University:
Amherst College
Course:
BIOL 220 | Developmental Biology
Academic year:

2021
Views:

279

Pages:

15
Author:

Dante Waller

What Are Gametes? • Gametes – mature form of cells set aside which will undergo meiosis and contribute a haploid chromosomal complement at fertilization to reconstitute the diploid • Egg or oocyte – large, storage • Sperm – small, motility Gametogenesis • Formation of gametes – – – – – primordial germ cell proliferation become oo- or spermato- gonia undergo meiosis become gametes • Mutations here really matter Stages of Gametogenesis • Nomenclature – gonium -> 1o -cytes -> 2o -cytes -> -tids • Progression – – – – 1 premeiotic S-phase (DNA synthesis) 2 meiotic cell divisions all 4 spermatids = in size 1 large oocyte + 2 or 3 small polar bodies When do Gametes Differentiate? • Time of differentiation – for males from haploid spermatid mature spermatozoa – for females during primary oocyte prophase I • vitellogenesis • recombination • growth How to Make a Sperm Structure of a Mammalian Testis What Cell Lineages Contribute to the Testis? • Somatic cells – Leydig – peritubular – Sertoli • Germ cells Somatic Testicular Cells SEM of Tubule Cross Section of Tubule What Are Stem Cells? • Stem cells – divide to produce 1 cell the same and one different from mother cell – thus produces unlimited supply of cells while retaining a copy in reserve of stem cell – there are also embryonic and adult stem cells of various potentials – in testis, the stem cell population is found among the spermatogonia What Controls Stem Cells? • Spermatogonial stem cells – mutations W (white-spotting) and Sl (steel) produce defects in pigment, blood and sterility – affect stem cell signaling – W = c-kit gene encoding growth factor receptor • transmembrane protein – Sl = KL encoding kit ligand • both on cell surface and secreted How Do We Know W or Sl Are Important?: Mutants in Kit How Do We Know? Experiment • KL signaling – c-kit expressed in 1o germ cells and spermatogonia – KL expressed in Sertoli and other cells interacting with germ cells – experiment: inject antibody to c-kit into peritoneum • blocks binding of KL to c-kit and inhibits proliferation Are All Testis Cells Subject to Same Signals? • Blood testis barrier – Sertoli cells make tight separation between the basal and adlumenal (near the lumen) compartments – spermatogonia are in the basal compartment but the others are in the microenvironment of the adluminal compartment controlled by the Sertoli cells

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