment and subsequently, the earliest cellular event mediating recruitment. The objective of the present studies was to determine if the absence of ovulation results in the failure of cyclic recruitment. 3 groups of Hy-Line W-36 hens were studied: no-ovulation, first-ovulation, or late-ovulation within the sequence. Time and occurrence of oviposition and ovulation were documented by video recording and cloacal palpation. To determine the presence of a recently recruited follicle, ovaries were collected during the last hour of photoperiod, and follicles weighing 280 to 900 mg, with yellow yolk incorporated, and diameter of 9 to 12 mm, were considered recently recruited. To compare the amount of yolk uptake in recruited follicles, hens were fed Sudan IV dye 6 h before ovary collection. Percent dyed yolk was quantified from cross-sections of the recruited follicles. To confirm follicle viability, granulosa cell (GC) mitotic activity was assessed via flow cytometry. Initial results indicated the presence of a recently recruited follicle in 10 of 11, 7 of 10, and 9 of 10, no-ovulation, first-ovulation, and late-ovulation ovaries, respectively, with no significant differences in weight (543 ± 62 mg, 456 ± 71 mg, 620 ± 75 mg, respectively). There were no significant differences in yolk incorporation among the most recently recruited follicles with 19.0 ± 2.0%, 18.0 ± 3.7%, and 19.8 ± 3.2% dyed yolk in no-ovulation, first-ovulation, and late-ovulation ovaries, respectively. Finally, there were no significant differences in % GC in the S/G2-M phase of mitosis among recruited follicles (19.0 ± 5.0%, 22.0 ± 4.2%, 15.67 ± 1.0%, in no-ovulation, first-ovulation, and late-ovulation ovaries, respectively), confirming viability of all recruited follicles. We conclude that cyclic recruitment occurs independently of ovulation and propose that the order and timing of cyclic recruitment is predetermined at an earlier stage of follicle development.

  PublisherDOI

• Effect of varying the gate voltage scan rate in a MoS 2 /ferroelectric polymer field effect transistor

  Bulletin of the American Physical Society · 2019-03-04

  articleSenior author
  Publisher

• Regulation of vasoactive intestinal peptide receptor (VPAC) signaling in Undifferentiated hen granulosa cells

  Molecular Reproduction and Development · 2018-08-16 · 5 citations

  letterSenior authorCorresponding
  PublisherDOI

• Response of hen pre-recruitment ovarian follicles to follicle stimulating hormone, in vivo

  General and Comparative Endocrinology · 2018-10-12 · 26 citations

  articleSenior authorCorresponding
  PublisherDOI

• Follicle dynamics and granulosa cell differentiation in the turkey hen ovary

  Poultry Science · 2018-06-01 · 23 citations

  articleOpen accessSenior authorCorresponding

  Similar to the domestic hen ovary, entry of a follicle into the preovulatory hierarchy in the turkey hen represents a process in which a single follicle initiates rapid growth and final maturation prior to ovulation. Published data derived from the laying hen support the proposal that differentiation of the follicle granulosa cell (GC) layer begins coincident with entry into the rapid growth phase and is characterized by the initial capacity for follicle stimulating hormone (FSH)-mediated cell signaling. The present studies were conducted with photostimulated B.U.T. Big 6 turkey hens to compare follicle dynamics and cellular mechanisms to those in the laying hen. The measurement and weights of turkey ovarian follicles greater than 1 mm in diameter revealed a discrete size hierarchy that was maintained throughout follicle development. GC layers collected from the single follicle initiating rapid growth (at the 11 to 13 mm stage of development) and incubated, in vitro, for 3 h with recombinant human (rh) FSH (10 ng/mL) responded with significantly increased steroidogenic acute regulatory protein (STAR) mRNA expression and progesterone production. The same treatment induced minimal STAR expression and no significant progesterone accumulation in GCs from 8 to 9 mm follicles (prior to the rapid growth phase). By comparison, dispersed GCs from 8 to 9 mm follicles pre-cultured for 18 h followed by a 3 h challenge with rhFSH resulted in significantly increased STAR expression plus progesterone production. Significantly, such cultured GCs pretreated for 15 min with transforming growth factor alpha (TGFα; 10 ng/mL) completely prevented both rhFSH-induced STAR expression and progesterone production. Culture of GCs from 8 to 9 mm follicles for 21 h with Bone Morphogenetic Protein 6 (BMP6) increased both cholesterol side-chain cleavage enzyme (CYP11A1) and FSH receptor mRNA (FSHR) expression. BMP6 also enhanced rhFSH-induced STAR expression, and this effect was blocked by TGFα. Collectively, these results support a conservation of mechanisms that maintain a hierarchy of follicles throughout development plus initiate FSH-responsiveness and GC differentiation as the recruited follicle enters the rapid growth phase in these closely related species.

  PublisherDOI

• Differentiation of the granulosa layer from hen prehierarchal follicles associated with follicle‐stimulating hormone receptor signaling

  Molecular Reproduction and Development · 2018-07-11 · 32 citations

  articleOpen accessSenior authorCorresponding

  Recruitment of a single follicle into the preovulatory hierarchy of the domestic hen ovary occurs from a small cohort of prehierarchal follicles measuring 6-8 mm in diameter. We have previously reported that granulosa cells (GCs) collected from prehierarchal follicles express highest levels of membrane-localized follicle-stimulating hormone receptor (FSHR) during follicle development, yet fail to initiate signaling via cAMP following short-term incubation with FSH. Consequently, GC from prehierarchal follicles remain in an undifferentiated state and lack the capacity for steroidogenesis due to a deficiency of cAMP-dependent STAR protein and CYP11A1 gene expression. The present studies investigate FSH responsiveness in GC before and after the transition from undifferentiated to a differentiated state at follicle recruitment. Before recruitment focus is directed toward the inhibition of FSHR-signaling by β-ARRESTIN (βARR). Specifically, knockdown of βARR messenger RNA in cultured, undifferentiated GC using small interfering RNA facilitated FSH-induced cAMP formation, STAR expression, and progesterone production. Furthermore, overexpression of bovine βARR1 and G-protein-coupled receptor kinase2 in actively differentiating GC significantly decreased cAMP accumulation and progesterone production following a challenge with FSH. We propose that a βARR-mediated mechanism maintains FSHR unresponsiveness in undifferentiated GC from prehierarchal follicles, and as a result prevents GC differentiation until the time of follicle recruitment.

  PublisherOA PDFDOI

• Granulosa Cell Tumors

  2016-01-01 · 1 citations

  book-chapter
  PublisherDOI

• Anti-Müllerian hormone (AMH) receptor type II expression and AMH activity in bovine granulosa cells

  Theriogenology · 2016-05-06 · 49 citations

  articleSenior author
  PublisherDOI

• Vascular endothelial growth factor and angiopoietins during hen ovarian follicle development

  General and Comparative Endocrinology · 2016-03-17 · 37 citations

  articleSenior authorCorresponding
  PublisherDOI

Recent grants

• NIH Grant R01HD036095

  NIH · $495k · 2002

• Ovarian Follicle Selection Mediated by Release from Inhibitory Map Kinase Signaling

  NSF · $470k · 2005–2009

• Follicle Selection and Differentation in the Avian Ovary

  NSF · $261k · 2014–2018

• EFRI 2-DARE: Functionalized Monolayer Heterostructures for Biosensors with Optical Readout

  NSF · $2.2M · 2015–2020

• Cellular Determinants of Granulosa Cell Differentiation in Avian Ovarian Follicles

  NSF · $373k · 2009–2013

Frequent coauthors

• Dori C. Woods

  Universidad del Noreste

  21 shared

• J. T. Bridgham

  University of Notre Dame

  19 shared

• J. L. Tilly

  Harvard University

  18 shared

• R G Deeley

  16 shared

• Michael E. Baker

  University of California, San Diego

  16 shared

• Jerome F. Strauss

  University of Pennsylvania

  16 shared

• Noriaki Sakuragi

  16 shared

• J T Billheimer

  University of Pennsylvania

  16 shared

Labs

• Johnson LaboratoryPI

Education

• Ph.D.

  Cornell University

  1979

• M.S.

  University of Vermont

  1975

• B.A.

  University of Vermont

  1972

Awards & honors

• Zoetis Fundamental Science Award, Poultry Science Associatio…
• Recipient of the Shilts-Leonard Teaching Award for the Colle…
• Recipient of the New Jersey Agricultural Experiment Station/…